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DIY Negative Dry Etch PCB Fabrication


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This is the documentation for the method the author uses for DIY quick turn prototype printed circuit boards, (PCBs.) The documentation to the steps required is quite granular, with complete documentation, and the rationale for each step is presented with the exact equipment and materials used, along with measurements for optimizing and certifying the process. The process is based on the industry standard process used by commercial PCB vendors. The artwork for the analysis and certification procedure, 10x10.tar.gz, is available as a tape archive.

The idea being that the process could be easily replicated and functions as a base line known workable process, complete with certification and quality control methodology. The exact equipment, materials and vendors used, (as of 2017,) are listed to avoid availability issues.

The author is not affiliated in any way with any vendor, manufacturer, or distributor of equipment, components, parts, materials, or sites mentioned in this document.


Artwork generation for the PCB, (Rationale):

  1. The gEDA Project's PCB Printed Circuit Board Editor program is used to generate the artwork for the PCB.
  2. A Brother HL-2270DW Compact Laser Printer with Wireless Networking and Duplex is used for printing the PCB's artwork. The artwork is printed to a Postscript format file from the PCB Printed Circuit Board Editor program:
    
                    File->Export layout...->ps
                    check drill-helper
                    uncheck auto-mirror
                    check ps-invert
                    check multi-file
    
                

    (The remaining default Postscript options should not be altered.)

  3. The media used for printing the PCB's artwork and exposure is Strathmore 50-Sheets Laser Translucent Vellum, 8.5 x 11 Inches (598540).
  4. The Debian Linux CUPS printing command is:
    
                    lpr -P BrGenML1 -o PageSize=Letter \
                                    -o BrMediaType=PLAIN \
                                    -o Resolution=1200dpi filename.ps
    
                

    where BrGenML1 is the printer name, (found with "lpstat -a" and the options "lpoptions -l",) and filename.ps is the Postscript format file generated by the PCB Printed Circuit Board Editor program, above.

  5. Optionally, the artwork can be sprayed with Krylon K01311 Aerosol Matte Satin Finish Spray Enamel 11 Ounce for durability, and allowed to dry for at least two hours.

Cleaning the PCB, (Rationale):

  1. The PCB should be sanded on all four edges, (both the front and back edges,) with P60 sandpaper, then sanded on all four edges with 600 grit sandpaper.
  2. Acetone, (available from home improvement stores in the paint department,) should be poured on the PCB copper and flowed around the surface by tilting the PCB, then scrubbed vigorously with a paper towel dowsed in acetone.
  3. The PCB should be scrubbed vigorously with TSP, (trisodium phosphate, available from home improvement stores in the paint department,) under running water using a Scotch-Brite Non-Scratch Scrub Sponge (MP-3), 3 Count, (blue, non-scratch, is preferred over green, heavy duty.)
  4. The cleaned PCB should be placed in a container of about one liter of COLD, Ts ~ 64F, water-the container should be large enough to accommodate both hands in the water to apply the dry film to the PCB underwater.

Applying the dry film to the PCB, (Rationale):

  1. The INSMA 30cm x 5M PCB Photosensitive Dry Film For Circuit Production Photoresist Sheets should be cut to the exact dimensions of the PCB.
  2. The inside protective film should be removed with two opposing pieces of scotch tape on one corner of the dry film, and pulled apart, removing the inside protective film.
  3. The dry film should be placed on the PCB under the COLD water in the container, and positioned on a long edge of the PCB and one corner. No air bubbles are allowed between the PCB and film, (that is why the dry film is applied underwater.)
  4. The PCB and dry film should be gently removed from the COLD water in the container, and placed on a paper towel, (copper side/dry film side up,) and a flat paper towel dragged, (via the corners of the towel,) across the surface of the copper/dry film side of the PCB to remove water, (apply no pressure to the dry film.)

Laminating the dry film to the PCB, (Rationale):

  1. The PCB/dry film should be run through the AmazonBasics Thermal Laminator, using the 5 mil setting, twice with the copper side up, the short end of the PCB in first, first one short end, then the other short end.

Assembling the print frame for the PCB, (Rationale):

  1. Cut the artwork to the same size as the PCB.
  2. The artwork and PCB should be held between two 8.5" X 10" 1/8" glass plates, (available from home improvement stores,) with 1/16" neoprene, 4 Inch X 4 Inch Square Sponge Neoprene Sample Adhesive/Plain - 1/4 IN, 1/8 IN, 1/16 IN. Thick, foam under the PCB, (the same size as the PCB,) and four PCB shims, (including dry film, each with a 1/16" neoprene foam shim,) and four Acco Brands Binder Clips, Medium, 12 per Box, 2 Boxes (A7072050) for a printing frame.
  3. Turn the print frame over and the center of the PCB area pressed down and each binder clip slightly released, in turn, to compress the back glass plate, neoprene foam, PCB, and artwork against the top glass plate-this is to remove any air gap creating an off-contact exposure by forcing the glass plates in the binder clips to a flat "neutral position while compressing the artwork on the dry film and PCB. (This is particularly important with vellum media that has been wrinkled by the fusing temperature of a laser printer.)

Exposing the PCB, (Rationale):

  1. The print frame, artwork, and PCB should be exposed for 49 seconds on the SMD 5050 UV LED strip exposure stand of 150 LEDs, 1.0 inch between LEDs and PCB's dry film.

Developing the PCB, (Rationale, Alternatives):

  1. Remove the outside protective film from the dry film on the PCB, exposing the PCB for developing.
  2. The developing solution is made from 1.5 cups luke warm water (~98F, baby bottle temperature test,) with 2 heaping 1/4 teaspoon scoops of sodium carbonate, 99% Pure SODA ASH (Sodium Carbonate Anhydrous, Washing Soda) (2 lb), dissolved.
  3. The PCB scrubbed, vigorously, in the developer solution for 1 minute, with significant finger force on a microfiber cloth.

The spent developer solution will be saved for stripping the photoresist from the PCB, below.

Rinsing the PCB, (Rationale):

The PCB should be removed from the developer solution and rinsed in a container of luke warm tap water, (~98F, baby bottle temperature test,) by scrubbing the PCB, vigorously, with a microfiber cloth using significant finger pressure, for 24 to 30 seconds, (2 minutes 30 seconds to 4 minutes if the alternative developer process of floating the PCB in the developer solution is used.)

Etching the PCB, (Rationale):

The PCB should be placed in a 1 liter polypropylene, TashiBox Plastic Food Container / Food Storage / Soup Container with Lids, 32 Ounce - Set of 24 with a 2:1 H202 3%:HCL 31% new etching solution, for about 5 minutes, The 1 liter etch solution in the polypropylene container is placed in a 6 qt. plastic tray of very hot tap water, (~ 150F,) for about 15 minutes prior to etching the PCB to raise the temperature of the etch solution. The 3% H2O2 is available at the local drugstore, (usually used as an antiseptic and/or mouthwash-be careful NOT TO USE 30% H2O2,) and the 31% HCL is available at the local home improvement store in the swimming pool chemicals department.

Drilling the PCB, (Rationale):

As mentioned, above, the pads and vias for manually assembled PCBs should be as large as possible, (limited by the PDIP package,) with a minimum drill size of 0.9mm = 35 mils, and, 20 mil annular ring, (i.e., 20 mils of copper around component holes,) for a total pad diameter of 75 mils, and a clearance for the PDIP package of 20 mils between pads. For negative resist, there is a "drill helper" center punch indentation in the center of each copper pad, (and photoresist,) to assist targeting the drill bit for manually drilled component holes in the PCB.

Striping the PCB, (Rationale):

The PCB should be placed in the spent developer solution after heating the spent developer to 125F in a microwave, (for about 1 minute-it contains about as much fluid as a cup of coffee.) Stripping the photoresist takes about 5 minutes.

Soldering the PCB, (Rationale):

The soldering iron temperature for assembling components on the PCB should be set to about 350C = 662F, (but could be as low as 315C = 600F, to as high as 388C = 750F, depending on user preference,) for through hole PCB components.

Finishing the PCB:

After assembly/soldering, the flux can be removed with 91% isopropyl alcohol, (available from any pharmacy,) and an acid brush. If durability of the PCB is required, (i.e., function for years or decades,) coating the copper side of the PCB with clear acrylic spray, or fast drying polyurethane spray, (both available from home improvement stores in the paint department,) will avoid tarnishing and oxidation of the copper surface.


Cost analysis for the PCB process:

The complete bill of materials to duplicate the above process, from scratch is US $198.14, (as of 2017, and much of that cost is not necessary unless one wants to do additional process development; to only make PCBs, this cost can be reduced by approximately 75%,) which includes enough expendables for 50 ea. 100mm X 70 mm FR1 PCBs.

The incremental cost per PCB after the bill of materials is about US $0.54 in expendables, including the FR1 PCB. (The variance in cost is the H2O2 3% followed by the cost of HCL 31%.)

The fast process, (scrubbing in the developer and rinse,) takes about 12 minutes and 19 seconds process time, (plus the time it takes to clean the PCB, apply the dry film, assemble the print frame, and run the PCB through the laminator, which depends on how fast one works-typically, an additional 3 minutes-but has been done in under 1 minute on a bet.) Call it about 15 minutes to stripped PCB ready to drill and solder.


Quality Assurance/Certification for the PCB Process:

The process parameters for exposure and development of a PCB have been determined. The parameters interact, (i.e., like under exposure, and over development will sometimes work.) To determine that both processes are optimum, and optimum together, test artwork must be generated.


matrix.png

Figure I. Test Artwork Matrix

Figure I is a plot of the test artwork for the matrix PCB. The archive for the circuit, 10x10.tar.gz, is available.

The idea is that a piece of Rubylith will be placed over the artwork in the print frame, and slid down a half of a centimeter every ten seconds during exposure to vary the exposure from 0 to 200 seconds with 5 inches between the 150 X SMD 5050 UV LEDs and the PCB. The Rubylith is slid down from the top short edge, to the bottom short edge.

Then, the exposed PCB is developed, by turning the PCB vertically in the developer container, (long edge down,) and adding a half of a centimeter of developer solution every minute, for a developer time of 0 to 10 minutes.

The PCB will look like a matrix, (like a spread sheet,) of exposure time vs. developer time, and we look for the longest, narrowest, metal run and clearance as a parameter. The artwork has a 6 mil metal width, and 6 mil clearance, as the narrowest line dimension.


matrix.jpg

Figure II.

Figure II is photograph of the matrix PCB.

As oriented, the left side of the PCB is under exposed. The right side of the PCB is over exposed. The bottom of the PCB is over developed. The top of the PCB is under developed.

The best lithography, with 5 inches between the 150 X SMD 5050 UV LEDs and the PCB, occurs at an exposure time of about 4 minutes and a developer time of about 4 minutes-the 6 mil metal width and clearance is about 2 cm long in the photograph. This is in reasonable agreement with the original exposure time at 8.5" of 11 minutes, (the actual measurement made in the "Exposing the PCB, (Rationale)" Section was 9 to 13 minutes, probably closer to 9.)

The developer time of 4 minutes is in reasonable agreement with the original developer time of 5 to 8 minutes, (the actual measurment made in the "Developing the PCB, (Rationale)" Section.

And, finally, a test PCB.


10x10.png

Figure III. "10x10.png"

Figure III is a plot of the test PCB, with 10 mil line width, and 10 mil spacing. It is a rectangular spiral of 2 lines, (think of an extension cord, coiled up.) Bridging and opens can be tested with an Ohm meter, (i.e., pins 1-1 should be a short, as should pins 2-2, but pins 1-2 and 2-1 should be open.) The circuit is about 10cm X 7cm, and the total run length is about 40 feet, (20 feet for each of the two lines.) The archive for the circuit, 10x10.tar.gz, is available.


10x10.pcb.jpg

Figure IV. 10x10 PCB

Figure IV is a photograph of the test PCB, with 10 mil line width, and 10 mil spacing. It is a rectangular spiral of 2 lines, (think of an extension cord, coiled up.) Bridging and opens can be tested with an Ohm meter, (i.e., pins 1-1 should be a short, as should pins 2-2, but pins 1-2 and 2-1 should be open.) The circuit is about 10cm X 7cm, and the total run length is about 40 feet, (20 feet for each of the two lines.) The smudging is due to handling during testing, photographing, etc. The archive for the circuit, 10x10.tar.gz, is available.

A continuity test was done on the 4 pins of 10x10:

  • 1-1 short
  • 2-2 short
  • 1-2 open
  • 2-1 open

A series of 6 micro-photographs to evaluate the PCB process, made with a 100X Optical Zoom Microscope XFox Mobile Phone Microscope with Bright LED Lamp and Universal Clamp for iPhone6/6plus/5c/5s/4/4s Samsung Galaxy S6/S5/S4/Note 4/3/2 etc., and a cell phone are below. The order is the artwork, (3 photographs, left long vertical runs, top short horizontal runs, followed by a corner, with the PCB nomenclature at the bottom,) followed by the PCB photographs in approximately the same area, and the same order.


10x10.artwork.verticle.jpg

Figure V. 10x10 PCB Artwork, Verticle Runs

Figure V is a photograph of the test PCB artwork, verticle runs. The drawn metal width is 10 mils, and the clearance is 10 mils. The produced metal width is 9.4 mils, the clearance is 10.6 mils.


10x10.artwork.horizontal.jpg

Figure VI. 10x10 PCB Artwork, Horizontal Runs

Figure VI is a photograph of the test PCB Artwork, horizontal runs. The drawn metal width is 10 mils, and the clearance is 10 mils. The produced metal width is 10 mils, the clearance is 10 mils.


10x10.artwork.corner.jpg

Figure VII. 10x10 PCB Artwork, Corner Runs

Figure VII is a photograph of the test PCB artwork, corner runs.


10x10.pcb.verticle.jpg

Figure VIII. 10x10 PCB, Verticle Runs

Figure VIII is a photograph of the test PCB, verticle runs. The drawn metal width is 10 mils, and the clearance is 10 mils. The produced metal width is 8.5 mils, the clearance is 11.5 mils.


10x10.pcb.horizontal.jpg

Figure IX. 10x10 PCB, Horizontal Runs

Figure IX is a photograph of the test PCB, horizontal runs. The drawn metal width is 10 mils, and the clearance is 10 mils. The produced metal width is 8.5 mils, the clearance is 11.5 mils.


10x10.pcb.corner.jpg

Figure X. 10x10 PCB, Corner Runs

Figure X is a photograph of the test PCB, corner runs


Artwork generation for the PCB, Rationale:

3M has issued a Product Discontinuation for their transparency business. An investigation into alternative media yielded:

The minimum DIY line lithography should support Quad Flat Package geometries, meaning a minimum 10 mil line width with 10 mil clearance.

For DIY manual/hand drilled through holes, the minimum drill size is about 35 mils. If it is assumed that the minimum copper width, minimum copper clearance, and minimum annular ring are all equal, (to accomodate both positive and negative photo resist,) the critical design parameter is for the Dual in-line package with leads on 100 mil centers:

  • 100 - (2 * 17.5) = 100 - 35 = 65 mils.
  • 65 / 3 = 21 2/3 mils.

Yielding the design rules:

  • Miniumum drill = 35 mils.
  • Annular ring routing = 21 mils, DRC = 20 mils.
  • Minimum metal width routing = 21 mils, DRC = 20 mils.
  • Minimum copper width = 21 mils, DRC = 20 mils.

For DIY manual/hand drilled through holes, the gEDA Project's PCB Printed Circuit Board Editor program settings:

  • DRC, (File->Preferences->Sizes):
    • Minimum copper spacing = 19 mils
    • Minimum copper width = 19 mils
    • Minimum annular ring = 19 mils
  • Routing rules:
    • Line width = (Minimum copper width) + 1 = 19 + 1 = 20 mils
    • Clearance = (Minimum copper spacing) + 1 = 19 + 1 = 20 mils
    • Via hole size = 35 mils
    • Via ring size = (Via hole size) + (Minimum copper width) + 2 = 35 + 19 + 2 = 56 mils
    • Annular ring = 19 + 1 = 20 mils

Where 1 mil is added to the DRC dimensions to accomodate numerical issues.

For single sided quick turn prototype DIY PCBs, routing algorithms limit PCB size to about 100 mm X 70 mm, and, Uxcell a15071000ux0213 50 Piece 70 x 100 x 1.5 mm FR-4 Single Side Copper Clad PCB Laminate Board will suffice as a low cost FR1 alternative.

IPC-2221, (formerly IPC-D-275,) indicates that for 20 mil external metal widths on 1 oz/ft^2 PCB single sided material, the maximum current is 1.5A for a 10C temperature rise, and 2A under fault conditions for a 20C temperature rise. A 10C rise is safe for almost any application, and 20C is acceptable, as worst case design parameters. Note that these values are consistent with the thermal shutdown and current foldback characteristics of the LM78XX/LM79XX voltage regulators.

For commercially fabricated PCBs, 11 mil line width with 13 mil clearance, (and a drill diameter of 28 mils, annular ring of 16 mils, via hole size of 28 mils, via ring size of 62 mils,) minimum, is a reasonable commercial PCB agnostic vendor specification, (although 5 mil lithography is available, at a price.)

Note that the gEDA Project's PCB Printed Circuit Board Editor program footprint libraries are text files, and DIY PCBs and commercially fabricated PCBs have different pin geometries, suggesting shell script generated libraries:

For DIY PCB footprint library pins:

  • mask un-overlap = 3 mils
  • drillholedia = 35 mils
  • thickness = drillholedia + (2 * (Annular ring)) = 75 mils
  • clearance = 2 * (Clearance) = 40 mils
  • mask = thickness + (2 * (mask un-overlap)) = 81 mils

For commercially fabricated footprint library pins:

  • mask un-overlap = 3 mils
  • drillholedia = 28 mils
  • thickness = drillholedia + (2 * (Annular ring)) = 64 mils
  • clearance = 2 * (Clearance) = 40 mils
  • mask = thickness + (2 * (mask un-overlap)) = 70 mils

PCB Cleaning, Rationale:

The reason for sanding the edges of the PCB is the "edge lip" created by shearing the PCB to size by the manufacturer-it creates an air gap between the top glass plate of the printing frame and the PCB, resulting in the artwork not being held firmly against the PCB, creating an off-contact exposure. An off-contact exposure of 5 mil will obliterate a 10 mil clearance space between copper runs with negative resist.

The reason for cleaning the PCB with acetone is that the PCBs are shipped with an anti-tarnish film applied over the copper. The dry resist will not adhere to this film, and it must be removed.

The reason for scrubbing the PCB with (trisodium phosphate,) is to clean oils off of the copper, (from finger prints in handling, etc.) Note that surfactant based cleaners, (such as dish washing liquid,) can not be used since they leave a surfactant film on the copper. The dry resist will not adhere to the surfactant film.


Applying the dry film to the PCB, Rationale:

The objective is not to remove the water between the PCB and dry film, which will act as a lubricant in the lamination process-the PCB and dry film should not be in contact, but separated by a thin sheet of water. The remaining water should be removed, via the paper towels, to keep water out of the laminator. Wet lamination is recommended in Dupont Riston General Processing Guide, (assumed to be representative of the dry film product INSMA 30cm x 5M PCB Photosensitive Dry Film For Circuit Production Photoresist Sheets used in this project)


Laminating the dry film to the PCB, Rationale:

From Dupont Riston General Processing Guide, (assumed to be representative of the dry film product INSMA 30cm x 5M PCB Photosensitive Dry Film For Circuit Production Photoresist Sheets used in this project):

  1. Roller pressure: 43 PSI to 72 PSI ~ 57.5 PSI
  2. Roller temperature: 100C to 125C ~ 112.5 C = 234.5F
  3. Roll speed: 2-5 feet per minute
  4. Exit temperature: 150F inner layer, 120F outer layer

By comparison with the AmazonBasics Thermal Laminator, using the 5 mil setting:

  1. The exit temperatures, (5 mil laminator setting,) of the PCB from the AmazonBasics laminator were 124F on the first pass, and 142F on the second and final pass, measured with a Temp Meter Temperature Gun Non-contact Digital Laser Infrared IR Thermometer New infrared thermometer.
  2. The AmazonBasics laminator has a roller temperature of about 225F, (for the heated aluminium shroud on the lower roller,) and a speed of 4 inches in 20 seconds, or about a foot a minute, or two passes would be required, with an exit temperature on the second pass of about 142F, (all measured with the infrared thermometer.)

Note that folding the PCB in a piece of copier paper and pressing down on the PCB/dry film surface with a clothes iron set to about 110C for several minutes will suffice for laminating the dry film to the PCB.


Assembling the print frame for the PCB, Rationale:

Off-contact printing is the nemisis of DIY PCB fabrication.

Consider an exposure of a PCB to a 5" X 5" array of UV LEDs, mounted 5" above the PCB, and positive photo resist artwork.

Now, consider what happens to the area on the PCB directly under the one of the LEDs on the extreme left of the UV LED array. It receives UV light from the LED directly above the PCB.

Additionally it receives UV light from, say, a UV LED on the extreme right of the LED array. Note that this light is slanted at a 45 degree angle, (e.g., 5" away, and 5" height, in this example.)

Now, suppose the artwork on the PCB is raised 5 mils, (about twice the diameter of a human hair.) From basic trigonometry, the light from the far right UV LED has encroached under the artwork by 5 mils. A 10 mil copper width run is now 5 mils wide.

If we have encroachment from the other side, (due, perhaps, to overlap of the UV LED array,) we loose another 5 mils in copper width on the other side of the copper run, and the copper run is obliterated.

For negative photo resist, it is the 10 mil space between copper runs that is obliterated.


There are several issues that can raise the artwork off of the PCB, creating off-contact exposure:

  1. The fusing heat of a laser printer can wrinkle the artwork's media, (particularly with vellum media.)
  2. The PCB itself is not flat, but slightly curved.
  3. The PCB "edge lip" created by shearing the PCB to size by the manufacturer.

Note that pressing down on the PCB/dry etch assembly from the edges of top glass plate, (as in a traditional print frame,) yields a curvature in the middle of the top plate, (and off-contact printing,) due to the thickness of the PCB, of the form, (in one dimension):



            K * (3 * l^3 + 4 a^2)

        

K a constant, l the length of the PCB, a the overlap of the PCB by the top glass.

The solution, (at least a partial solution,) is to shim the print frame edges under the clamps to the same thickness as the PCB in the middle of the print frame. The shims are made from PCB, of the same thickness, including dry film, and use very thin foam under the shims, and, PCB.


printframe1.jpg

Figure XI. Print Frame Assembly Parts

Figure XI is photograph of the print frame before assembly.


printframe2.jpg

Figure XII. Print Frame Assembly

Figure XII is photograph of the assembled print frame. The PCB is under the artwork. The thickness of shims under the clamps is (nearly,) identical to the thickness under the artwork. Both the top glass plate and bottom glass plate are in a (near,) neutral position and stress.


Exposing the PCB, Rationale:

There are two programs that will be helpful in designing the PCB UV exposure:

  1. isotropic.array.gp, which is a Gnuplot, (using GNU Emacs script,) which plots the UV light intensity of a linear array of UV LEDs, (the UV LEDs are assumed to be an isotropic light source.) The objective is to find the minimum height above the PCB artwork such that the UV light intensity across the PCB is a smooth curve, preferably as flat as possible, (as opposed to having waves under each LED in the linear array.)
  2. isotropic.array.py, which is a Python script, that makes a Gnuplot compatible data file of the UV light intensity of a two dimensional array of UV LEDs, (The UV LEDs are assumed to be an isotropic light source.) The objective is to display the UV light intensity on the PCB under each UV LED, varying the LED array's parameters, such as height above the artwork, distance between LEDs, etc.

leds.jpg

Figure XIII. UV LED Array

Figure XIII is photograph of the 10 X 15 UV LED array. The array was constructed out of SMD 5050 UV strip LEDs, DC12V 3528/5050 UV Ultraviolet purple waterproof 60led/m Strip lamp black light, and uses the power supply, AC TO DC 12V 5A 60W Regulated Switching Power Supply Adapter for LED Strip Light. These were mounted on 2 Pcs Prototyping Universal Copper Rectangle PCB Print Circuit Board 18cm x 30cm. The UV LED strips are 1/60 of a meter apart, (the same as the UV LED spacing along each strip,) to facilitate hookup of the UV LED strips to terminal blocks which connect to the power supply. The frame was constructed out of scrap lumber. The UV LED array has legs, (of varying length, for experimental purposes,) that are easily detached, (like an in-bed breakfast table.)

A setup was made under the SMD 5050 UV LED strip exposure stand of 150 LEDs, 8.25 inches between LEDs and dry film, Ta = 59.3F, (e.g., garage temperature,) from the top, down:

  1. Top, glass plate
  2. Sliding RUBYLITH - SINGLE SHEET - SIZE 11" X 14" RED, at 1/2" intervals
  3. A blank sheet of Strathmore 50-Sheets Laser Translucent Vellum, 8.5 x 11 Inches (598540).
  4. A strip of dry etch film
  5. Bottom, white copier sheet of paper with 1/2" marks

Such that the Rubylith can be slid down, exposing the dry film, more at the top, less at the bottom.

The Rubylith was slid down, 1/2" per minute for 20 minutes, to expose the dry etch film at calibrated exposure levels.

By eye, there was no change in the blue color after 9 minutes of exposure.

Shining a white LED light through the exposed dry film and measuring the light intensity with a LUX meter indicated no difference in the blue color after 11 to 13 minutes of exposure. (Note that this is not a precise measurement-the white LED further exposes the dry film, and the LUX meter sensitivity to UV is down by about 90%.)

The SMD 5050 10 X 15 UV LED array exposure time is now calibrated for an 8.5" distance between the LED array and the INSMA 30cm x 5M PCB Photosensitive Dry Film For Circuit Production Photoresist Sheets, at about 9 to 11 minutes.

In an effort to reduce the effects of off-contact exposure, the light from the LEDs was narrowed for each LED by reducing the distance between the LEDs and artwork/PCB from 8.5" to 1.0" This reduces the field of light projected on the artwork/PCB for each LED. Using the isotropic.array.py program, and the fact that light intensity decreases with the square of the distance from the source:

  1. I8.5 = 130 in the center of the LED array for 8.5" separation between the LEDs and artwork/PCB.
  2. I1.0" = 22 in the center of the LED array for 1" separation between the LEDs and artwork/PCB.

Meaning:

  1. The exposure would have to be increased by a factor of 130 / 22 = 5.9.
  2. The light intensity would be increased by a factor of (8.5 / 1.0)^2 = 72.3, i.e., the exposure would have to be reduced by a factor of 72.3.

For a total exposure time at 1" separation between the UV LEDs and the dry film of (5.9 / 72.3) * 10 minutes = 0.186 minutes = 49 seconds.

It may seem counter intuitive to reduce the distance between the UV LEDs and dry film to reduce the effects of off-contact printing.

The effect can be demonstrated with an LED flashlight suspended over a table, (by arm.)

Observe the diameter of the lighted spot on the table at, say, a distance of 20 inches. Approximate the outer edge of the lighted spot with a marker of some sort, (a small piece of paper will do.)

Now, lower the flashlight vertically, (over the same spot on the table,) to a distance of a few inches, and notice the lighted spot is much brighter, but much smaller in diameter. Further, notice there is almost no light at the marker made at 20 inch distance between the UV LEDs and table.

The reason is that the cumulative light intensity, (at any point on the PCB,) increases at a faster rate, than the decrease in light from adjacent LEDs in the array as the distance between the UV LEDs and dry etch film is decreased.

Which means the exposure time can be reduced, reducing the cumulative exposure to UV light in areas created by off-contact printing.


The emperical data was taken at Ta = 59.3F. To calculate the exposure times for different temperatures, from the Arrhenius Equation:



            k = exp (-0.0385 * (T1 - T0))

        

where T0 is the temperature, (above,) and T1 is a different temperature, (probably the different ambient temperature,) both in degrees C, and k is the factor that the above times will reduced by, (assuming T1 > T0.)

Addendum: Lestraveled mentions in Project: Photographic methods of making PCBs that a point source UV source is a solution to off-contact printing problem, (by, essentially, collimating the UV light.)

His arguments have merit, and 3W 5W 10W 20W 30W 50W 100W High Power UV Ultrat Violet LED Beads Lamp Light Chip may be a viable alternative, (the 5W with PCB, 360-365 nm version is probably the best choice for a UV light source, in series with a 10 Ohm at least 20W resistor, Cutequeen 2PCS 25W Watt 10 Ohm Aluminum Case Wirewound Chassis Mounted Resistor (pack of 2), and a 12V with at least 2A power supply, for example, AC TO DC 12V 5A 60W Regulated Switching Power Supply Adapter for LED Strip Light, which would have other uses.)



Developing the PCB, Rationale:

One heaping 1/4 teaspoon of sodium carbonate, 99% Pure SODA ASH (Sodium Carbonate Anhydrous, Washing Soda) (2 lb), is 2 gr.

A 50% exposed, double sided, PCB will consume about 1 gallon of dry film developer, 99% Pure SODA ASH (Sodium Carbonate Anhydrous, Washing Soda) (2 lb), per square foot of PCB, meaning a 10cm X 7cm board will consume 0.0753 gallon of developer solution, and 1 cup of developer solution is 0.0625 gallon, or 0.0753 / 0.0625 = 1.2048 cup is required, for an equivalent industry standard process, Printed Circuit Board Fabrication - Developing, meaning about 1.5 cups of developer will be required.

From Dupont Riston General Processing Guide, (assumed to be representative of the dry film product INSMA 30cm x 5M PCB Photosensitive Dry Film For Circuit Production Photoresist Sheets used in this project,) the weight of the sodium carbonate should be about 1% of the weight of the water it is dissolved in, i.e., 10 gr. of sodium carbonate per liter of water. 1 Cup = 240 Milliliter, or the 1.5 cups of water weighs 240 gr. * 1.5 = 360 gr. The sodium carbonate should weigh 1% of 360 gr., or 3.6 gr. This means that two heaping 1/4 teaspoon of sodium carbonate per 1.5 cups of water would be recommended.

From Dupont Riston General Processing Guide, (assumed to be representative of the dry film product INSMA 30cm x 5M PCB Photosensitive Dry Film For Circuit Production Photoresist Sheets used in this project):

"The easiest method for determining the breakpoint is: Mark several copper panels with non-permanent water soluble felt tipped (such as Staedler Lumocolor 355 Non-permanent or Vis-a-Vis Overhead pen.) Laminate the panels with resist. Remove the polyester coversheet and develop the panel. When the panel is at about 65% of the developing chamber length, stop the sprays and conveyor. The marking ink will be washed off the panel surface as soon as the resist has been developed, thus indicating the breakpoint."

Note that the time the PCB is in the developer solution in production will be 1.6 to 2.0 times this breakpoint.

Three PCBs were scrubbed, (acetone and TSP,) marked with many Expo Vis-A-Vis Wet-Erase Overhead Transparency Markers, Fine Point, Black, lines, and laminated with dry film, twice through the AmazonBasics laminator set on 5 mil, and each developed in a solution made from luke warm water, Ts = ~98F, two heaping 1/4 tsp of 99% Pure SODA ASH (Sodium Carbonate Anhydrous, Washing Soda) (2 lb) per 1.5 cups of water:

  1. The first PCB placed in the developer solution, copper side down in the solution, with a small "tented" handle of cellophane tape attached to the back of the PCB for inspection of the developing process-white "tentacles" will flow down from the copper surface of the PCB:
    1. The Expo Vis-A-Vis Wet-Erase Overhead Transparency Markers, Fine Point, Black, lines started to disappear in 3 minutes and were obliterated in 4 minutes.
    2. For the first methodology, the developer time would be between 1.6 * 3 = 4.8 minutes and 2 * 4 = 8 minutes.
  2. The second PCB was placed in the bottom of the developer solution, copper side up, and scrubbed, vigorously with pressure, with a microfiber cloth:
    1. The Expo Vis-A-Vis Wet-Erase Overhead Transparency Markers, Fine Point, Black, lines were obliterated in 30 seconds.
    2. For the second methodology, the developer time would be between 1.6 * 30 = 48 seconds and 2 * 30 = 60 seconds.
  3. The third PCB was placed in the bottom of the developer solution, copper side up, and the solution rocked back and forth:
    1. The Expo Vis-A-Vis Wet-Erase Overhead Transparency Markers, Fine Point, Black, lines started to disappear in 2 minutes and were obliterated in 3 minutes.
    2. For the third methodology, the developer time would be between 1.6 * 2 = 3.2 minutes = 3 minutes 12 seconds and 2 * 3 = 6 minutes.

Note that there are three methods of developing the PCB. The third is conventional, and has been used successfully by DIY'ers for over 50 years. Only two methods will be pursued in this project, the first and the second methods:

  • The PCB placed in the developer solution, copper side down in the solution, with a small "tented" handle of cellophane tape attached to the back of the PCB for inspection of the developing process-white "tentacles" will flow down from the copper surface of the PCB. This is the easiest and cleanest method. The development time is 5 to 8 minutes.
  • The PCB placed in the bottom of the developer solution, copper side up, and scrubbed, vigorously with pressure, with a microfiber cloth. This is the fastest method, but is messy, and should occur under, at least subdued light, or safe light. This method is, also, prone to unequal developing over the entire PCB surface, depending on how ubiquitous the force of manual intervention. The development time is 48 to 60 seconds.

The emperical data for development time methodologies was taken at Ts = 98F. To calculate the exposure times for different temperatures, from the Arrhenius Equation:



            k = exp (-0.0385 * (T1 - T0))

        

where T0 is the temperature, (above,) and T1 is a different temperature, both in degrees C, and k is the factor that the above times will reduced by, (assuming T1 > T0.)

Note that there were safety considerations in the design of the development process. Specifically, sodium carbonate is similar to household baking soda. In point of fact, if food grade household baking soda is heated to about 350F in an oven, gas will escape from the baking soda, leaving a white powder-sodium carbonate. Actually, in a pinch, household baking soda can be used instead of sodium carbonate.


Rinsing the PCB, Rationale:

The rinsing is important, and should be half the developer time, as per Dupont Riston General Processing Guide, (assumed to be representative of the dry film product INSMA 30cm x 5M PCB Photosensitive Dry Film For Circuit Production Photoresist Sheets used in this project.)


Etching the PCB, Rationale:

From Etching with Air Regenerated Acid Cupric Chloride:

"For typical double sided PCB with 36um thick foil thickness and 50% pattern coverage, then a safe estimate of minimum volume of enchant per unit board area calculates out to be 1.6 liters/dm2 (16 ml/cm2)."

Each 10cm X 7cm PCB is 70 cm^2, or 1.12L if the PCB was double sided, or the one liter polypropylene container, (TashiBox Plastic Food Container / Food Storage / Soup Container with Lids, 32 Ounce - Set of 24,) would contain enough etching solution for two single sided PCBs before regeneration was required.

The emperical data for the etching time methodology was taken at Ts = 110F. To calculate the etching time for different temperatures, from the Arrhenius Equation:



            k = exp (-0.0385 * (T1 - T0))

        

where T0 is the temperature, (above,) and T1 is a different temperature, both in degrees C, and k is the factor that the above times will reduced by, (assuming T1 > T0.)

Note that there were safety considerations in the design of the etching process. Specifically, the chlorine concentration in the etching solution is about twice that of household bleach, (i.e., "Clorox.") One ALWAYS, (repeat, ALWAYS,) adds acid to water, (HCL to H2O2 in this case, which is the way the solution is made.) An inadvertent spill of the etching solution goes into tap water. It is not as convenient as electrically heated etching solution, but relatively safe. Usually, one liter of the solution is made first, (remember, ALWAYS, HCL into H2O2,) and placed in the container with hot tap water-by the time for the etching solution, it is about 100F.


Drilling the PCB, Rationale:

For occasional PCB development where precision is not necessary, an Archimedes drill, (for example, In-tool-home Semi-automatic Spiral Drill with Spring Hand Chuck Pin Vise with Twist Drill Bits Set of 21,) is a cost effective alternative for a small number of PCB holes.

Although there are commercial drill presses available in the US $50 to $100 range that work well for manually drilled PCBs with holes of 0.9mm = 35 mil, finer line widths usually require a special purpose built drill press.


drillpress.jpg

Figure XIV. Drill Press

Figure XIV is photograph of a simple, easy to construct, and relatively inexpensive drill press. For precision, it is based on 2Pcs 8mm 200mm Linear Shaft Rod Rail Kit W/ Bearing Block For 3D Printer CNC and Electric Hand Drill DIY set DC12V Motor w/Twist Drill Bits 2.3mm Chuck Bracket which is powered by a AC110V TO DC Adjustable 3-12V 1A Power Supply Adapter for Electric Drill Motor Hand Drill, (not shown,) to control the drill motor speed and 2.3mm+10Pcs 0.5-3.2mm Micro Twist Hand Drill Kit Chuck Electric Drill Bit Collet which has a 1/8" = 3.17mm collet for standard CNC bits with 1/8" shanks.

The frame of the drill press was made using a plunge router, an end mill bit, straight edge, 90 degree triangle, electric drill, and a drill guide. All MDF was cut to shape with the plunge router-but simple manual/electric saws can be used, with substantial sanding to true the sides and orthogonality of corners.

The cost of the drill press is about US $30, (but shop around at the Internet stores-the prices are very variable, sometimes daily.)


drillpress28.jpg

Figure XV. Drill Press Work Sheet

Figure XV is the drill press work sheet, (large PNG format, or in original XFig format, drillpress28.fig.gz.)

The frame is a semi-diagonal tensile field torque box design, (the back and top of the box are not shown in the drawing.) The frame is constructed from 1/2" = 12mm and 1/4" = 6mm MDF. The majority of the pieces are the same width, (and like pieces can be trued by clamping all like pieces together and sanding.) The design is ratiometric and jigging is not required-only clamping during gluing, (preferably with carpenter clamps-duct tape has been used as an alternative.) The objective was a simple structure that could be made with manual tools, (and a lot of sanding,) or, a CNC router table with manual crafted G-code.

Chladni Vibrating Plate Resonances:



            c = 1126 ft/sec, speed of sound
            a = 9.5" = 0.8 ft, longest edge
            b = 5.15" = 0.44 ft, next longest edge
            m = 1, lowest resonance due to next longest edge
            n = 1, lowest resonance due to longest edge
            f = (c / 2) * sqrt ((n / a)^2 + (m / b)^2)
            f = 1460 Hz., the resonance of the largest plate.

        

22,000 rpm is the maximum rating on the motor, or 367 Hz. = rps, a factor of 60, in frequency, below the lowest plate resonance of the drill press. A frequency factor of 60 is -36 dB damping for parasitic vibrations of the motor, (assuming a simple single pole Bode plot response,) adequate for damping motor vibration of the plate. A safety factor of two would seem appropriate, (as always in engineering, and is used throughout this document,) indicating a maximum speed of 10,000 rpm, which corresponds to 5.5V.

Note that there is no quill, (the mechanism that moves the drill up and down,) since many have their own opinions on how that should be implemented for PCB work (see Quill Return Alternatives for examples):

  • Obviously, a twin axis lever arm attached to one side of the frame and the side of adapter plate, (like a standard drill press,) is a simple solution, perhaps with a return spring attached to the lever arm.
  • A favorite is a small, low bar on the adapter plate that can be "pinky" operated, allowing the PCB to be stabilized with both hands, and the hole drilled with the "pinky."
  • For fine line, precision PCB work, the quill action can be implemented with an analog RC model airplane servo, (44 oz-in = 3.2 kg-cm stall torque,) controlled by TLC555CP timer circuit to set the feed rate of the drill press. (There is another advantage since the electric control of the quill permits up/down to be foot operated.) Linkage alternatives can be found in the Internet stores in the RC model car/airplane section.

Note that there is an alignment procedure in the drill press work sheet. Elaborating:

  1. First, assemble the adapter plate and four SCS8UUs with two fasteners, each SCS8UU, in diagonal corners, (finger tight, say, the upper right, and lower left corner.)
  2. Insert a rail shaft in one side of the adapter plate and two SCS8UUs. Extend the rail shaft and approximate extending the shaft from one SCS8UU to the center of the linear bearing of the other SCS8UU, for both SCS8UUs. Torque the two fasteners in each SCS8UU. One side of the adapter plate and its two SCS8UUs are now aligned. Verify that sliding the two SCS8UUs and adapter plate on the rail shaft is smooth.
  3. Likewise on the other side of the adapter plate and remaining two SCS8UUs, but with a caliper measure for identical distance between rail shafts at each SCS8UU, and, at the end of the rail shaft, fully extended in both directions. Torque the two fasteners in each SCS8UU. The two rail shafts are aligned, parallel. Verify that sliding the two SCS8UUs and adapter plate on the rail shaft is smooth.
  4. Insert, and torque the remaining fasteners in the SCS8UUs on the adapter plate.
  5. Assemble the four SK8s on the frame, two fasteners each, finger tight.
  6. Insert the rail shafts, on both sides, through the SK8s and SCS8UUs. Wiggle the SK8s for free alignment with the parallel rail shafts on the adapter board, and torque all 8 fasteners. Verify that sliding the adapter plate on the rail shafts is smooth. There should be very little play/runout of the adapter plate assembly.

If standard twist drills are to be accommodated, it may be necessary to increase the length of the rail shafts. The maximum chuck/collet diameter is 1/8", and the 1/8" jobber bit drill length is 2 3/4".

Additionally, the drill press can be used for cutting and trimming the edges of PCBs using 10X 1/8" Carbide Flat Nose End Mill CNC Router Bits Double Flute Spiral 17mm USA by locking down the quill, and using a fence guide, (like a table router, or scroll router.) However, the feed rate is quite slow. (The author cuts PCBs with a cheap miter box, and a hack saw with a fine tooth blade.)


0.9mm-hole.jpg

Figure XVI. Photograph of a 0.9mm Hole Made With a 0.9mm CNC Bit

Figure XVI is a photograph of a 0.9mm = 35 mil hole made with a 0.9mm CNC bit in the drill press. The hole was drilled through from the copper side. The photograph is of the copper side of the hole. The cutting speed was 19,300 RPM, (unloaded,) and the hole was not burnished.

To measure the dimensions of the drilled hole, a caliper was set to 35 mils, and photographed:


0.9mm-caliper.jpg

Figure XVII. Photograph of a Caliper Set to 35 mils

Figure XVII is a photograph of a caliper set to 35 mils. Both photographs were printed and held up to light to judge the roundness of the hole in all directions. The two photographs were twisted to measure the diameter of the hole, and found to be 0.4 mil larger than the drill that made the hole. (Note that 0.9mm = 35.433 mils, so the produced hole diameter may be more accurate than the 0.4 mil due to limitations of measurement technique-caliper setting, photographic distortion, etc.)

The lateral end play of the 0.9mm = 35 mil CNC drill bit was measured with a dial indicator and found to be +/- 1 mil in all directions.

The hole measurements of the drill press are commensurate with AND10387:

  • Hole dia: +4 mil / -1 mil
  • Manual location: 20 mil
  • CNC location: 3 mil
  • Drill bushing location: 8 mil

For fine line PCB work, note the "Manual location: 20 mil" error in the industry standard specification. To achieve "CNC location: 3 mil" capability, the model airplane servo actuated quill, and 800X 8 LED 2 Mega Pixels USB Digital Microscope Endoscope Camera Video Magnifier to optically align the drill bit over the hole location will be required. This is not necessary for pad diameters of 75 mils and minimum bit diameter of 35 mils.


0.3mm-hole.jpg

Figure XVIII. Photograph of a 0.3mm Hole Made With a 0.3mm CNC Bit

Figure XVIII is a photograph of a 0.3mm = 12 mil hole made with a 0.3mm CNC bit in the drill press. The hole was drilled through from the copper side. The photograph is of the copper side of the hole. The cutting speed was reduced to 15,100 RPM, (unloaded,) and the hole was not burnished. Unfortunately, the author has no provision for measuring the dimensional characteristics. The specific hole was from 10 X 10 array, (100 holes,) which required about 20 seconds a hole, (about 30 minutes, total-most of the time in targeting the drill bit.)

Some assistance can be provided by using magnifier glasses, (for example, Beileshi 5Lens Glass Magnifying Visor Magnifier Glasses With 2 LED Professional Jeweler's Loupe Light Bracket and Headband are Interchangeable,) and, perhaps, adding several 100Pcs 5mm White Ultra-Bright LED Light Lamp Emitting Diodes 15000MCD lot DP to the bottom of the adapter plate, aimed at the tip of the CNC drill bit, (perhaps powered by a 5V "wall wort," through a current limiting resistor.)

Quill Return Alternatives:

There are many quill return alternatives, mostly dependent on user preferences and cost constraints. A few examples are listed below, with the exact parts used for replication purposes-but resourcefulness is appropriate.


rubber-bands.jpg

Figure XIX. Photograph of Using Rubber Bands for the Quill Return

Figure XIX is a photograph of the drill press using simple rubber bands for quill return. The rubber bands will have to be replaced periodically, but for occasional use, it is an effective solution. The rubber bands are available at office supply stores, or the Internet stores. The ones shown are about 2.5" in diameter, and about 1/16" thick.


springs.jpg

Figure XX. Photograph of Using Springs for the Quill Return

Figure XX is a photograph of using springs for the quill return. The springs shown are 10 Pcs Small Compression Springs 40mm Long x 10 mm OD (Nominal), which fit quite tightly around the rail shafts. The washers are standard 8mm. The springs are strong, and a lever actuated handle will probably be required, (much like a standard drill press.) Team Associated 1/10 12MM Front Spring Black 3.00 #91326 Sealed have also been used with 10mm washers-but the springs are very strong.


hook.jpg

Figure XXI. Photograph of Using a Counter Weight for the Quill Return

Figure XXI is a photograph of using a counter weight for the quill return. The photograph is the back of the adapter plate where the actuating string for the counter weight is attached. The face plate and motor assembly weigh about one pound. The actuating string will have a tension of about one pound. At least a ten X safety factor was deemed reasonable, and KastKing DuraBlend Monofilament Leader Line, which is at least 20 pound test, was used for the actuating string. The hardware, (all at least 20 pound test,) used was SHELURE Duo-lock Lock Snaps Nice Swivel For Fishing Saltwater Solid Rings Fishing Connector, Dr.Fish Rolling Barrel Fishing Swivel Stainless Steel Black Nickel, and, American Fishing Wire Single Barrel Crimp Sleeves.

The counter weight, (of 2 to 3 cubic inches of metal-coins, fishing weights, etc.,) is suspended inside the frame, and attached to the adapter plate in the center, (via the actuating string,) through two CTYRZCH 10pcs 3D Printer Extruder U-groove Guide Wheel Size 4134mm bearings mounted on top of the frame face. This is a nice alternative since the force remains constant to move the drill motor/adapter plate up and down with minimal force. This frees the index finger and thumb of both hands to stabilize the PCB during drilling, the quill being actuated by the smaller fingers on one hand through a small handle rigidly attached to the bottom of the adapter plate.


counter-weight.jpg

Figure XXII. Photograph of Using a Counter Weight for the Quill Return

Figure XXII is a photograph of using a counter weight for the quill return. The photograph is the top of the drill press, and shows the KastKing DuraBlend Monofilament Leader Line running from the adapter plate, over the top of the drill press, and down to a counter weight of about 175 US pennies in a large pill bottle. The CTYRZCH 10pcs 3D Printer Extruder U-groove Guide Wheel Size 4134mm bearings mounted on top of the frame face are visable.


via-array.jpg

Figure XXIII. Photograph of the via-array test PCB

Figure XXIII is a photograph of a test/QA PCB consisting of 988 vias filling a 10 cm X 7 cm PCB, (38 X 26 vias.) The holes were drilled with the drill press and a 0.3 mm ~ 12 mil diameter CNC drill, averaging about 4 seconds per hole, (i.e., a little over an hour for all 988 holes-excluding breaks.) The artwork for the test PCB, via-array.tar.gz, is available as a tape archive.

There were no drill bit breakages, (only one bit was used,) and a cursory check of the hole positioning was about 3 mils, RMS, (about 4 mils maximum,) which is commensurate with AND10387:

  • Hole dia: +4 mil / -1 mil
  • Manual location: 20 mil
  • CNC location: 3 mil
  • Drill bushing location: 8 mil

Installing the collet and CNC bits:

Installing the collet is only required for a new motor or new collet.

  1. Use a dial indicator to verify the run out of the motor shaft, (at the tip of the motor shaft.)
  2. Finger tighten the two opposing set screws of the collet shaft, installing the collet shaft on the motor shaft:
    1. With a dial indicator, tighten the two opposing set screws, checking the run out of the collet shaft at the position of the set screws.
    2. With a dial indicator, check the run out of the collet shaft between the position of the set screws move the collet shaft for minimum run out. The collet shaft is now installed.
  3. Install the collet chuck and finger tighten the collet lock nut around the CNC bit such that the CNC bit will move freely, up and down in the collet, (tighten the collet lock nut as tight as possible, but the CNC bit should move up and down freely-twist the CNC bit in the collet to verify that the CNC bit moves up and down in different positions):
    1. Position the drill press over a scrap of PCB material, (copper side up,) with the CNC bit tip on the PCB copper, and the top of the CNC bit with about 1/16" clearance from the top of the collet, (there should be about 1/16" clearance between the CNC bit and as far as the CNC bit will go into the collet.) It is important that the drill press is stable in this position.
    2. Turn the drill motor power on, (the CNC bit should wobble, then straighten vertically with the tip on the PCB, and the CNC bit shaft in the collet-i.e., a self aligned concentric installation of the CNC bit.)
    3. Gently pinch the collet lock nut, with equal pressure from the thumb and forefinger, to tighten the collet lock nut. The finger pressure on the collet lock nut should be increased to almost stall the drill motor.
    4. Increase the drill motor power to about half rated RPM, and, again, gently pinch the collet lock nut, with equal pressure from the thumb and forefinger, to tighten the collet lock nut, until the drill motor almost stalls.

Run out measurements, (measured before 988 holes, and after, to demonstrate stability):

  • Tip of motor shaft run out, (RS-390H motor): not measurable on 1 mil graduated dial indicator. (Motor shaft end play about 0.5 mil., with fore/aft finger pressure.)
  • Collet shaft run out: less than 1 mil. (This is the same as the spindle run out specification on most commercial drill presses.)
  • CNC bit tip run out in free air, running at 6V ~ 11,000 RPM, (i.e., not touching anything): less than 10 mils.

The latter measurement was made by gently descending the CNC bit onto scrap PCB material copper, and allowing the bit to scratch the copper, (but carefully not making any hole-just scratching the copper surface,) and measuring the diameter of scratched circle with a USB microscope. Of interest is the apparent lack of bit walking.


scratch.png

Figure XXIV. Photograph of copper scratch made by the CNC bit tip run out

Figure XXIV is a photograph of the copper scratch made by the CNC bit tip run out of the drill press. The calibration ruler small tics are 0.1mm. The diameter of the scratched circle is about 8 mils., smaller than the drill diameters used in DIY PCB development. The CNC bit will self align to the center of this circle to make the hole.


Striping the PCB, Rationale:

99% Pure SODA ASH (Sodium Carbonate Anhydrous, Washing Soda) (2 lb) is inexpensive since so little is used. A fresh, (as opposed to spent from the developer process,) can be mixed in hot tap water, too.

Note that the striping process is nothing more than an intentional over developing of the remaining photo resist on the PCB-which removes the negative photo resist.


Soldering the PCB, Rationale:

A temperature controlled soldering iron, (for example, Stahl Tools SSVT Variable Temperature Soldering Iron Station,) is highly recommended. Set the minimum temperature that the user is comfortable with. In selection of a soldering iron, verify that replacement tips are available, and preferable that the soldering iron uses "industry standard" tips.

Solder should be 60/40 0.031", (for example, Kester Pocket Pack Solder 60/40 0.031" 0.50 oz. Tube,) for PCB through hole components.


License

A license is hereby granted to reproduce this design for personal, non-commercial use.

THIS DESIGN IS PROVIDED "AS IS". THE AUTHOR PROVIDES NO WARRANTIES WHATSOEVER, EXPRESSED OR IMPLIED, INCLUDING WARRANTIES OF MERCHANTABILITY, TITLE, OR FITNESS FOR ANY PARTICULAR PURPOSE. THE AUTHOR DOES NOT WARRANT THAT USE OF THIS DESIGN DOES NOT INFRINGE THE INTELLECTUAL PROPERTY RIGHTS OF ANY THIRD PARTY IN ANY COUNTRY.

So there.

Copyright © 1992-2017, John Conover, All Rights Reserved.

Comments and/or problem reports should be addressed to:

john@email.johncon.com

http://www.johncon.com/john/
http://www.johncon.com/ntropix/
http://www.johncon.com/ndustrix/
http://www.johncon.com/nformatix/
http://www.johncon.com/ndex/



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