need help with DIY: low-budget accurate double-sided PCB manufacture ..no UV?

tuk · Aug 13, 2011

reading through guides and opinions on pcb manufacture; and would like some help filling in the gaps or hearing alternative suggestions

required:
cheap
accurate
double sided
repeatable
quality

so thinking of going with photo-resist board and artwork film,

The guy in this YOUTUBE guide makes a good looking board using 'a common 13w cfl bulb' (2m:50s) ...but nearly all the other guides(including datasheet) says it has to be a special UV light..so what gives; will any high-street 13w cfl do the job or does it have to be a special kind of UV?

I don't own a printer but have quite a few printer services around locally...is one type of printer better than another?

The artwork pocket method for double sided exposure, looks prone to slipping and mis-alignment to me, so I'm considering the following steps:

using a picture frame(see utube guide above)...

remove protective cover & expose component side
drill the 3 guide holes
remove protective cover on solder side
align solder artwork using drilled holes
expose solder side
develop and etch

Other suggestions for aligning double sided artwork or general comments welcome?

proposed materials:
Jetstar Standard and Jetstar Premium inkjet artwork films **broken link removed** or **broken link removed**
Fotoboard 2 Photo-resist FR4 DATASHEET
Seno Liquid Developer **broken link removed**
Seno PC145 Ferric Chloride Liquid Etchant **broken link removed**

Thanks for reading.

FvM · Aug 13, 2011

CFL is basically O.K. for exposure.

For alignment of two-sided PCB artwork, I suggest to assemble both films with adhesive tape to a bag. On one or two sides, the bag should be smaller than the PCB substrate, so it can be fixed to it. If done properly, the pack can be even turned over in the exposure frame without losing the alignment. But preferably, you have an exposure frame with two glas sides, that can be turned over without opening it.

tuk · Aug 13, 2011

thanks for the reply...

FvM said:
For alignment of two-sided PCB artwork, I suggest to assemble both films with adhesive tape to a bag. On one or two sides, the bag should be smaller than the PCB substrate, so it can be fixed to it. If done properly, the pack can be even turned over in the exposure frame without losing the alignment. But preferably, you have an exposure frame with two glas sides, that can be turned over without opening it.

sry I don't get this part & hate doing things I don't understand; the 2 sides can be aligned perfectly using the bag method but inserting the pcb surely means some degree of misalignment..as the bag sides are pushed further apart ...doesn't it make more sense to do each side separately and drilling guide holes to ensure perfect flat alignment?

DeepOne · Aug 13, 2011

Quite well got print lazer printer on glossy watertight paper for jet printer - glossy layer is stuck to toner and creates strong covering. However possible this passes not with any watertight paper for jet printers.

jpanhalt · Aug 13, 2011

I also use photoresist to make PCB's and agree with FvM that most fluorescent bulbs will work. You will have to do some experimentation to get your exposure time and etching conditions correct. The resist contains a photosensitizer that allows them to work at wavelengths of light longer than one might guess for the simple chemistry of the resin.

As for the "bag" to get double-sided boards, the error is very small. A similar process is used to duplicate rivet positions on overlapping aluminum skins and is called a "strap duplicator." Here is a drawing (not to scale) to illustrate using some typical dimensions in cm. The board is cross-hatched in red. In drawing A, the bag is perfectly aligned, and the error is obviously quite small. In drawing B, one sheet is shifted. The error, assuming a right triangle, is about 1 mil. I typically use a full width (8.5") for the duplicator on a board that is 2.5" or so wide. I suspect the error from stretch in the plastic is greater than the error in alignment.

John

FvM · Aug 13, 2011

The method worked well for me at times, when I have been etching two-sided PCBs myself (most recently 10 or 15 years ago). Of course, the alignment quality depends on how the "bag" is made exactly. A better alignment can be achieved by punching the films and fixing it with register pins, which is a classical method used by PCB manufacturers.

Aligning a film to drilled holes without register pins is rather inaccurate in my opinion.

tuk · Aug 13, 2011

thanks for the info guys, do you think plastic artwork sheets are best all round for what I'm trying to do ...what about tracing paper and the like?

FvM said:
A better alignment can be achieved by punching the films and fixing it with register pins, which is a classical method used by PCB manufacturers.

Aligning a film to drilled holes without register pins is rather inaccurate in my opinion.

just read through a diy guide on this using map pins ...I might give both the bag and pin methods a whirl to see what's involved ...although the pin guide suggests etchin/exposing 1 side at a time for some reason which seems a bit more tricky and extra work

why not?...

fix first artwork to side of pcb
drill reg holes through artwork & pcb
insert pins in holes and flip over
drill reg holes through second artwork
add second artwork to other side of pcb; impaling on reg pins for alignment and fix to pcb
remove pins and expose both sides
etch

METHOD #1: PIN REGISTER
The "One-Side-At-A-Time" Technique

If using our 1/2oz copper-clad laminate, you'll have a very fast etch, normally under 1 minute if you use our newest "Contact Etch" technique (see "No Etching Tank?" in the current sub-menu). Because of this very fast etch capability it begs the question of why spend 5 minutes or so registering artwork when you could do one side at a time and be done with both sides in less time!

You will need 2 items for this technique before we start:

Matching diameter "Map Pins" and "Drill Bit" - as close as a perfect match as you can get
Avery Label - or similar "paper-type" tape)
Acquire a small box of short "map pins" from your local stationary store. Measure the diameter of the pin's shaft and obtain a drill bit to match. The tighter the tollerance the better. You want the pins to be secure into the holes drilled through the laminate board to register your print outs.

Lay the "open-donut-hole" pattern face down over the copper board without any alignment concerns other than being some what centered over the board. The board will be trimmed later. Transfer this image as per normal by TIA applicator or iron and add the GreenTRF. When ready to etch, cover the bottom with conventional "shelf liner" paper (available from any hardware store) and etch the board in the usual manner. When done, remove the shelf-liner paper and drill out the reference marks you have designated as your alignment "targets" (albeit donut holes, pads or targets). Now drill the second artwork page in the exact same places. (If you use Carbide bits, you'll have extremely clean holes though the transfer paper.)

Clean the copper surface of fingerprints that have surely gotton on the previously cleaned copper. Insert the pins through the back of the paper and into each respective hole in the board so the paper is lying flat over the raw copper surface. Using a paper-type tape (Avery label or thin masking tape) secure the top and bottom of the print to the board. Remove the pins and process the board through the TIA applicator or iron as per usual. Just before etching, add the shelf-liner paper over the first etched side. Press securely over the drill holes to ensure etchant does not seep into the holes and propogate onto the etched side. When done, remove the liner sheet and using a new, dry paper towel wet with Acetone, remove all toner and GreenTRF.

At this point you're basically done. To prevent oxidation to the cleaned copper you'd normally want to tin-plating the copper and possibly add a white silkscreen layer and our new solder mask techniques.
www.pulsarprofx.com/pcbfx/main_site/pages/tech_support/register_2x_pcb.html

Nick C. · Aug 14, 2011

One 'gotcha' with the photo method is that ordinary window glass can block much of your UV light.
My setup (many moons ago) used clear acrylic sheet instead of glass. And as far as a light source,
a standard fluorescent under-cabinet light fixture ($15 at Home Depot) works just fine for home use
(well, at least with the Kinsten material I used to use).

Another tip is that whenever you change your setup (exposure lights/presensitized boards/etc), do
a test board to make sure what the correct exposure time should be. This will save you a lot of grief
in the future. This is similar to what you would do when developing/printing your own photographs.

What I did was to print out a series of numbers, equally spaced, on a transparency sheet using my
laser printer.

1 2 3 4 5 6 7 8 9

Now lay that strip over your presensitized PCB and cover all but the '9' with a sheet of cardboard.
Expose for ten seconds, then slide the cardboard to the left to uncover the '8' and '9'. Keep exposing
for another ten seconds and uncover the '7', '8', and '9'. Keep working your way to the left until you
expose the entire strip for ten seconds. (Don't hold me to these times - it's been several years since
I've used this technique. Start with what the PCB manufacturer recommends and work outwards from
that). Now develop and etch, and you will get an idea of what the right exposure time is for your setup.

Of course developing/etching time/temperature/material are all variables as well, so you might have to
do a little bit of experimenting. I'd suggest wasting some PCB material on these tests so you get the
process dialed in before you start trying to make your project. It will be a lot less stressful that way.

Good luck with your project!

jpanhalt · Aug 14, 2011

Ordinary window glass is fine for making PCB boards with the presentized boards that are available today.

Source: Ultraviolet - Wikipedia, the free encyclopedia
Ordinary window glass passes about 90% of the light above 350 nm, but blocks over 90% of the light below 300 nm.[6][7][8]

One does need to be careful not to get UV-blocking glass, tinted glass, low-E glass, and glass with any reflective coating. But then, such glass is not "ordinary window glass." N.B. The fluorescent light bulb you will be using is made of ordinary glass.

Pure acrylic (a.k.a. Plexiglass, Lucite) can also be used, but because its formulation is very easily modified, one may unknowingly get material that has a UV blocking agent in it. That is often done in anticipation that the acrylic will be used for picture frames or windows for which blocking UV is an advantage. Anything with the slightest yellow tint will block the UV wavelengths you need.

This article describes the UV properties of various formulations of acrylic. See pages 3 and 4 particularly for the spectral absorptions: **broken link removed**

As mentioned previously, you will need to make test runs to get your exposure correct. I use two opposing arrows (triangles) that just touch at the points.

John

FvM · Aug 14, 2011

Ordinary window glass is fine for making PCB boards with the presentized boards that are available today.

Yes. Glass won't work with pure UV C sources, e.g. low pressure mercury vapour discharge lamps, as they are used for EPROM erasure, but with acrylic neither. Window glass is used for most standard exposure frames, also for screen or offset printing, using blue to UV A wavelengths.

need help with DIY: low-budget accurate double-sided PCB manufacture ..no UV?

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