PCB fabrication - Dry film resist method - bubble problems

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currentmirror

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Hello all,

This is my first post on this forum. I'm a tinkerer/digital experimenter from Adelaide, South Australia.

I've been using Toner Transfer method for many years and happy with this method for general electronics. But my current application requires 10mil precision (or better).

I've been experimenting with negative dry film from eBay. The processes I am using are good: My exposure is good. Development is good (I can develop without having to contact the PCB, which I am happy about, as many youtube videos show the presenters rubbing resist off the board with their fingers or a brush.. anyway, that aside...). I've tuned up most of my methods and am happy with them.

However, the problem I'm having is when I put the dry film over copper laminate, I get very small bubbles (maybe 5-10 bubbles, 0.5mm in size) appear between the resist film and copper board. I am not able to remove them, and this spoils the job. The laminator I am using (a configurable temperature, a cold roll laminator) has been experimented with by setting different temperatures. I have even put the board through with another on the reverse side to that the rollers have more pressure on the board (Nb/ I am experimenting with 0.032" FR4).

The problem appears to be that the dry film resist is too sticky. It is like sticking shelf liner to a flat surface and getting bubbles, but I would say shelf liner is easier to work with than my dry film. There is no hope of my cold roll laminator removing these bubbles. I am now wondering if my dry film is defective ?

Could anyone tell me what negative dry film (DuPont Riston) should handle like when placed on a copper board ?

Any help/tips appreciated. Thanks

J
 
I gave up making my own boards about 5 years ago. You can now get boards made cheaper than you can but the material. Ten 100x100mm boards, double sided, plated holes, solder mask etc, for $25. I now get them populated as well. Just had 20 boards populated and it cost me ~US$70 with postage. Seriously, look at getting them made.

Mike.
 
Hi CM,
With 44 pin 18LF4620 PICs, I use a laser printer onto transfer film. I'm not sure if it's fine enough for you.
I make quick test PCBs at the moment, then once I have a good design would probably also send for the 'send away' boards, later.
C.
 

The dry film is a waste of time, try the presensitized boards from MG Chemicals. Single and double sided boards available in various thicknesses and copper weights. Super easy, exposure with a cool tone fluorescent bulb. I stopped doing my own a few years ago, but the presensitized boards were the best quality. Everything is a bit iffy below 0.012" because of undercutting while etching and not exposing from a point source of light so I generally stayed with 0.015" or more whenever possible.
For $5/5 boards, with solder mask, silk screen and tinned copper, why bother. Check jlcpcb.com. They are running a discount until dec 25. 5 boards for $2.
 
currentmirror said:
Could anyone tell me what negative dry film (DuPont Riston) should handle like when placed on a copper board ?
Click to expand...

I've not used that particular stuff, but similar things in the past.

Can you try attaching just one edge and holding it away from the board, then slowly pressing it down with a hand roller so it does not touch until it's also got pressure to expel air? That's how a film laminating machine in a PCB manufacturer we used to use worked.

With another adhesive film photoresist (for anodised aluminium dye labelling), the makers recommended method to avoid bubbles was to wet it and the surface with an extremely dilute detergent solution, then use a roller to expel that from the centre outwards & leave to dry.
 
Hi All,

Looks like I've come to the right place for help

I'm experimenting with ISM band pass micro strip filters (yes, I'm a glutton of punishment), but I will not be beaten until I conquer this challenge I gave myself !

Here are some filters I produced at the start of the year using PulseFX toner xfer / Brayer method. The laminate is Rogers Duroid RT5880 (it's like frinkin chewing gum !)

<pic>

Because the Rogers laminate is very expensive (and very hard to source in AU), I'm refining my processes using cheap FR4 for the moment. 0.032" FR4 is what I am playing with now when using the exposure/dry film method.

When you are up at 2.4GHz, if the strips are out by 5mil, it changes the response of the filter significantly. I've made some lovely filters using PulseFX method, but it's not not repeatable for my application.

So, that's why I can't really use some of your suggestions, plus I love the empowerment of making my own. I love the challenge !!

rjenkinsgb . Thank you for your suggestions. I think you might have nailed it with the soap. I didn't think of that. I'll give it a crack, and post up by result

Nb/ I'm not transmitting/emitting. This experiment is purely bench level testing. It was actually part of a customer request years ago, but the requirement has long disappeared, but have taken on the challenge. RF is not my field of training/qualification, but have learnt a lot in the process of experimenting with this technology.

PS/ Some of your manufacturing techniques you guys have posted over the years have been very clever; thinking outside the box. Excellent reading . I'm going to love this site I think.

Cheers J

PSS/ I had an embedded pic, but forum not happy with it. So removed.
 
Hi CM,
I would look at milling machines. If you do, check the error feedback from other customers, before you buy though.
C
 
The biggest problem I see with making your own is the inability to do plated holes. Plus, now I can get surface mount populated I can use 0402s with abandonment. When I had to use 0603 LED they seemed huge. When I had to hand solder (not make the PCBs) I stuck to 1206s.

Mike.
 
I have brother hl 1112e and 10mil is no problem with toner transfer.
but would not go below 7.5mil. 5 mil is risk but works
Do not use foil from ebay etc . Its crap
This resist method is time demanding and hard to do.
I would rather buy pcb from china. If i wanna profesional results.
 
Hi M,
Can vias be used instead?
C
 
Pommie said:
Vias are plated holes and I don't know any way to make them. Even without vias, aligning the two sides is very difficult.

Mike.
Click to expand...
Hi M,
Sorry for the delay!
I have some 1mm hole vias and they are hollow. I use them as vias, and the 'tube' fills with solder once they are soldered.
What do you use plated for and will the vias I describe work?
C
 
Hi currentmirror - welcome to ETO!
I use dry film photo resist with great success. I also do my own through-plating and liquid solder resist (the latter two don't go well together at all though, working on that...)
So anyway, the trick is moisture. The professional way to do it is is like rjenkinsgb said, but professionals have a machine to do the application - trying to do it as an amateur is tricky at best, and often hopeless.
Sounds like your resist is nice and new and fresh, which I find harder to work with. Mine is a bit old and dried out, which is easier because it doesn't stick so well.
Anyway, wet the board before applying the resist, peel off the one side and slap it on. The water will fill any voids and stop the film sticking to itself, however it will stick to the board when it's had the water squeezed out. Put it in a paper carrier when it goes through the laminator, which will absorb the drips.
Depending on the film you have, you might need anything from just breathing on the board so your breath condenses on it (which lends itself more to "peel as you go", to wetting board and film under the tap.
I made an Instructable which covers the subject, you can find it here: https://www.instructables.com/Somewhat-Complete-PCB-Fabrication/ Step 7 is the bit you want.
If you still get bubbles, the official advice is to prick them with a pin, though I haven't had much luck with this. if they miss the tracks, then they don't matter anyway.
 
Thanks for the info throbscottle. I've bookmarked your article. I'll read it tomorrow.

A friend sent me this article a month ago:

Photoresist Dry Film - a New Method of Applying It to Copper Clad

Photoresist Dry Film - a New Method of Applying It to Copper Clad: I recently had a go at using this film to make my own PCBs. It is ideal if you don't have a laser printer or photocopier and therefore can't use the Press'n'Peel (and similar) products. But optimism quickly turned to...
www.instructables.com

Today is the first day in over a month I returned to this. I applied the advice from this article today with good results:

It's an article by a Medical Scientist who uses techniques he learnt in his profession in PCB manufacturing. A very interesting read.

I've been a bit lazy/experimental and not followed his "drying out" guidance (After lightly squeezing out as much water with lilt-free tissue paper, I put the boards into the laminator first cold, and then at 100C) but still get good results. For completeness, I'll try his full method tomorrow.

J
 
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