application of solder mask onto PCB

Thread Starter

harinikrishna

Joined Apr 3, 2020
30
hi
Happy new year.
Hope you are doing good.
We are trying to make our own PCB board.
We are using UV curable green soldemask ink .
We followed 2 methods to apply the solder mask
1) screen printing method
2) a method from youtube (
)

For screen printing, ween we tried to cure the solder mask for 4 hours under UV light and for our surprise, the ink did not even cure a bit.
In 2nd method, We got better results but when we tried soldering components, the hot air is creating air bubbles onto the mask.
Can you help us in knowing what is that we are doing wrong to not achieve a good solder mask on our board?
Thank-you
Warm Regards
Harini Krishna
 

jpanhalt

Joined Jan 18, 2008
10,917
What did you use for a UV source? Was it UVA (e.g,, wavelength > 315 nm or so) , UVB, or UVC (germicidal)? Apparently, the material you bought comes without decent instructions. From what little I could find, one should use UVA. Some things to consider:
1) Too much UV exposure can be as bad as too little. Too much can cause secondary reactions and destroy cured material. Too little may not cure enough.
2) If the material is designed for UVA, using UVC (or UVB)can be as bad or worse than too long an exposure. UVA-cured polymers probably have a photosensitizer in them that effectively starts a free-radical reaction. UVC can destroy that "catalyst" as well as the desired products from that reaction.
 
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Thread Starter

harinikrishna

Joined Apr 3, 2020
30
What did you use for a UV source? Was it UVA (e.g,, wavelength > 315 nm or so) , UVB, or UVC (germicidal)? Apparently, the material you bought comes without decent instructions. From what little I could find, one should use UVA. Some things to consider:
1) Too much UV exposure can be as bad as too little. Too much can cause secondary reactions and destroy cured material. Too little may not cure enough.
2) If the material is designed for UVA, using UVC (or UVB)can be as bad or worse than too long an exposure. UVA-cured polymers probably have a photosensitizer in them that effectively starts a free-radical reaction. UVC can destroy that "catalyst" as well as the desired products from that reaction.
HI,
We are using a light source of the wavelength of 385nm. It is the same setup that we are using for our photoresist exposure in the PCB making process.
I am attaching the image of the ink that we are using to apply the solder mask.
do you suggest to change the light source?
Can the same light some for exposing the photoresist film not be used for the solder mask?
 

Attachments

jpanhalt

Joined Jan 18, 2008
10,917
I searched for a datesheet for that product without much luck, I did find some information:

https://www.fishgaga.com/p/UV+Lique...er+resist+green+ink_2980377.html#.X_LqPFVKju8

Exposure intensity/time, recommended film thickness, and lamp "metal halide":
https://www.tamuracorp.com/file.jsp?id=17803

Your exposure wavelength of 385 nm is within the range produced by metal halide lamps. I would do some experiments. Cover a blank board with a piece of opaque material, like aluminum foil, expose a strip, move foil, expose 1st and second strips, move foil and repeat. That will give you a series of exposures, for example 1,2,3...n minutes, if each period is 1 minute. There may be a post (or pre) exposure heat cure. I can't determine that from the links I posted.

Without decent instructions, though, you are left guessing. My working assumption would be that all of the green photo-curing resists are similar. Thus, I would search for a procedure for a resist from a dealer in your country that would be required to provide the equivalent of a material safety data sheet and technical datasheet

Data: typos
 
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Janis59

Joined Aug 21, 2017
1,245
I am using the finger-smearable photo pasta from China. Exposition is done by 20 pieces 3W LEDs from distance of 15 cm for 8-11 seconds long. LEDS are kind of 390 nm. Only problem is to mear the pasta in well uniform layer. Tried to use the 3-ton book-press with screw - full fail, one side is thicker than other. Then I constructed a vacuum plane with suck-in holes at perimeter and mild film to press it. That works very well.
 
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