Using Screenprinting for Soldermask - Page 1
Forum section: electronics / general

author: fatalelieberi
author_rank: Contributor
timestamp: October 14, 2020, 04:06:22 am
content: Hi,I am figuring out how to make a good soldermask for my homebrew PCBs. I've seen a lot of videos using Mechanic UV curable soldermask paint and they use a transparent film to spread out the paint below it. However, from the video, it is difficult to make it even so I am thinking of using a regular mesh for screen printing for spreading the paint. Actually, I tried it once using a T150 mesh, however it didn't work well. The paint was too thick to flow through the mesh. So, there are two ways that I can think to solve this, using a less dense mesh or thinning the paint. However, I don't know what kind of mesh that I need to get and also solvent that can be used to thin the paint. If you guys have tried this method, can you share with me some tips? Thanks a lot.

author: nisma
author_rank: Regular Contributor
timestamp: October 14, 2020, 07:54:27 am
content: There exist three methods.Legacy screenprinting, you apply and UV cure the mask with inkjet printed layout and then clean with Hugh pressure water jet cleaner. Second is screenprinting whole PCB and UV cure with cheap laser engraver and correct laser diode washing them off the pcb before doing optional thermal curing.Third is laser printing direct thermal transfer (disable fixer unit) and after screen printing or applying the coat with blade and partially curing remove the underlaying toner with acetone. The print legend is usually applied with UV curable inc using inkjet printer for CD, no need to modify them and please use yellow and not white color as white clog the nozzles and need throughput, it don't survive more as 3 days of inactivity. If you use CD printer you could print directly to pcb coated PCB with photographic emulsion. Laser toner works too for print legend either as transfer or ink printed and dust box.

author: Mark
author_rank: Frequent Contributor
timestamp: October 14, 2020, 08:48:51 am
content: For soldermask try the Dynamask dry film stuff.You can find small pieces on eBay. I have a roll of it and it is still good many years later.Apply it using a GBC Fusion 300L laminator (A4 size), then laser print your mask layer onto an acetate sheet and expose the film for around 60 seconds under a strong UV light.

author: Fred27
author_rank: Unknown
timestamp: October 14, 2020, 08:52:01 am
content: I can also recommend Dynamask. I've also got a fair bit of it, as I decided to buy a whole roll shortly before deciding I couldn't be bothered making my own PCBs any more.

author: fatalelieberi
author_rank: Contributor
timestamp: October 14, 2020, 01:25:35 pm
content: Quote from: nisma on October 14, 2020, 07:54:27 amThis is what I am going for. But, I cannot screenprint the whole PCB using the UV curable soldermask. It's too thick to go through my screenprinting mesh. Do you know what mesh size I should buy? Also, my plan is that after screenprinting it, I will dry it, maybe using an oven or a heat gun, then finally expose it to UV light with the mask artwork on it. Last, the parts of the soldermask that don't get exposed will be cleaned using an alcohol or oil-based solvent.Quote from: Mark on October 14, 2020, 08:48:51 amUnlucky me. It is rather difficult to find it in my country. Also, in eBay, it is listed with a price of ~350K IDR + Shipping of 150K IDR (~35 USD). It is almost 5 times more expensive than buying a 100cc UV curable soldermask. I think I will leave out this one. Thanks for the suggestion anyway.

author: nisma
author_rank: Regular Contributor
timestamp: October 14, 2020, 03:04:42 pm
content: You must check the datasheet of the soldermask. Traditional require 50t mash but ldi soldermask require 120t and extreme hard plastic squeegee with backplate, otherwise it is not printable. Please take care of comparing mesh numbers, 50t equivales to 120 mesh from memory, 100t to 255 mesh.