Manually tenting vias for an existing PCB - Page 1
Forum section: electronics / general

author: gperoni
author_rank: Contributor
timestamp: September 16, 2018, 03:55:17 pm
content: Hello guys,I had this prototyping board made where I incorrectly specified the soldermask clearance and as a consequence I'm having an extremely hard time soldering a 0.4mm pitch BGA (I went the cheapo way and did a 0.4mm BGA with standard PCB techniques). Here is a picture:Is there any way I can apply soldermask to the exposed vias copper, tenting the vias? I figured purchasing some chemical is a better option than re-spinning the board, but I will be going that way as a fallback.Thank you!

author: RoGeorge
author_rank: Super Contributor
timestamp: September 16, 2018, 06:12:40 pm
content: I've seen soldermask for sale (on Aliexpress, for manual made PCBs). Never tested it, but it might work.

author: stmdude
author_rank: Frequent Contributor
timestamp: September 16, 2018, 06:35:23 pm
content: Quote from: RoGeorge on September 16, 2018, 06:12:40 pmYep, it's a thing. I use it every now and then when repairing lifted/corroded tracks. You can apply it with a small paintbrush, or from the tip of a toothpick.

author: rx8pilot
author_rank: Super Contributor
timestamp: September 16, 2018, 07:07:01 pm
content: Look forward to seeing the solution for this. I have been in the same situation and never really found a workable solution.Good luck and share the final outcome if possible.

author: langwadt
author_rank: Super Contributor
timestamp: September 16, 2018, 07:18:59 pm
content: something like this?https://youtu.be/PRO03Jv3qRo

author: JustMeHere
author_rank: Frequent Contributor
timestamp: September 16, 2018, 07:26:14 pm
content: I wonder how well fingernail polish would work

author: rx8pilot
author_rank: Super Contributor
timestamp: September 16, 2018, 08:38:36 pm
content: My guess is that nail polish will be a problem when exposed to the reflow thermal cycle. Potentially bubbling up and having hard to predict chemical reactions.Just a guess though....

author: mairo
author_rank: Unknown
timestamp: September 17, 2018, 12:28:44 am
content: I have done something similar with thin kapton tape, but I only had to do it on two boards. The difficult part for me was to 'master' how to cut the small peaces of tape without touching the adhesive. It work for me that time, but was a lot of work. I did respin the board later on.My solution might be a bit to 'high' for you application tho.

author: janekm
author_rank: Unknown
timestamp: September 17, 2018, 01:17:10 am
content: Since presumably that's 0.8mm between the rows/columns (one row missing from 0.4mm pitch) I can't imagine you'd succeed in filling in the soldermask though it could make for a fun experiment.However it looks like you have left off the pads for some of the solder balls in the BGA? If that's the case your chances for success in soldering it are slim as the non-soldered balls will leave too much space for the soldered ones leading to broken connections.

author: nanofrog
author_rank: Super Contributor
timestamp: September 17, 2018, 02:22:42 am
content: Quote from: stmdude on September 16, 2018, 06:35:23 pmIf I understand you correctly, you're referring toUV curable solder mask. Great stuff for that purpose ^, but I'm not so sure for the OP's situation.Dry film solder maskwould be a better solution IMHO, but I'm not sure if there's sufficient PCB surface area for it to sufficiently adhere.

author: asmi
author_rank: Super Contributor
timestamp: September 17, 2018, 02:07:19 pm
content: Well since you went cheapo - presumably a respin will be cheap too

author: gperoni
author_rank: Contributor
timestamp: September 19, 2018, 06:07:29 pm
content: I actually ordered a respin last Sunday after seeing the first comments as I couldn't find anything suitable on Farnell. I'm also fairly certain manually applying it would have made it difficult for the pads to touch the solder balls... And yes, the respin was cheap!Quote from: janekm on September 17, 2018, 01:17:10 amNo, that's just how the chip is designed. 0.4mm pitch with missing columns. Go figure, it's ancient technology.Also damn, the factory400 guy answered to my thread! I'm a fan!

author: rx8pilot
author_rank: Super Contributor
timestamp: September 19, 2018, 09:04:15 pm
content: Quote from: gperoni on September 19, 2018, 06:07:29 pmHa! Awesome!I am dying to release some videos....I have shot 8 videos that need to be edited but I am swamped. Totally over my limit, working 7 days/week.