Sodium meta silicate for pcb repair - Page 1
Forum section: electronics / repair

author: pcm81
author_rank: Regular Contributor
timestamp: September 12, 2025, 11:13:30 pm
content: Was not sure if this thread should go into pcb design or the repair section, so here it is.Recently i bought a microscope and have been playing with pcb rework... just practicing on junk pcbs.One thing i have been working on is a qfp package removal, replacement. And of course in the process of dong so i ripped off some pads. They look to be 0.25mm in width. And of course all the flux and alcohol started to dissolve the phenolic that the pcb is made of. Its just 2 sides board, so no layers in the middle. I have been looking for glues to fill the voids left by scraping out the soft phenolic under the ripped pads. I am basically trying to run a 0.2mm magnet wire in place of the pad, but now have soft phenolic that makes a hole like half way through pcb. Tried flooding it with super glue and UV curable epoxy, but they are still getting soft from flux and alcohol. So it occurred to me, why not try to flood those holes with sodium meta-silicate, water glass, let it cure and then just grind accurate size channels for magnet wire?Google says sodium meta silicate is corrosive??? what do you guys think???

author: tooki
author_rank: Super Contributor
timestamp: September 12, 2025, 11:34:10 pm
content: Quote from: pcm81 on September 12, 2025, 11:13:30 pmUhhh… what?? Aside from the fact that most PCBs these days (including practically all double-layer boards) are fiberglass epoxy composite, not phenolic, neither epoxy nor phenolic are readily dissolved by flux or alcohol!!

author: pcm81
author_rank: Regular Contributor
timestamp: September 12, 2025, 11:49:16 pm
content: It is a pcb from the control panel of an epson printer. I am guessing the cheapest they could make...

author: pcm81
author_rank: Regular Contributor
timestamp: September 12, 2025, 11:58:12 pm
content: The solder masked regions are indeed not affected by flux or alcohol, but the board under ripped pads got mushy and easy comes out like mashed potatoes or goo.

author: Jonny
author_rank: Regular Contributor
timestamp: September 13, 2025, 01:36:54 am
content: Without seeing it, sounds like the board might be too far gone. Depending on the pin pitch I'd be looking at dead-bugging the chip. Stick it to board upside down and run wires from pad to traces. It's only a printer so no need for some advanced restoration, unless you're up for a challenge

author: coppercone2
author_rank: Super Contributor
timestamp: September 13, 2025, 04:02:38 am
content: use epoxy. its what they use. a good epoxy is resistant to that.keep in mind copper does not glue as good as their unless you black it (sodium chlorite and hydroxide)

author: Psi
author_rank: Super Contributor
timestamp: September 13, 2025, 04:10:14 am
content: I've seen people try to learn board repair on PCBs that are so old they are totally different to modern PCBs. Old PCB can be terrible with regard to tracks/pads lifting easily and the core material can be totally different.A photo of your board would help us tell if your board is typical or not.

author: jpanhalt
author_rank: Super Contributor
timestamp: September 13, 2025, 09:52:42 am
content: From the description and the author's use of "phenolic," it is probably FR1 or FR2. The resin in them is thermoset and cannot be melted and reformed. When it appears to melt, it is actually undergoing thermal decomposition. I suspect where pads lifted, it was overheated to the point of decomposing the phenolic to some undefined goo, perhaps with charing.There is no fix for that. Some solvents* may remove it or it can be removed by scraping or grinding. Any bond with epoxy or other adhesive would be questionable. It doesn't need to be completely removed, but enough, non-damaged FR1 or FR2 must be exposed for good bonding.The best advice has already be given. Practice on modern PCBs.*Sodium metasilicate is quite alkaline. It might actually remove the goo and leave a bondable substrate after washing with water. I haven't tried that..