Erasing silkscreen, which chemical? - Page 1
Forum section: electronics / projects

author: mcinque
author_rank: Unknown
timestamp: March 08, 2015, 08:05:28 pm
content: I must erase some silkscreen references because I'm going to sell a dev pcb and I want to hide some infos about the components placed (ICs, opamps); I've tried the most common solvents without success...What do you suggest? I can't erase it mechanically.

author: NF6X
author_rank: Unknown
timestamp: March 09, 2015, 12:26:20 am
content: I believe that silkscreen ink has traditionally been epoxy-based, so I would expect any solvent that would effect it would also attack the board itself. I don't know if that's still the case with newer processes.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 09, 2015, 12:30:05 am
content: Anything that will dissolve silkscreen will also dissolve resist and damage the board material.Why would you want to erase info from a dev board?

author: mcinque
author_rank: Unknown
timestamp: March 09, 2015, 12:57:13 pm
content: Because it was a custom PCB I designed for developing a commercial project, with all the infos about the part numbers etc.I have accepted to sell it (not the rights, only it's use), so I'd like to remove any reference to part numbers.Maybe an epoxy based paint would do better?

author: Emil
author_rank: Regular Contributor
timestamp: March 09, 2015, 03:50:51 pm
content: Same topic in this thread:https://www.eevblog.com/forum/projects/remove-silk-screen-from-board/msg533249/#msg533249On the boards I tried it was possible (not easy) to remove the silk screen before I reflowed the boards. After reflowing it was nearly impossible.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: March 09, 2015, 04:05:26 pm
content: As it is obligatory to point out, erasing the silkscreen probably won't do much. If someone wants to clone your board, they WILL. Are you also going to grind the marking off the IC's and use unmarked resistors?

author: Ericho
author_rank: Regular Contributor
timestamp: March 09, 2015, 04:30:44 pm
content: Acetone, or the wife's nail polish remover

author: eneuro
author_rank: Super Contributor
timestamp: March 09, 2015, 04:49:08 pm
content: Quote from: mcinque on March 08, 2015, 08:05:28 pmDid you tried.... DVD laser to burn it?I have similar problem, but need to remove oryginal IC markings and make custom marks on IC to make cloning PCB worth much more work hour$Of course do not want play with lasers without addidional visual camera in custom CNC-I do not believe in laser safety glasses-and maybe even make this process automated with OpenCV-camera recognizes IC and its markings than calculates its position and... burns them with additional random marks to make even more difficult find what kind of IC was blankedIt might work, but we do not like risk refelctions from copper, IC legs, pads, etc, so no way ONLY controling this process using visual camera and watching on LCD screen and do not play with those silkscreens in a way like in this quite decent power red laser from DVD-RW burner

author: nitro2k01
author_rank: Frequent Contributor
timestamp: March 09, 2015, 06:44:17 pm
content: Quote from: Ericho on March 09, 2015, 04:30:44 pmUnlikely to work. At least the silkscreen doesn't budge on a number of random board I just tried it on now. Maybe if you leave it overnight or heat it, but then you're probably likely damage the soldermask or glue board-metal bonding of traces at about the same time you damage the soldermask.

author: pickle9000
author_rank: Super Contributor
timestamp: March 09, 2015, 07:00:37 pm
content: Any paint stripper that contains petroleum distillates. It can destroy the mask as well. It will also remove gloss which can be touched up with nail polish.

author: ijchan223
author_rank: Contributor
timestamp: March 09, 2015, 08:27:03 pm
content: Unless you are going to scrub all the chips it is pointless to do so.

author: DanielS
author_rank: Frequent Contributor
timestamp: March 09, 2015, 08:55:37 pm
content: Quote from: eneuro on March 09, 2015, 04:49:08 pmUnless you are doing something obscure, the component layout around most ICs kind of give away what the chips are even before looking at markings. People who do reverse-engineering and know their parts reasonably well will quickly see through most attempts at misleading labeling. Beyond that, once you have identified the general function and positively identified some of the key functional pins, the rest is just a matter of looking through parts catalogues to find what fits.If I was doing reverse-engineering for a living, I would build a database to cross-reference chips and pin functions so I can quickly weed out potential candidates in nearly no additional time for off-the-shelf parts: trace the chip's connections for reverse-engineering, enter positively identified pins as a database filter, and by the time I am done tracing to lift component values, I should be down to a short list of likely interchangeable parts.The only way to make something nearly impossible to reverse-engineer is to use (semi-)custom ASICs or CPLD/FPGA/MCU with encrypted firmware - it does not matter if you reverse-engineer the PCB when you cannot get the parts or the software to make it work.

author: mcinque
author_rank: Unknown
timestamp: March 09, 2015, 09:23:08 pm
content: Thank you for all the suggestions, but at the moment none of them worked.I don't know what kind of silkscreen the PCB manufacturer uses, but it's very tough.I will try with some graffiti remover.Quote from: ijchan223 on March 09, 2015, 08:27:03 pmWho's so dumb to hide silkscreen part numbers and leave them on the chips?Quote from: nitro2k01 on March 09, 2015, 04:05:26 pmOnly the IC's.Quote from: nitro2k01 on March 09, 2015, 04:05:26 pmQuote from: DanielS on March 09, 2015, 08:55:37 pmGuys, I'm not trying to hide any holy graal secret, I know that everything can be reverse engineered.This is only to avoid serving a free meal... it's nothing else than what many manufacturers do; for what reason some hardware manufacturers spend a lot of money in laser etchers to erase chip part numbers when anyone with a proper knowledge can reverse engineer them? It's only to discourage the beginners and to avoid easy servicing.

author: qwaarjet
author_rank: Regular Contributor
timestamp: March 10, 2015, 01:52:37 am
content: Why not just pot the board after assembly with opaque epoxy. Covers everything, make reverse engineering hard as hell since you have to remove the epoxy without destroying the underlying pcb to even probe signals let alone ID chips.

author: miguelvp
author_rank: Super Contributor
timestamp: March 10, 2015, 02:00:25 am
content: Run a new batch without the silkscreen?

author: eneuro
author_rank: Super Contributor
timestamp: March 10, 2015, 10:47:04 am
content: Quote from: DanielS on March 09, 2015, 08:55:37 pmSetting lock fuses in AVRs probably will not prevent from reading binary flash, while as I know there are services available to read MPU protected code for a few hundred$I used to use customized (compiled) software for each MPU with unique ID, so reading flash and programming the same device in clone product will not work (ok. it will run, but...much worse performance to give advantage and credit to oryginal official inventor), since MPU has passed during compilation constants specyfic to manufactured PCB hardware, so If someone will try just copy pase it won't work on another similar MPU since he will never match exactly the same hardware configuration, so to make this MPU code usabe in clone a lot of disassembling needed, which in practice means it will be cheaper write new code than dissassemble existing software to findout where in the code those significant constants are and how another PCB hardware have to be tested to obtain proper values