Blue soldermask strangeness... or did they mess with my gerbers? - Page 1
Forum section: electronics / beginners

author: stevenhoneyman
author_rank: Regular Contributor
timestamp: September 11, 2015, 02:31:38 pm
content: I've just received my 2nd revision of my little beginner project PCBs from elecrow. I have been going with the "economy" green cheapo option until now, and they've all been exactly as I expected/designed. As this is the second revision I went with blue soldermask to make them easier to distinguish. The trouble is there are some inconsistencies with what I sent and what I received. Nothing critical for a hobby project but if it was me that screwed up I can't figure out why and would appreciate it being pointed out.Some silkscreen has vanished but I blame myself for that as I did fine tune that, clearly a bit too much!So attached we have:A - Green board fpc connector pads, all good with soldermask between padsB - the same connector, unchanged in the design files, no soldermaskC - a different connector on the green board, all pins connected electrically (intended), and soldermask between padsD - same connector on the blue board, no soldermask...now it gets really weird...E - an intentionally bridged solder jumper with no soldermask, which was what I specifiedF - the exact same part used elsewhere on the board... but this one has soldermask between the pads!?! (only this one out of about 10)G - screenie of that area in the gerbers

author: AndyC_772
author_rank: Super Contributor
timestamp: September 11, 2015, 02:45:35 pm
content: You're suffering from 'PCB supplier that thinks they know best' syndrome.It's not unusual for suppliers to make minor changes to a board. For example, if you have extremely thin slivers of solder mask between pads, then they can be quite legitimately removed by the board manufacturer. They'd never fabricate correctly anyway, and if a loose sliver of solder mask breaks off the board and onto a pad, it can cause a fault.You don't, though, and adding solder mask where you've clearly specified that there shouldn't be any, is a complete no-no. I hate it when board suppliers do this kind of thing, there's no excuse for it. It's potentially a big problem in production; if a supplier helpfully "fixes" a bug in a board, then the first thing you may know about the bug is when you've tried and tested the product, decided it's OK, then placed a large production order. If that production order doesn't also include the fix, then you're in big trouble, especially as the bug was actully yours to begin with. You just missed an opportunity to discover and fix it inexpensively.There are two fixes for the problem, neither of which is perfect. One is to put text on each layer of your artwork which says "DO NOT MODIFY ARTWORK IN ANY WAY", or something to that effect, and hope that whoever does the initial processing of your CAD data speaks English and actually cares (neither of which is guaranteed). The other is to use a different supplier, and to let them know upfront that your approval is required for any artwork changes.

author: stevenhoneyman
author_rank: Regular Contributor
timestamp: September 11, 2015, 04:07:39 pm
content: Grr! Oh well at least it's not just me being an idiotI've sent their "QC" team an e-mail, just to see if I get an excuse. I have another board in production which I used some of the exact same library parts as this, but in green colour again, so I'll be interested to see if they manage to get the silkscreen right or not.

author: tggzzz
author_rank: Super Contributor
timestamp: September 11, 2015, 04:14:54 pm
content: Obvious question: what do your gerbers look like inseveraldifferent gerber viewers? If they all look the same then either the supplier has strange gerber tools or they changed the files.

author: stevenhoneyman
author_rank: Regular Contributor
timestamp: September 11, 2015, 04:20:32 pm
content: Quote from: tggzzz on September 11, 2015, 04:14:54 pmFair question. Exactly the same - here's gerber-viewer.com's interpretation:

author: max_torque
author_rank: Super Contributor
timestamp: September 11, 2015, 09:43:31 pm
content: Do you know if both sets of boards actually were manufactured in the same place?Often, something as silly as specifying a different colour soldermask results in your boards getting sub'd out, or sent to a different manufacturing facility. And those different facilities could well have different standards for handling your art work!

author: stevenhoneyman
author_rank: Regular Contributor
timestamp: September 11, 2015, 09:50:58 pm
content: Quote from: max_torque on September 11, 2015, 09:43:31 pmUnfortunately I don't know the answer to that yet - they don't add any serial numbers or markings to boards anymore (well, aside from a marker pen dot on the edge to say it passed an e-test)I imagine it did though - as I said i've previously just used their cheapest special offer green-only deal, whereas this cost a dollar or so more for the choice of any of the standard 6 colours.

author: marshallh
author_rank: Unknown
timestamp: September 12, 2015, 05:10:32 am
content: Some fabs ignore your paste masks and generate their own based on the copper/mask apertures and their best guess, and took it into production. Ask me how i know...

author: stevenhoneyman
author_rank: Regular Contributor
timestamp: September 12, 2015, 09:08:31 am
content: I got a reply from them. They accepted responsibility, apologised and offered a $5 credit (~25% of order value)

author: Stonent
author_rank: Super Contributor
timestamp: September 13, 2015, 10:18:29 pm
content: To be fair, I wonder what the ratio of people who get their gerbers right vs ones that are messed up that the boardmaker correctly fixes.Perhaps they figure it would take them a couple of days of back and forth e-mails to clarify what they could just fix and have a good chance of no complaints.

author: stevenhoneyman
author_rank: Regular Contributor
timestamp: September 13, 2015, 10:24:19 pm
content: Quote from: Stonent on September 13, 2015, 10:18:29 pmI agree it probably saves them time in the long run, and I would maybe have expected them to 'fix' something thatlookedscrewed up (e.g. if I had masked over half an IC or something)...but who removes soldermask from between pins, and then adds some between just 1 of 10 identical sets of pads?!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 14, 2015, 12:52:36 am
content: FYI: for whatever reason, design rules (expansion, positional tolerance) may differ for soldermask colors. (Presumably something about repeatability or how the goo flows in use, or process optimization, or...??) This might explain the removal of slivers in the one case. But doesn't explain the removal of intentionally added openings, which is still their problem.Tim