Board fabrication messup, board house experiences? - Page 1
Forum section: electronics / projects

author: jakeypoo
author_rank: Regular Contributor
timestamp: January 13, 2012, 04:49:36 pm
content: Howdy.I've just had a batch of boards come back from a board house that I've only used for a few small runs (<100 boards). This last batch (300 pcs) had a nasty problem and all my through holes AND vias were plugged with solder. These were unpopulated holes for a 0.100" header, and some standard size vias.Last batch of these boards were fine. I think the wave solder bath wasn't up to temperature, and this was a manufactuting mistake. I was told that I should have specified that holes should not be filled, but I've never had this problem before. Considering vias were plugged as well, I think this was their fault.I have only been in the electronics game for about 2 years, so I would love to get some feedback about who is at fault here.Anyone have similar experience? What is the standard protocol for these things?

author: ciccio
author_rank: Frequent Contributor
timestamp: January 13, 2012, 10:02:29 pm
content: I had a similar problem with the last batch of PCB received from my usual supplier:- some holes (both components pins and vias) were closed by some metallic component (tin?)- all through holes had a smaller diameter than specified.I complained with the supplier. They analyzed the defective boards and told me that the problem was the result of a non compliant (defective) HAL (hot air leveling) process.HAL (or HASL)http://en.wikipedia.org/wiki/HASLis a surface finishing process, that uses molten solder and hot air knives: if the temperature or the air pressure are too low most holes remain full of solder.I returned all the boards and (I believe) they were able to repeat the process and I got on-spec boards.

author: Short Circuit
author_rank: Frequent Contributor
timestamp: January 13, 2012, 10:34:19 pm
content: I'm not sure about via's, but for regular holes (say 0.5-0.6mm and up), it is normal practise that the holes are open, without specifically asking for it.Better yet, you don't have to ask for it, because formally, they have delivered a board without holesRegarding open via's, I think its reasonable defence that you should specify this, in which case they'll probably use a chemical plating process.The amount of tin on the walls of the holes may vary somewhat, but tolerance of of drillsize vs pindiameter is usually enough to compensate for that.

author: jakeypoo
author_rank: Regular Contributor
timestamp: January 14, 2012, 04:27:10 am
content: Quote from: ciccio on January 13, 2012, 10:02:29 pmI don't believe this was a HASL problem.I should add that these boards were assembled with SMD and Through Hole components. This means that they did a solder stencil -> populate SMDs -> reflow oven then populate thru-hole components and wave bath.If this problem was during reflow or HASL, the thru-hole components would not have been able to be populated.

author: Neilm
author_rank: Super Contributor
timestamp: January 14, 2012, 11:10:23 am
content: Once (many years ago) I got some prototype boards at work that had several nets shorted together. The PCB manufacturer had screwed up.The real kicker is that all the PCBs were supposed to have been tested.We only found out the problem after we had populated the PCBs, and four of the chips were precision trimmed resistor networks - £30 each.Neil

author: Rufus
author_rank: Super Contributor
timestamp: January 14, 2012, 11:46:21 am
content: Quote from: jakeypoo on January 14, 2012, 04:27:10 amYes you should have added that in the first place because forced to make an assumption most people assumed you were talking about bare PCB manufacture not PCB assembly.As for unpopulated holes and vias filling with solder I would fully expect that from a wave solder process. If you didn't want vias filled they should have been tented and if you didn't want unpopulated holes filled you should have specified it and provided artwork for peelable solder mask (and expect to pay for the additional processing).

author: Short Circuit
author_rank: Frequent Contributor
timestamp: January 14, 2012, 02:06:10 pm
content: Quote from: jakeypoo on January 14, 2012, 04:27:10 amAh, misunderstanding, I was writing about bareboards.For PCB assembly & soldering, then yes; you should specify that holes must remain open. For some holes (like obvious mounting holes), common sense dictates that they should remain open, but unpopulated TH component holes get filled usually. Similary, if you'd need then filled, you need to specify that also.What Rufus said; either peelable solder mask, or manually applied masking, either semi-liquid latex or kapton tape

author: ciccio
author_rank: Frequent Contributor
timestamp: January 14, 2012, 03:38:37 pm
content: I did not read carefully the first post, so I understood that the holes were plugged in the bare boards.I understood "board house" as the manufacturer of the bare boards, not the assembler of the populated boards.The problem I reported was on bare boards.If I don't want the wave soldering process to close some holes, I specify this to the assembler, who protects the holes with a solder masking component (as Short Circuit writes above).Best regards