PCBA Test Process - Page 1
Forum section: electronics / general

author: lowderd
author_rank: Newbie
timestamp: June 28, 2018, 04:09:19 pm
content: Hello!I'm currently working on defining the test process for the PCBA's in a medium volume (10K-50K) product. I'm leaning towards the following:- AOI on every PCBA (duh)- AXI on every PCBA with BGA's- Functional Test on every non-trivial boardFrom talking with the CM, they're pushing to implement ICT on several boards, my biggest issue with this is that the boards are lacking testpoints on a lot of nets, resulting in test coverage of 45%-50% on the PCBA's they would like to implement ICT on, this leads me to think that we should stick with only performing a Functional Test, instead of spending additional capital on ICT fixtures.My main questions are:- How useful is ICT if a majority of nets aren't accesible?- Should I fight to implement a new board revision with additional testpoints to improve ICT coverage?- Is Functional Test enough for mass production?Any recommendations or advice is welcome!Thanks!

author: Nauris
author_rank: Regular Contributor
timestamp: June 28, 2018, 05:04:48 pm
content: Quote from: lowderd on June 28, 2018, 04:09:19 pmIs that really necessary?QuoteTrivial boards can have faults too...QuoteFunctional test + special test firmware to do as much self testing as possible would be my first suggestion. ICT is that kind of solution you can put together without much engineering so contract manufacturer likes to suggest that. It is questionable how much faults it detects that a well tought functional testing doesn't see. I would not use it but of course it depends heavily on what kind of board you are testing...QuoteFor normal commercial/industrial use, sure

author: Siwastaja
author_rank: Super Contributor
timestamp: June 29, 2018, 06:20:13 am
content: Properly designed functional test should and could detect basically everything that the bed-of-nails or probing test would, plus a lot more. After all, if you test each and every feature, what's there left for the user to find faults at?Neitherof these test reliability issues due to poor solder quality, contamination, etc. I guess it's AOI and random xray or destructive sampling for one every 100 units or so for that.IMHO, testpoint probing ICT is overrated (it's so easy to just suggest such automated, catch-all, off-the-shelf solution), and I believe that a combination of AOI and well-designed functional testing finds the real-world issues much better. Functional testing has the largest scope.For example, I designed, outsourced the manufacturing, and production tested myself a batch of fairly complex boards with an STM32 MCU and an I2C acccelerometer. That particular oldish STM32 MCU has a notoriously buggy I2C implementation, and the code had all kinds of workarounds to get the prototypes working reliably. Youwould expectthat once the code for such digital MCU peripheral works (and the signal integrity on the prototypes is OK), there couldn't be software-related surprises when just producing more of the same.But, strangely, in about 20% of the boards, the I2C sensor was nonfunctional. Of course I first suspected the Chinese soldering of the miniatyre LGA part, but nope, it was in software. Adding extra reset-turn-back-on-sequence as defined in errata sheet foranother MCU of the same family(not the affected device itself - I always read the errata!), all units were working.Only functional testing revealed this.