Makerfabs Daily: Problems in PCBA Functional Testing

Makerfabs Daily: Problems in PCBA Functional Testing

December 11, 2020

As a PCBA vendor, Makerfabs deal with more than 100 PCBA projects every month, here is a simple record of problems in our daily PCBA functional testing.

More than 100 PCBA projects Makerfabs dealt with per month, from PCBA prototyping a few pcs to mass production a few thousand. For this amount of projects, there usually many problems we encountered every day, either from project managers/ Production/ Testing… Not to mention those lots of very problems in the customers designing, that we have to check with the customer back and forth.

Here is just a simple record& example for these problems in our daily PCBA functional testing:

1. Testing Problem

Makerfabs helps on the PCBA functional testing, based on customer send us the testing guide, to ensure 100% pass for shipped items. Of course, include the controller programming (PIC/ STM/ FPGA/ DSP/ AVR...)
But for one shipment, named XXX_Receiver, 1000 pcs, that we tested OK and shipped to customers, our customer feedback there about 25 pcs not passed in the application, because of the bad Ethernet connecting. ~Bad!~broken heart

So we have to check the whole story and procedure:

1. Check again the testing guide, if the testing procedure covers the connection testing... Indeed there is…

2. Check the all the testing records, All the testing record OK.
3. Check the testing method in filed about how the worker testing the board. A little differ from the customer’s guide, Makerfabs engineer made a simple testing jig, to speed up the testing, as below:
Then we found the root reason:
1. There the RJ45 connector is somewhat oxidized, some of the connectors connecting not good.
2. To speed up the testing, our worker connected to the RJ45 pads with pogo pins and connected them to a dedicated RJ45 connectors, that is, the on-board connector is bypassed, and not tested.
As got the bottom reason, our solution:
1. Feedback to the RJ45 connector vendor about this oxidation, or consider a new connector;
2. For each pcs testing we insert the Ethernet cable to the on-board RJ45 connector, to testing the connection.

With this testing modification, the same problem do not happen again in the further production.

2. PCBA Quote Problem

For each PCBA customer, there Makerfabs will assign a PM (Project Manager) to serve from the quotation to the final shipping/ quality assurance. There 5 PM now at Makerfabs: Helen, Sabrina, Zeqing, Vivi, and Allen.
In the PCBA quotation step, normally after the PM made the quotation sheet, which is based on the PD(Production Department) investigation& Assessment, there will be another PM to cross-check the quotation, to ensure the quotation OK and proper.

But mistake happens...
Helen’s quotation for the project (xxxkey), a “0” was removed by mistake, just before she sending it to customer. And more, customer paid as the wrong quotation with Paypal. That is, only 1/10 of the PCB value.

We found this mistake as starting the production, and notified to the customer the serious mistake, and suggest to refund (thanks to Paypal) and cancel the order.

We understand this caused our customer’s bad experience, and lucky that, the customer kindly to re-pay the total project, and we proceed the production.

We will never be too careful for the business quotations.

3. Still PCBA Functional Testing Problem

The project of "ctag_xxx" is a 4 layer PCBA, with plenty of BGA/QFN package, a good-design shield for beaglebone. In the testing of it, we got confused by the testing result: only 36% pcs passed the testing, with the customers send testing tools and guide.

After again and again checking & comparing of the pass/ no-pass boards, we do not find any difference with them, so we have to feedback customer about this bad result. Indeed we are nervous about this, this project is designed by our long-term customer, an excellent college team, is there anything wrong we made?

Lucky our custom kindly checked the whole testing, and realized that it may because of the testing method itself. Together, we re-check the signal for many pins, and made some new testing method:

With the updated testing method, Makerfabs tested all the boards, and 100% PASS. Happy our customer replied:

"That's great news. Thank you for all the extra hard work getting these boards over the line. Please let us know if you would like us to pay extra for the additional time which has gone into the testing and we will pay the final balance."

Er, No extra payment needed, our duty for that. Just share our service to your friends. Thanks...smiley
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