Issue link: https://iconnect007.uberflip.com/i/1507822
94 PCB007 MAGAZINE I SEPTEMBER 2023 When a PCB customer buys boards untested and does not do a bare board test of his own, it is difficult at best for him to identify defects in the boards. is is usually attempted in a pretest area aer the boards have been loaded with components, and it is complicated by his not being able to see the board under the com- ponents, the possibility of bad components, and the processes such as wave solder that the boards have been put through. Suffice it to say that all but a small minority of defective boards end up being scrapped (components included) with too much time having been invested in them while trying to get them to work. So, no one's the wiser? Probably not for long. Customer Testing Most PCB customers are well aware of the "Japanese Scenario" wherein all components of a product (including PCBs) are tested prior to assembly so there is very little troubleshoot- ing, repair, or rework investment. is is what the customer wants. A second aspect of the scenario is that of process feedback, wherein, when a part fails a test, an engineer immedi- ately researches the cause, and fixes it upstream so it does not happen again. is is what the PCB manufacturer needs to improve his yield. Let us keep both aspects of the scenario in mind and look at what happens when a cus- tomer buys a bare board test system (because the PC manufacturer doesn't have one). is is a self-perpet- uating circle. e circle is detrimental because: • ere is a good possi- bility that the artwork the manufacturer was given to build the boards with, or one of his upstream pro- cesses, is somewhat out of spec. is means that the defective features get included in the boards somewhat regularly. • e manufacturer first learns that a percentage of a PCB run failed when his customer calls to order more, as soon as possible. Scheduling is disrupted by another hot order. • Depending on distances involved, board volumes, and return for credit process- ing delays, the manufacturer may always be one or more runs behind in finding out what went wrong. • Unless the test error printouts attached to returned boards show a blatant correla- tion, research into defect causes requires a time-consuming correlation of errors by hand. e manufacturer probably can- not spare the labor because hot orders are coming through. • e customer test circle is bad for pub- lic relations. e customer sees all process problems before the manufacturer has a chance to rework and alleviate them. • e manufacturer has no control over the customer's testing. Some of the boards being returned may actually be good but were failed because of sticking or bent pins in the test system and fixture. • A testing opera- tion needs trouble- shooting feedback to insure valid test results. A trouble- shooting (and repair) operation needs retest feedback to ensure that repairs are effective. In the customer test circle, there is so much time and red tape between these operations that neither function well.