TABLE OF CONTENTS Tim Williams
The previous chapter's checklist included some items that referred to the testability of the design. It is vital that you give sufficient thought throughout the design of the product as to how the assembled unit or units will be tested to prove their correct function. In the very early stages, you should already know whether your test department will be using in-circuit testing, manual functional testing, functional testing on ATE, boundary scan, or a combination of these methods. You should then be in a position to include test access points and circuits in the design as it progresses. This is a more effective way of incorporating testability than merely bolting it on at the end.
The first test for an assembled PCB is to confirm that every component on it is correctly inserted, of the right type or value, and properly soldered in. It is quite possible for manual assembly personnel to insert the wrong component, or insert the right one incorrectly polarized, or even to omit a component or series of components. Automatic assembly is supposed to avoid such errors, but it is still possible to load the wrong component into the machine, or for components to be marked incorrectly. Automatic soldering has a higher success rate than hand soldering but bad joints due to lead or pad contamination can still occur.
In-circuit testing lends itself to automatic test fixture and test program generation. Each node on the PCB has to be probed, which...
