With the development of surface mount technology, the mounting density of PCB is increasing very fast, as a result of that, even for PCB with less density, automatic inspection is not only basic requirement, but also commercial. During the inspection for complex PCB inspection, 2 normal ways are nail-bed test and flying probe test.

1 Nail-bed test

This kind of way is using probe with spring to connect with each test point on the PCB. Spring can let the probe withstand 100-200gpress force and to ensure each test point working properly, all the nail probe array together can be viewed as nail bed. Under the control of inspection software, we can program test point and test signal, graphic below is a typical structure of nail bed inspection, inspector can acquire all the information about test point. Although both side of PCB can be tested simultaneously by using nail-bed test method, designer should still consider to install all the test point on the solder side of PCB. Nail-bed test device is very expensive and hard to repair.

There is basic universal array processor constitute by drilled bare board, the distance among each pin center is 100mil, 75mil and 50mil. These pins play the role like probe, and use electrical connector or joint on the PCB to make mechanic communication. If PAD on PCB is compatible with test array, then polyamide film which has been drilled orderly can be placed among them for the sake of inspection design. Continual inspection is through get access to end point of network grid. Since all the networks on the PCB can execute continually inspection, then a isolated inspection can be finished. However the distance of each probe constrain the functionality of each nail-bed.

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