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August 2017 • The PCB Design Magazine 15 WHOSE FAULT IS THAT BAD BOARD? test needles, so it was concluded that the manu- facturer of the printed circuit board did not per- form the electric test, and some boards passed through, although they were defective. Later, the manufacturer agreed that their secondary facility in China did not do the job properly. Here is the first mistake: The PCB manufacturer did not follow test procedures. The electronic assembly manufacturer did not check the bare boards at the incoming quality department be- cause he had too much confidence in the qual- ity of the Korean PCB company's products. That was the second mistake: The electronic assem- bly manufacturer did not follow test procedures again. He assembled all the boards and after a routine optical inspection, and he concluded that all the components were correctly soldered. The PCB designer did not supply the test pro- cedure for the assembled electronic module, so the EMS company delivered the boards without testing them, except for the optical inspection of the solder joints. This was the third mistake: the customer did not deliver to the EMS com- pany any test method for the assembled boards. The bad boards could not be repaired satisfac- torily, so all the electronic components (a total cost of over US$1,200) were lost. Yet another chain mistake example: When trying to fix the BGA capsule in a socket, it de- tached very easily from the PCB (Figure 3). Of the 12 sockets on the same electronic module, Once, a customer brought in a panel board for assembly. The panel contained 100 pieces arranged in 10"x 10" small circuits for V-cut (Figure 1). In order to print the solder paste onto the board, a stencil had to be manufac- tured. The designer didn't have the Gerber files for the panel, but for a single circuit. However, when the design of the panel was ready, it was observed that the dimensions of the panelized project did not fit the dimensions of the physi- cal panel. We searched for the cause, and we concluded that the PCB manufacturer did not make the V-cut panelization according to IPC standard recommendations; instead, the board shop took the V-cut spacing from the useful area of each circuit. This led to a manual depan- elization in order to avoid component cutting by the depaneling machine. This is an example that can be classified as a fault on the side of the PCB manufactur- er because their operators did not follow the IPC-7351A "Generic Requirements for Surface Mount Design and Land Pattern Standard" rec- ommendations. Therefore, we have decided that our faculty should include IPC standards (especially 2221, 2222, 600, 610, 7351) in the curriculum package for our engineering stu- dents. However, as I used to say to the young student designers, "Do not let others decide for you. Send complete information!" Here is an example of a chain of mistakes featuring three actors. The electronic module was not working properly at the final test made on the customer's premises. After investigating the situation, it was found that certain PCBs presented defects like interrupts and badly plat- ed vias. The boards did not present any trace of Figure 2: The component could have been damaged if a PCB depaneling machine were used. Figure 3: The BGA socket.