Good testability depends on the design

Quality control is essential for a solid end product. But almost all errors in electronics production only reveal themselves at the end of the process. Peter van Oostrom, Division Manager Test and Measurement at Romex, explains during his E&A webinar what to pay attention to, especially during the design phase.

By: Dimitri Reijerman

“What can go wrong during production?” says van Oostrom. “Quite a lot. And the influence of the design of the printed circuit board on contactability is great, because the product must be tested for quality at the end of the journey. In order to properly test the PCB, a process that must be done carefully, it is necessary, for example, to apply test islands. These islands must be large enough so that probes can make reliable contact with the printed circuit board.”

According to Van Oostrom, these are fundamental matters during the design phase: “If a designer does not take testability into account, for example forgetting to create test positions, then you cannot reach them with an electronic test device. This means you cannot verify whether a product functions correctly. Of course you can connect the product to see if it works, but if there is a defect you will have to perform many actions again. That is not desirable. So after assembling a printed circuit board, you want the whole thing to be tested as thoroughly as possible, so that you can install a properly functioning product, put it in a box and send it to the customer.”

During the day his webinar on Thursday, September 30 Van Oostrom elaborates on this in more detail: “In my presentation I will talk about the entire assembly process. The bare printed circuit board comes in, solder paste is then applied to it with a screen printing machine and the components are placed on it. The whole is 'reflowed' in a soldering oven. Ultimately you have a soldered copy at the end of the production line. But anything can go wrong in this process. A short circuit may occur or there may be no solder in certain places, components may be placed the wrong way around. To prevent this, you must carry out inspections between each production step. Once you have finally completed all intermediate control steps in your production line and you know that everything has been properly assembled, you still need to perform an electrical test. That's what we do Romex, we supply the test systems to perform such tests properly.”

Van Oostrom explains how the checks work: “If something is defective on a PCB, you want to be able to reason back and measure in the diagram which component contains the error. You do this with a pin bed, a 'test bed' of springy contact pins. These pins make contact on the bottom of the printed circuit board at the places you want to measure. For example, to determine a certain value of a component or by measuring whether a microprocessor or a memory chip delivers the desired signal. And sometimes you still have to program a processor with the right software. This all happens in the last step of the assembly.”

Not everyone is aware that a mistake can be costly, he says: “Small development companies that develop electronics products in particular are not always aware of the entire production process. So they don't know what could go wrong. And they often do not see the costly consequences of such a mistake, such as the costs of repairs. This certainly applies if you have larger series produced by an EMS. In principle, an EMS knows nothing about your product. In order to be able to produce and test it properly, good communication with the EMS, as early as possible in the development process, is very important to increase quality.”

Mistakes made before

“Most larger companies have made all the mistakes in their existence. Certainly the step from conventional technology to surface-mount technology was a huge step. Components became smaller and smaller, but also the spaces on a PCB. As a result, test tooling has also become increasingly complex. But thorough testing is required, especially in the automotive sector and the medical equipment market. Ideally, a test probe should be placed on each connection between the components to verify it.”

At the end of his presentation, Van Oostrom will discuss the test software: “In addition to a brief discussion of the production process and the different test methods, I also discuss the tooling and creating the right design. So the design must be good to be able to do a decent test at all. Too often I see that test islands are made too small because designers see them as an obstacle or unnecessary. Sometimes they are so small that reliable contact with a test probe is no longer possible and it therefore occasionally sticks next to it and thus carries out an incorrect measurement. Moreover, such a small surface area makes the test tooling much more expensive. That's not handy."

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