More lasers and improved and integrated software have factories humming.

The methods and equipment used to fabricate PCBs are becoming increasingly advanced and centralized. For example, computers, lasers, and AI are ever more common in all areas of PCB processing. In recent years, a considerable number of PCB manufacturers have invested heavily in the integration of the complete shop, with all equipment controlled by one central computer. The interconnection enables quicker file processing, higher accuracy, and improved yields.

One of the most expensive pieces of production equipment is the laser-direct imaging system (LDI), which has made significant improvements in accuracy, speed, quality, and in reducing overall manufacturing rejects. The newer models feature multiple cameras to locate lamination holes, compare them to the original Gerber file, then digitally scale the image to fit the panel. Newer laser imagers are capable of imaging down to 15µm line widths and spaces.

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Is the reflow profile the problem? X-ray can help.

Looking through some recent x-ray images of what I would call “good bad” boards (at least, that is what they are for me, as they showcase “good” examples of how certain “bad” types of failure look under x-ray inspection), I came across a number of different issues that are different from “traditional” BGA/QFN problems mentioned in this space before. To wit, I noted some images showed where solder paste had not reflowed under the devices, and there was the presence of foreign object(s), such as discrete components, trapped under the package.

FIGURES 1 and 2 show how unreflowed solder paste typically looks under QFN joints in an x-ray image. In the magnified view (Figure 2), individual grains of the solder paste are seen clearly, instead of appearing as a typical single smooth continuous joint. The cause of this is probably not an insufficient reflow profile. Rather, it is more likely the board has not been reflowed at all. As it may be desired, or necessary, to x-ray inspect (representative) boards after placement but before reflow as part of a quality control process, it is worth noting this characteristic shape of the solder under the components is different from what would be expected post-reflow.