The Benefits of Applying Flux Directly to a Micro BGA


Reading time ( words)

In order to make sure we were getting good wetting between the pad and the BGA, we decided to section one PCBA horizontally and the other vertically. Horizontal sectioning helped confirm the presence of good solder joints and it was possible to see where the ball had flowed around the pad separated by solder resist. In the vertical section, you can see that two balls have detached with the PCB pad still attached. For the purposes of our trial this wasn't a problem and occurred due to the forces applied during sectioning. To avoid this issue occurring again we would look to pot the PCB in a clear resin prior to sectioning.

BGA3_JJS_12May2017.JPG

Left image: Horizontal section showing a slice through the center of the BGA. You can also see the copper pad of the PCB, BGA ball and connection between both. Right image: Vertical section removing the device to leave just the solder balls.

Our conclusions

Applying flux directly to micro BGAs is a good alternative to stencil printing but comes at a cost. Depending on the manufacturer a dip unit and transfer plate can cost anywhere between £13,000–£17,000, compared to a stepped stencil that typically costs just a few hundred pounds. Much depends on the products you are manufacturing and the quantities you intend to produce on a monthly basis. If the volumes are high enough then investment in an automated solution may well be the right decision for you. If, however, you are producing small batch quantities then you may not be able to justify the investment and need to continue trials with different stencil designs and materials.

Hopefully, this blog post has provided a useful insight into just one of the challenges electronics manufacturers face on a daily basis. Although the majority of issues can be overcome through robust engineering and NPI processes, the most effective way to mitigate them is to ensure design and manufacturing teams work closer from the outset.

So, if you're forced to make component changes in the future, we recommend you look at the rest of the board and then talk to your manufacturing partner before committing to materials to ensure your design can be manufactured in a cost-effective manner.

This article originally appeared on the JJS Manufacturing blog, which can be found here.

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