Too much heat during reflow can force solder out of a BTC.

FIGURE 1 shows examples of solder beads after reflowing bottom termination components (BTC). The beads are related to placement force prior to reflow, where the solder paste deposit is displaced away from the pads before reflow soldering. It is uncommon, but solder beads have also been seen coming from the package itself due to excessive heat during reflow. Solder beads or balls on the side of packages and close to the board surface are related to paste printing, paste volume, stencil design, PCB pad size, placement force or reflow, and can easily be demonstrated.

The target style of the x-ray tube impacts magnification, resolution and quantity.

In last month’s column I explained the impact a transmissive or reflective target style of x-ray tube will have on the available magnification of an x-ray system. The difference between the two target types is shown in FIGURE 1. Not just the magnification is altered by the choice of target, however. The focus, or resolution, of the tube, as well as the flux, or quantity of x-rays, that the tube produces will also be affected. This is caused by the x-ray tube settings.

When diagnosing print problems, don’t overlook substrate support.

Substrate support is an important, yet often overlooked, element of the screen printing process. Sure, tooling is top of mind when all necessary parts of a new PCB assembly are being developed. But once it’s in the printer way down in the print nest on the table, we tend to forget about the tooling block. I suppose this out-of-sight, out-of-mind mentality is why manufacturers often point to more obvious, visible components of the printing operation as the culprit when the process shows inconsistency. Surely it must be an issue with the squeegee, the stencil or the board fabrication, right? Well, sometimes that’s the case. In many instances, however, a resolution may be as simple as a look at your tooling; something could have changed, or maybe it’s been incorrect from the start.

If the tooling isn’t manufactured properly or has been altered during production, printing inconsistency is the result – either across the board or from board to board. Paste volumes may be noticeably different in various areas of the PCB or panel; one corner may be just fine, and another has too much or too little material. This dynamic could be the first clue tooling is the cause. If the problem were an improperly manufactured stencil, for example, the issues would more likely be consistent across the entire board. Tooling errors can be extremely focused.

Trade conditions bring “rain” to everyone. Focus on the customer experience.

As I write this, no relief is in sight in the supply-chain constraint situation, and the US is beginning a trade war with China. I’m reminded of a story my grandmother told me when I got my first marketing position after college. Nana worked at one of Miami’s largest department stores in the days when department stores had huge budgets focused on attracting shoppers via user experience rather than reduced prices. This was the era of department store “wars” for market share, where people would line up outside a store to wait for the doors to be unlocked any time a good promotion ran. Nana had just finished executing her first big fashion promotion campaign with ads in TV, radio and the local papers. She saw this as her “make or break” moment in terms of developing credibility in her new position. As she drove to work the morning of the event, it began to pour. Distraught at the negative impact this would have on shopper traffic, she went upstairs expecting to find an equally disappointed boss. Instead, he looked at her and said, “Cheer up Thera, it’s raining on Burdines and Jordan Marsh, too. And, we have the best ad campaign.”