Use partial CT to reveal trace discontinuities at incoming inspection.

In last month’s column, I suggested using x-ray inspection equipment more typically used for the investigation and quality control of assembled PCBs to check bare boards ahead of their use in assembly. Such equipment is often already onsite and readily available to the assembler. The benefits of enhanced magnification and resolution this equipment can usually offer toward inspection of representative bare boards ahead of assembly is, I contend, an opportunity to provide additional confidence that all is well in the bedrock of PCBA. Furthermore, the cause of any future issues, if they occur, can be more easily narrowed down to the assembly process, design or components. The example I gave related to the possible issue of poor drilling quality in the board vias and how, in x-ray images, the plating variability can be readily seen, especially if the via is buried within the board and optical inspection is not possible. Variable plating quality, however, such as voiding in the central termination of a QFN (see “QFN Inspection: Don’t Forget the Edge!” December 2018 column), can often be relatively obvious for an operator to see when it occurs in the x-ray image such that if it is not present and all looks consistent and appropriate, then other subtler issues may not be considered fully, or missed entirely.

Powder abrasion is an effective means for removing UV-curable materials.

Should finer solder particle sizes result in better process results? Our work suggests no.

In December we discussed a solder paste material evaluation for printing metric 0201 assembly. In summary, three solder pastes – two type 5 materials and one type 6 material – were analyzed by stencil printing them onto a PCB with an array of different patterns and two different pad designs of 100µm x 115µm and 125µm x 115µm, respectively, with three different component pitches of 100µm, 75µm and 50µm. In the end, the supplier A type 5 (T5) solder paste had the least variability, even with the 50µm interspace. The supplier B type 6 (T6) paste deposits appeared almost over-printed, with large deposit volumes and some wet bridging.

For component placement and reflow analysis, which were carried out on a Siplace TX placement machine and a Rehm nitrogen-capable reflow oven, the best-performing T5 paste from supplier A and the supplier B T6 paste were used. In addition to the original PCB design (PCB 1) containing discrete pad designs without traces, a second test PCB (PCB 2) integrated the same pad dimensions but with the addition of a conjoined trace between pads. Our observations were as follows:

Is automotive, not military or space, the impetus behind today’s electronics innovation?

Never say never. Every time I even think of saying “I will never,” something happens that makes me regret it. And yet here I am, once again, admitting to another of those instances of “I will never.”

This time, I allowed my experiences and background to cloud the reality on the ground. I started my career in the shadows of NASA. That great American technological juggernaut began when Kennedy challenged us to land a man on the moon and return him safely to earth. Conceptually, it all seemed so simple. For generations the US government, originally through the military and later with NASA’s help, drove dramatic technological advances by investing in new technology and the materials and processes necessary to achieve them, so that besides filling their immediate needs, those technologies would eventually become commercial standards integrated into consumer products.