Auditors can help improve processes, but certifying quality is another story.

Writing in the August issue of PCD&F, Peter Bigelow says quality programs should ensure quality, not hamstring ingenuity. “Micromanaging a supplier by approving or certifying processes the customer is not familiar with will ultimately hamstring their supply base and add unnecessary cost and time, thus defeating the purpose of the approval or certification,” he concludes.

I believe outside auditors or consultants can help improve yields, lower costs, shorten cycle times, and so on.

When it comes to application, less is more.

Self-adjusting paste deflectors save solder paste and simplify cleaning.

Regular readers of my column are certainly well aware of the challenges around print process variability and the impact even small changes can have on printing results. With a procedure as dynamic as printing, ensuring every input is spot-on is critical to a good outcome, especially in the age of miniaturization. This holds true for what many would consider even the most minor of details: the paste deflector.

Every squeegee our company supplies to a manufacturer comes with a set of paste deflectors. These very simple pieces of formed metal are mechanically connected to the squeegee body with two bolts, and their job is to keep the solder paste material from moving outside the print area. They act like dams to keep material within the angle of the squeegee. While paste deflectors play an important role in reducing material waste and maintaining material integrity, they don’t come without challenges. Setting the height of the paste deflectors is a manual operation, and getting them just right can be tricky. If the deflector is set a bit too low, when the squeegee comes down to meet the stencil and pressure is applied, the deflectors will actually grind into the stencil. At worst, the deflector can punch a hole through the stencil, but it will most certainly leave a trail or coin the stencil if set even slightly too low (FIGURE 1). To avoid damage, operators often set the deflectors a little higher to permit a margin of error. This approach, however, lets paste run underneath the gap, and enables material to run up the outside of the squeegee, which can also introduce process problems.

Using x-ray in a nonstandard way is useful in process development.

Here are three different examples of paste after placement or prior to through-hole component insertion. The images shown here are not necessarily defects, and it may seem strange to use x-ray to inspect paste deposits after printing, but it can be very useful for in-process control and ideal for preproduction runs.

FIGURE 1 shows a QFN/LGA. In this case we are interested in the placement force and the degree of paste displacement on the center pad under the device. Normal practice is to look at the degree of paste variation between printing and placement. It’s even more important when there are multiple rows of outer terminations.