Assessments are needed for new parts and alloys to ensure reliability.

Solder joint failure on QFNs may occur for several reasons. These include:

• Differential thermal expansion of board and component.
• Flexure or drop testing substrates.
• Conformal coating/encapsulate expansion.

The rate at which solder joints have been found to fail is due to thermal expansion of the solder alloy, joint height, temperature range, size of package, and size of die in package. These reasons for failure also relate to the product design and substrate thickness. To confirm product reliability for a specific environment, engineers need to undertake reliability assessments on any new component types and alloy combinations. The SEM images (FIGURE 1) were taken after 1000 cycles between -55° and 125°C with no apparent visual damage. Microsections did detect some level of cracking in selected joints. It’s fair to say many of these packages are used today, but when the package size increases, often the basic reliability questions are not being asked.

Calculating costs to move physical gear is much simpler than predicting inefficiencies of new locales.

As I write this, a trade deal with China that will eliminate the tariffs appears to be in development, but China is continuing to talk tough.

Imaged solder mask is preferred to filled vias to reduce voids and volatiles.

The QFN examples in FIGURE 1 compare soldering with and without through vias in the center pads. The difference is the correct paste stencil design and the use of solder mask around the vias. This prevents solder lost to the vias and has been shown to reduce void formation during reflow with convection and vapor phase soldering without the need for a vacuum.

Warm market winds continue to lift the SMT market, based on the activity at the annual SMTA trade show.