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54 SMT Magazine • November 2016 mechanical drill process. Clearly, you will need to maintain greater clearance to avoid creating a short or open in the backdrill process. Many issues can prove to be problematic during the assembly and test stage as well. Most of the top 50 contract manufacturers world- wide perform some design-for-manufacturing (DFM) as a service. While this is valuable, each of them may approach the subject differently and thus you get a variety of responses. For ex- ample, some may show you where you can im- prove yield, cost, and reliability, while others may merely look to see that your design can be manufactured by them. One way to identify po- tential reliability issues with a design is to ana- lyze it using software that will assign a severity indicator to each instance. After all, reliability is a probability of failure. Software tools that can pinpoint what issues are more likely to cause a failure can be quite helpful. HOW TO IMPROVE PCB RELIABILITY Figure 8: Using software to identify potential reliability issues with a design and that assigns a severity indicator to each instance is helpful. Figure 9: Connecting pads with different trace widths can cause the component to tombstone during reflow because of the variance in surface area. Figure 10: Resistor tombstoning caused by a difference in cop- per area on connecting pads. Figure 11: Traces under a no-lead device may cause the component to rock, or teeter- totter, because of the difference in height of solder mask and solder paste as the PCB goes through the reflow oven.