Issue link: https://iconnect007.uberflip.com/i/745476
56 SMT Magazine • November 2016 Figures 9–14 show some examples of reli- ability issues that can be introduced during the assembly and test stage. If you are lucky, this issue will fail at electri- cal test. However, if the stress just makes the sol- der joints weak, the problem might not show up until the product is in the field. In automotive applications, electronics must operate in wide range of conditions. Under stress, the weakest part of the design will surface. Once a PCB has been analyzed for issues that affect reliability, a scorecard can be made to summarize the findings. At this point, you'll want to assign appropriate weight to each fac- tor because some issues are more critical or cost- ly than others. A PCB is constructed of thousands of ele- ments, each of which can lead to failure in the field if not constructed in an optimal manner in relation to the other features. Remember, the reliability of the "custom" component is af- fected not just by the components on the top and bottom side of the PCB, but also the cop- per features throughout the PCB and the pro- cess means used to construct the PCB. If you can analyze the potential effect each of these elements has on reliability while you are in the design stage, you will improve the reliability of your end product. SMT References 1. Bosch Design Requirements for Automo- tive Electronics, 2006. 2. A Practical MTBF Estimate for PCB Design Considering Component and Non-Component Failures, IEEE. Patrick McGoff is a market development manager at Mentor Graphics Corp. HOW TO IMPROVE PCB RELIABILITY Figure 12: Too many ICT test points within an area will stress the solder joints in the area. Figure 13: Insufficient heel dis- tance and even the ratio of heel-to-toe distance can cause a weak solder joint. Conversely, too large of a pad for a device can cause a dry solder joint. Figure 14: Placing breakaway tabs too close to SMD pads can result in damage to the solder joint when you separate the PCB from the panel. Figure 15: The PCB scorecard will summarize your findings that can affect reliability.