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46 The PCB Magazine • August 2016 a feeling of relief and accomplishment and I am concentrating on other activities. Rather just minor modification, I made a complete face- lift and one chapter becomes two, one on PTH reliability and the other on a new topic of mi- cro reliability. My intention always has been to pay back to the industry, but this became a hefty one even though I am proud of it. I am proud to be able to add the most updated research on PCB reliability. Again, just a con- tribution to technical community with no fi- nancial gain. Q: It has only been a few months since the Handbook was published, but have you received any input from the industry? A: Just this month I received two emails, one asking for a good reference on PCBs and the other one had comments after review of the chapter on microvia reliability, especially on drawback of current coupon testing. Even though I have heard similar comments during IPC Thermal Stress Test Methodology Subcom - mittee meetings, but this is on the stack mi- crovia which is an interesting one and I like to share since it is timely too. Jerry Magera wrote that for stacked microvias, they have observed that opens may occur at temperature above the PCB Tg (glass transition temperature), more typically around 220°C, it stays open through the peak temperature, followed by reconnect/ closure during cooling. They have tested these types of failures to thermal cycling, -40°C to 125°C, and found that such latent defects were undetectable. Solder float tests also does not detect these failures. They also found that cur - rent induced testing is not appropriate for ac- ceptance test and also unable to detect micro- via issues. He recommends that "the current induced test coupons should be used by PCB manufacturers to monitor their process for PTHs." So the two chapters on PCB reliability need to be revisited to include new technolo- gies and requirements when the co-editors de- cided to publish the 8 th edition. I want to send my sincere appreciation to the two well-known coeditors of the 7 th Printed Circuits Handbook for their tireless effort to put together such an invaluable new edition. ____________________________________ Joe Fjelstad Verdant Electronics (Chapters 67, 68, 69, 71) Electronic Assembly… Is it time to remove the "training wheels"? Many children learn how to ride a bicycle by using training wheels— two extra wheels attached to the rear axle to allow them to keep upright as they learn how to ride. The down side of training wheels is that they slow the rider down and impede changes in direction. In many ways, solder is the training wheels of electronic assembly. It slows down manufacturing and impedes the industry's ability change direction when it comes to making products that are better, more reliable and less expensive. However, in order to gain those benefits, as with riding a bike, the would-be user has to exercise balance, discipline and good judgement. To illustrate, consider the following example. Below are images of two electronic assemblies, they are identical in function and were designed by the same designer, Darren Smith [1] , using the same general design rules. Yet as can be seen, one is substantially larger than the other and has twice the number of circuit layers. What makes that possible? Three " Just this month I received two emails, one asking for a good reference on PCBs and the other one had comments after review of the chapter on microvia reliability, especially on drawback of current coupon testing. " THE AUTHORS OF THE PRINTED CIRCUITS HANDBOOK SPEAK