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56 The PCB Design Magazine • October 2014 film will result in a very tough, high-reliability thermal cycle PCB. The 2 mil dry film can take the extra copper plating and still give a sharp edge. With the thinner base copper, you etch less and get finer lines and higher yields for free. The super board I mentioned had 1.8 mils of plated copper in the holes. The operator was trying to compensate for an error: One panel out of four had been wrongly laminated with thin base copper of only 5 microns, not the half-ounce copper called for in the build sheet. The plating operator must have measured the copper thickness, and to make it look like a normal board, he plated more copper to com- pensate for the thin base copper that was acci- dentally laminated on. He did not tell anyone and off the panels went for thermal testing. Later, I got a call from our test operator. "Can I take this set off the tester? It's been on for three weeks and it's not even close to failure, and I need the machine." So, the big secret is this: If you want your PCB to survive more thermal cycles, just add more copper to the plating in the holes or mi- crovias. It's as simple as that. See you next month. PCBDESIGN Bob Tarzwell is a PCB consul- tant who has spent 50 years in the PCB industry, inventing technology and building al- most every type of PCB. He is the co-owner of DB Publishing, publisher of the PCB 101 and Quality 101 handbooks. For more informa- tion, visit www.dmrpcb.com. Dan Beaulieu is a well-known industry consultant and co- owner of DB Publishing. His column It's Only Common Sense appears Monday morn- ings in the I-Connect 007 Daily newsletter. He can be reached at danbbeaulieu@aol.com. Figure 2: red line is a normal 1 oz. copper-plated board; the black lines are 2 oz. copper-plated boards. bob and me TARzWELL'S FIRST—AND LAST—LEAN MEETING continues