Design007 Magazine

28 The PCB Design Magazine • August 2015 dles. The angle of the grind would determine what was presented in the cross-section. I once experienced this type of out-gassing. When I worked for a board shop in New Eng- land (which will not be named), we had a spe- cial team that was supposed to move critical orders through the shop quickly. The team had a critical job, but they wanted to go to lunch when the boards were in the middle of the wet process line. They figured that it would be all right to hold the board in the sulfuric acid bath while they went to lunch. They were gone about an hour. This worked well for the copper because a mixture of sulfuric acid can reduce copper oxide and will not attach metal copper, but it was not so good for the dielectric. The team returned and finished the process. The next day the boards were delivered to the customer. During assembly, they noticed that when the boards were soldered, a geyser of white smoke would push up through the solder and continue to smoke for as long as the soldering iron was ap- plied to the hole. I'll never forget this condi- tion because, under a microscope, these holes looked like little erupting volcanos. The two animations in Figures 4 and 5 de- pict both types of HWPA. Figure 4 shows a stress-relieving HWPA forming. Please note that the outgassing is not as severe in this type of HWPA and the coupons survived for hundreds of thermal cycles. The animation in Figure 5 shows the severe out-gassing of stress-inducing HWPA. The hole wall is deformed to the point that the copper is pushed all the way to the other side of the hole. The failure is an interconnect type of failure. These coupons failed in fewer than 100 thermal cycles. PCBDESIGN FAILURE MODE: HOLE WALL PULLAWAy continues Figure 3: Horizontal cross-section of stress- inducing HWPA. Figure 4: Animation depicting stress-relieving HWPA. Click to view animation. Figure 5: Animation showing out-gassing due to stress-inducing HWPA. Click to view animation. Paul Reid is retired, but open to suggestions. To contact him, click here. reid on reliability

• Front Cover
• Featured Content — The War on Process Failure
• Table of Contents
• Column — Fighting the War on Failure
• Feature — Kelly Dack and Mark Thompson Unite in the War on Failure
• Feature Column — Failure Mode: Hole Wall Pullaway
• Feature — Mentor Graphics Helps Bridge Gap Between PCB and RF
• PCB007 Highlights
• Feature Column — Failure May Not Be an Option, but Sometimes It's a Reality
• Short — Physicists Develop Ultrasensitive Nanomechanical Biosensor
• Column — Stackup Planning, Part 3
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• MilAero007 Highlights
• Column — A Brief Overview of High-Frequency Laminates
• Article — Training the Next-Generation Engineer: When Does it Begin and End?
• Top Ten Recent Highlights from PCBDesign007
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