Thanks for the elaboration, Paul. It sounds like these would be good papers to read. With what you have said, I believe I sat in on a summary of such an effort presented by Mike on this to pic a year or so ago. I will ping him but it might also be worth while to see if Steve could put them up for the more shy members of the forum. Thanks again and best wishes, Joe In a message dated 7/31/2008 12:42:09 P.M. Pacific Daylight Time, [log in to unmask] writes: Hi Joe, Predicated with the disclaimer "As I understand it" ... what Mike and Jason did was test IST coupons at three temperatures for example 150°C, 160°C and 170°C and establish a curve of cycles to failure plotted against temperature. A curve of cycles to failure at test temperatures was calculated using formulas and methods outlined in the articles. They then calculated the thermal cycles to failure at a lower operating temperature. By performing an accelerated test at high temperature one can estimate the mean cycles to failure at a lower temp. If you know how many thermal cycle the product will see a day; let's say, for example, a computer is turned on in the morning and off at night, giving one cycle a day, you can then extrapolate field life in days, weeks, fortnights etc. This is a very simplified overview of acceleration testing. I suggest you read the articles. We have had good results with customers that have used this method to determine whether to use or reject suspect PCBs. In one case it was decided to accept the risk on a "PWB lot of concern" and the field data confirmed the theoretical projection of MTBF. This method works with simple, well understood, failure modes like metal fatigue. If there are confounding factors like variable copper plating and interconnect separation present in the product, this method is less effective. Once you have good reliable product, acceleration testing to determine field life is the next logical reliability test. Jason Furlong here at PWB or Mike Freda at Sun can better address this protocol, its applications and uses. PWB failure modes of concern include, two types of barrel cracks, two types of interconnect failures, two types of corner cracks, design specific interconnect failures like microvia to target pad cracks, or butt joint failure in sequentially laminated blind capped vias and now, with the advent of lead-free assembly, material degradation expressed as delamination or crazing, to name a few. Lead free assembly and rework routinely reduces reliability by 50% on well made PWBs. The reasons for failure are as varied as the designs, builds, and fabricators used in the industry. Custom PWBs frequently have custom root causes for failure. Paul Reid -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Joe Fjelstad Sent: Thursday, July 31, 2008 12:36 PM To: [log in to unmask] Subject: Re: [TN] Use of QFN devices in high reliability applications Hi Paul Can you elaborate? What is failing and why? What is then the failure rate for lead-free? The same? Lower? Higher? ... I guess I should read the papers ;-) I am interested in getting copies if you have a spare set... :-) Maybe Steve would be so kind as to consent to post them to save you a lot of bother should many others have similar interest Thanks in advance, Joe In a message dated 7/31/2008 6:29:39 A.M. Pacific Daylight Time, [log in to unmask] writes: My sense is that 30% of the reliability failures, in a tin-lead application, are due to PCB failures. **************Get fantasy football with free live scoring. Sign up for FanHouse Fantasy Football today. 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