This might help: -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Werner Engelmaier Sent: Friday, May 07, 1999 4:41 PM To: [log in to unmask] Subject: Re: [TN] Unconnected inner-layer pads The work done for IPC-TR-579, 'Round Robin Reliability Evaluation of Small Diameter Plated Through Holes in Printed Wiring Boards', indicated a small improvement in reliability with the presence of functional and non-functional innerlayer lands. This was NOT a major finding of this study, nor was it a recommendation for the use of non-functional innerlayer lands. The results of the 1997 ITRI Report, 'PWB Hole-to-Land Miregistration: Causes and Reliability', give the same indication (Note: essentially all the failures come from one PWB manufacturer, primarily from PTV barrel cracking, before the test was stopped at about 1100 cycles; the other manufacturers show some interconnect separations of the innerlayer trace from the barrel). The 1997 ITRI report also shows the vast improvement in the quality of PTV structures since the 1988 IPC-TR-579 study. The ITRI study was done with temperature cycling from -65<->+125C; thus, the reliability results directly, on an accelerated basis, relate to the thermal cycling PWBs see in product operation. However, because no excursions were taken to soldering temperatures, where because of being above Tg of the epoxy significantly more thermal expansion mismatch occurs and the epoxy is much softer, the results can not be assumed to be representative of what might happen during PWB assembly. It is during solder temperature excursions that the compressive hydro-static hoop stresses act on the PTV barrel and that surface and innerlayer land rotations occur. These represent quite different loading conditions than -65<->+125C temperature cycling, and may produce different conclusions. CONCLUSIONS: Non-functional lands are not likely worth having, because the small potential reliability gain for high-reliability PTV structures for most applications in not worth the manufacturing difficulties and costs that have been encountered. This is particularly true for todays smaller diameter PTVs. Misregistration and the absence of annular rings are no significant reliability threat to PTV barrels. Assuming, that the behavior during solder temperature excursions is not dramatically different and the PTV interconnect structure survives assembly, misregistration and the absence of annular rings are no significant reliability threat to PTV interconnects. Werner Engelmaier Engelmaier Associates, L.C. Electronic Packaging, Interconnection and Reliability Consulting 7 Jasmine Run Ormond Beach, FL 32174 USA Phone: 904-437-8747, Fax: 904-437-8737 E-mail: [log in to unmask], Website: www.engelmaier.com --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------