Bob Jacubec asked: What is the proper storage of SMT ICs; are there any guidelines or standards to use? If moisture absorption is a problem with plastic parts, is the standard practice to bake assemblies or parts prior to reflow? What are the baking requirements? Our in-house stores personnel won't break down the sealed outer packs as supplied by the IC manufacturers (they'll issue ICs in quantities as supplied by the IC manufacturers, approx. 100 or 200 parts each). As a result we have opened partial packs of parts remaining in the manufacturing area. Thanks. ************************************************************ Our typical build is 5 to 10 boards of a given design. We assemble one, (first article), and a couple weeks later finish the build. The logic behind this process is to prevent us from populating boards until the design is proven. This means we are ALWAYS in the position of storing parts that were originally supplied in sealed bags. I have heard as many opinions on how long parts can be stored without baking prior to assembly as there are people I have talked with. Since I recently "Popcorned" several thousand dollars worth of parts by relying on these opinions and my personal prior experience instead of real knowledge, I STRONGLY recommend that you learn a little about package molding materials and die attach methods. Armed with this information you can be sure you are getting adequate information from your IC suppliers to help you determine which parts are most likely to need baking and which parts will be more tolerant. The general notion that only THIN Quads, TSOPs and the like require baking is only part of the story. Leadframe plating and overmold materials play a big role in just how resistant your parts may be to moisture absorption induced delamination and cracking during reflow. I was recently assisted by a gentleman named Gans Ganeshan, formerly of Motorola's Advanced Packaging Development Center. There are many papers which discuss this issue in the 43rd and 44th ECTC Proceedings. You may find the following two papers especially helpful. Gans Ganeshan and Howard M. Berg: Model and Analysis for Solder Reflow Cracking Phenmomenon in SMT Packages. _Proc. 43rd. ECTC*_, 1993, pp. 653-660 Gary L. Lewis, et al: Role of Materials Evolution in VLSI Plastic Packages in Improving Reflow Soldering Performance. _Proc. 44th. ECTC_, 1994, pp. 177-185 *(ECTC) IEEE Electronic Components and Technology Conference Gary P. --- Gary D. Peterson _/_/_/ _/ _/ _/ SANDIA NATIONAL LABORATORIES _/_/_/ _/ _/_/ _/ _/ P.O. Box 5800, M/S 0503 _/_/ _/_/_/ _/ _/ _/ _/ Albuquerque, NM 87185-0503 _/_/_/_/_/_/ _/ _/ _/_/ _/ Phone: (505)844-6980 _/ _/_/ _/ _/_/_/ _/ _/ _/_/_/_/ FAX: (505)844-2925 _/ _/_/ _/ E-Mail: [log in to unmask] _/_/_/ *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************