Component mix is another issue, Freescale, for example, in their LGA application notes has a target solder volume of 7000 mil^3 and a min of 4800 mil^3. Trying to get to the min with a typical 6 mil stencil would mean overprinting the pad somewhat @ their recommended pad diameter. A thicker stencil may not be an option depending on the pitch/size of other parts on the assembly. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. Sent: Wednesday, March 19, 2008 9:23 AM To: [log in to unmask] Subject: Re: [TN] LGA Reliability Actually, I am in agreement with Werner on LGAs. It is another one of those "it depends" issues. Larger LGAs with arrayed terminations on the bottom of the package are susceptible to process constraints such as the amount of solder deposited on the pads. If you can print enough solder volume to essentially replace the missing solder balls, then you improve the reliability. Even if you use a standard 6 mil thick stencil you end up with very flat solder joints that have very little compliancy to take up the difference in the CTE between the LGA package and the PWB. If the pads on the PWB are .030" diameter or larger, I have noticed that the number of extraneous solder balls under the LGA begins to increase when you are trying to get enough solder under the part. On the smaller types of LGAs with only bottom terminations on the periphery, the problems I have been seeing is trying to keep all of the solder bricks uniform enough so that when they go into reflow all of the terminations are wetted. Sometimes one or two of the pads have a little bit less solder, and no physical contact is made between these shorter bricks and the LGA pads, because all of the rest of the bricks are holding the part up. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /* Sent: Wednesday, March 19, 2008 8:20 AM To: [log in to unmask] Subject: Re: [TN] LGA Reliability Hi Phil, The devil is in the details-however, 2-to-2.5mils standoffs = 2-to-2.5mils solder joint height are of concern even with small delta-CTEs [I am not even going near the cleaning issues]. With large thermal slugs, these packages may also be thermally non-symmetric, which means that they warp out-of-plane both during soldering operations and operation with any kind of power dissipation. Ask them if their "reliability claims" are based on IPC-9701 testing. Werner ************** Create a Home Theater Like the Pros. Watch the video on AOL Home. (http://home.aol.com/diy/home-improvement-eric-stromer?video=15?ncid=aol hom00030000000001) --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------