Hi Steve and TechNet - I have had a several folks ask me to provide a further explanation the " "flux only" will have lower solder joint life than a BGA reflowed with solderpaste". If you look at many of the solder joint life prediction models, you will find that the solder joint height has a significant impact on overall solder joint integrity. Take a look at IPC-D-279, Appendix A 3.1, you will find the Engelmaier-Wild model and the solder joint height influence is fairly easy to see. If an operator reflows a BGA using solder paste, you will get more solder volume and therefore a slightly increased solder joint height. With that being said, the BGA solder joint life will be better but maybe not necessarily required for a product use environment. As many of the TechNet responses have shown, it is common practice to use "flux only" reflow and meet the requirements of many IPC Class 2/IPC Class 3 use environments with no issues. Rockwell Collins has used "flux only' practices for many years and is just now transitioning to the new dip-able solderpastes for both increased solder joint reliability and ease of rework procedure. Rockwell Collins will be publishing a paper on the reliability of BGAs reworked with a dip-able solder paste process in the near future. The dip-able solder paste is not a new thing - many folks in the wafer bumping technology have been using it for years. Werner gives a much better explanation of the impact of solder joint height than my simple attempt. Hope this better explains my comments. Dave "Steve Kelly" <[log in to unmask]> 06/03/2009 03:33 PM To <[log in to unmask]> cc "'TechNet E-Mail Forum'" <[log in to unmask]> Subject RE: [TN] BGA-113 package Thanks everyone for the excellent feedback. Interesting information. Regards Steve Kelly From: [log in to unmask] [mailto:[log in to unmask]] Sent: June-03-09 2:50 PM To: Steve Kelly Subject: Re: [TN] BGA-113 package Hi Steve! Yes, you can reflow a BGA with "flux only" and not use solderpaste. Just remember that solder joint integrity is a function of the solder joint height. A BGA reflowed with "flux only" will have lower solder joint life than a BGA reflowed with solderpaste. And lower life doesn't not necessarily mean bad - just lower. The resulting BGA solder joints may be perfectly acceptable for the product use environment. Good Luck. Dave Hillman Rockwell Collins [log in to unmask] Steve Kelly <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 06/03/2009 11:10 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to Steve Kelly <[log in to unmask]> To [log in to unmask] cc Subject [TN] BGA-113 package Hi All, We have a rigid flex that has a BGA-113 (microstar BGA) package to be mounted to it. The routing in this area on the top layer leaves me with .0005 of soldermask clearance from the edge of the BGA pad and .003 distance from the edge of the soldermask to the nearest track- in other words I have .0035 of clearance from pad edge to next track assuming a perfect etch and perfect soldermask registration. Having rooted around Texas Instruments web site I believe that it may be possible to reflow this BGA without adding solder paste to the pad - just letting the ball collapse do the attachment. If my scenario is correct I could open up the soldermask and not have too many concerns about bridging between the BGA pads and the tracks. Any thoughts or comments would be appreciated. Thanks Steve Kelly Steve Kelly (PLEASE NOTE NEW E-MAIL ADDRESS) (416) 750-8433 (work) (416) 750-0016 (fax) (416) 577-8433 (cell) --------------------------------------------------- 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 -----------------------------------------------------