Most everyone's business relies on optimizing process management so the most reliable product is effected. If not, what's the point. For plastic BGA's, coplanarity always was and still is an issue as is CTE in some applications. Therefore, whatever contributes to a reliable solder joint must be considered. I am a proponent of applying only flux to effect reflow under specified conditions. Short of that, I prefer using "hard" balls in all four corners and reflowing using solder paste thus creating colums that are very forgiving as compliant in light of coplanarity and CTE issues. When not using hard balls, a little drop of epoxy, carefully thought out and applied, does the same job. Not everyone enjoys this concept. Now, we move on to CBGA's requiring paste applications though CTE issues now become equally critical but in reverse in some cases. CCGA's are about as good as you can get because all aforementioned issues are resolved but for one. Where do you get these but from IBM. uBGA's offer considerable advantages on both counts concering coplanarity and CTE matching characteristics. Sure are small though. Ah yes, about solder paste: How can you not use it but in low volume, critical applications where flux will do? Many have stated the obvious as using appropriate design rules. These may consist of using 10% smaller pads than balls then designing stencil apertures to overprint paste 20% - and on it goes notwithstanding aperture shapes as square, diamond, or round. I get along with round very well. Not to get carried away, but you know I will, but considerations for the type connection using dogbones is another factor. Don't do right angles. Go right to the connection and don't forget rework/repair/modification requirements. Now it's time to say and on it goes. MoonMan --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------