Hi Dave, What was the PCB finish? If it is HASL the voids will be much smaller then if it ENIG. You can also use microvia between 1-3 or playing with the laminate thickness. Regards, Gil -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman Sent: Thursday, February 25, 2010 5:43 PM To: [log in to unmask] Subject: [TN] Suggestions on Making BGA Voids Hi gang! Ok, I have a fairly crazy request for suggestions on how to make BGA voids. First here is the background - Dr. David Bernard (Dage), Dave Adams (Rockwell Collins) and I are working on a collaborative project to investigate the thermal cycle solder joint integrity of BGA components. We are attempting to produce data which the IPC JSTD 001 committee can use to revise the 25% maximum void criteria. Despite public rumor, this current IPC JSTD 001 void requirement is based on actual IPC Class 3 field equipment results submitted to the committee several years ago. However, BGAs have changed in both size, pitch and solderball diameter since the creation of the void criteria thus the reason for collaborative project. We have a test vehicle which contains BGAs at 0.5mm, 0.8mm and 1.0mm pitch with each having a corresponding larger solderball diameter. We have put uvias in the BGA pads to "create" voiding. Great plan, figured we had it made- however, after running the test vehicles thru a standard reflow process (this effort is focused on tin/lead right now) we find that we have an average void size in the range of 0-5%! My production process folks are very proud of that result but it doesn't do our voiding investigation much good (you can imagine the look I got when I told them they didn't make enough voids greater than 25%). I know that a number of the Technet community have tried to accomplish this voiding task with only mild success (i.e. Bev Christian, Martin Wickham, etc.). My Technet request is - do you have any suggestions on how to increase the solderball void size without causing a biased negative impact on the solder joint quality? I can obviously make some huge solderball voids (such as pouring Doug's Diet Mt. Dew on the test vehicles) but the overall quality of the solder joint would not be representative of the real world product. Thanks in advance Dave Hillman Rockwell Collins [log in to unmask] ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. 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