[log in to unmask] on 04/16/98 07:11:19 PM Please respond to [log in to unmask]; Please respond to [log in to unmask] To: [log in to unmask] cc: (bcc: Brad Kendall/Hella North America Inc.) Subject: [TN] Gen: BGA Hi everyone, I am a contract manufacturer who is in process of implementing BGA placement. Our P&P machines are capable of placing them so that is taken care of. However, I need information regarding: ***I read Jim's response and he is right on the money with his responses, I just have a few more pointers to add for you. I implemented BGA about 2 years ago at my previous employer. 1. BGA rework stations(manufacturers, avg cost, user friendliness) ***I bought and used the DRS-22 from Airvac also. It works very well and the service and support are very good. 2. temperature profile of BGA reflow if differ from other types of components(e.g. QFP, PLCC) ***I did take an engineering board and drill small holes under the BGA and pass the thermocouples through them and checked the temps under the BGA. I did not have to adjust my profile much. If you have a good convection reflow oven it will heat properly and you will have no problem getting good reflow on the entire part. 3. X-ray inspection(what industry trends, if any, are currently being used to inspect BGAs(100% x-ray inspection, little less, or none) , are there facilities that will X-ray them for cost, and if so what is avg cost..) ***I did not buy or use X-ray. If you are doing 50 mil pitch BGA and you use a 26 mil non-soldermask defined pad and tent your vias, you will not have bridging. It is actually difficult to make a bridge on this design due to the large space between pads. If you get into micro BGA, then consider it. As Jim said, X-ray does not work well with opens, in fact I did not find a system that could detect opens. The BGA process is so robust if you follow the right steps and use the right equipment, you will not have defects. If you want to have some prototypes analized get ahold of IBM in Endicot. They have a die test they perform. We sent them boards and they performed this test and returned them with a nice report complete with pictures of the joints and all. They test for opens, shorts, cold solder joints, etc. and report back what you can do to fix it. The only problem, you need a deep pocket to afford this. But we did it and liked the results and it saved us money on capitol equipment. ***I encountered 2 problems that caused me some pain. Number 1- BGA is MUCH more moisture sensitive then any part you have delt with in the past. We used BGA's that had been open more then 2-3 days and the corners would curl right up and have opens after reflow. You must open them and use them immediately (or reseal them in inert atmosphere.) The second thing is wave solder. If you wave solder your boards after through hole insertion, monitor you BGA with a profiler and see what your temps are under the BGA. We would develop opens after wave solder. I found that the center of the BGA (trapped heat) was getting to reflow temps and the solder joints would open or crack. These are the joints X-ray could not find, but IBM did. I had die cut Kapton tape squares made and in prewave these were applied to the underside of the PCB under the BGA. This dropped the temp under the BGA during wave solder by 30-40 C. We were running about 50% yield at first (BAD), but after finding and fixing these problems yields quickly went to nearly 100%. The other thing to watch for is test having BGA's reworked because they say there is a problem under the BGA. They want to default to this because they cannot see the joints. At first they just took the boards to repair and they changed the BGA and then they would find the same problem and come to me. I would help them out and we would end up finding the problem was not the BGA. I finally got to where any BGA rework had to come to me first and 99.9% of the time we could find a problem somewhere else on the board and the BGA was fine. Just be aware that test will be very quick to blame the BGA because the cannot probe its pins. Good luck. Brad Kendall Hella Electronics I am on a fact finding mission, so any input would be greatly appreciated. Thanks in Advance. Tom Han Ardent Systems, Inc. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. 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