Wave can definately reflow BGA solderjoints. There are several design and process things you can do to reduce this problem. Design tricks: 1. Use a dumbell BGA footprint. One end of the dumbell is a round BGA SMT pad. The other end is the via pad. Make sure that the trace connecting the two round pads is as narrow as possible. 2. Cover both sides of the connected via with LPI soldermask. 3. Plug the WAVE side of the connected via with a secondary soldermask. Contact your local PCB fabricator to find the best way to do this. 4. Maximize the distance between the BGA SMT pad and associated BGA via. Fan the vias that connect the BGA pads away from the BGA SMT pads. It is not possible to do this in the middle of the array, but the outermost BGA rows are definately possible. You can also do this on the inner rows for BGA patterns that are hollow in the center. 5. Use thermals for the BGA vias. There is an industry trend to not use thermals for microvias, since they are not pin in hole. This is normally a good thing. However when a BGA goes through the IR oven the vias connected to power and ground can act as a heat sink and cause a possible cold joint. This is not a wave problem, but IR. Process tricks: 1. Use Kapton tape on the wave side vias. This is a pain in the neck to do in volume, but it works. 2. Use a wave fixture to shield the Bottom of the BGA. The goal of all of these tricks is to reduce heat transfer up the via to the BGA ball during wave. My two cents. I have the standard cautionary note that these tricks may not work for your particular design/application and should be investigated before applying. For example there have been industry concerns that plugging vias can later trap flux or other process chemicals. Haven't seen this in my applications however. [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Re: Wave and BGA Author: [log in to unmask] at dell_unix Date: 7/16/97 9:39 AM RE>Wave and BGA 7/16/97 Hi Andre, >From our experience, we found that we have to mask the via array pattern beneath the BGA devices prior to wave soldering. I believe that our assemblers use Kapton tape. There are many solder joint problems if this isn't done. Our vias are also partially covered with mask, but I believe that our vias are slightly closer to the BGA SMT pads. We also went to a high Tg (~180C) FR4 and found a noticeable reduction in via problems on boards that went through this process. Best regards, Greg Bartlett Mercury Computer Systems Chelmsford, MA [log in to unmask] -------------------------------------- Date: 7/16/97 10:37 AM To: Greg Bartlett From: Andre Bisson Hello all, I will like to have comment on any effect that a wave can do on a BGA. We have some boards with BGA on component side and many component on the solder side. Our process will be reflow component side, glue solder side, install all TH parts and go to wave. Is anyone had or have problems with BGA (solder joints problem) after wave? Our via's are half tented with solder masks and the trace connecting the via to the BGA pad is approx. 0.020"-0.030". My concerns are: - Re-reflow of BGA solder ball causing cold solder or any solder defect? - Reliability problems? - Etc. Any advice will be well appreciated. Thank you. Andre Bisson CAE Electronics [log in to unmask] *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To subscribe/unsubscribe send a message <to: [log in to unmask]> * * with <subject: subscribe/unsubscribe> and no text in the body. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************