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Very Low Volume BGA Assembly

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John S.

#41722

Very Low Volume BGA Assembly | 23 May, 2006

Can anyone provide advise on implementing assembly of a very low volume BGA based board (less than 1500 units/year)? We do not currently do any BGA assembly and lack the inspection/rework equipment thats associated with these parts. Thanks John S.

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#41726

Very Low Volume BGA Assembly | 23 May, 2006

Make sure your reflow profiles are the best you can make them.

You will probably want to, at the very least, get some sample BGA's and boards to sacrifice to profiling. Drill a small hole through the board into a middle ball of the BGA. Also put a thermocouple outside the BGA so you can get an idea of the delta T.

I have seen a little diamond shaped mirror that was great for looking under the BGA's.

Unfortuneately I can't remember the make. With it, a microscope, and a good inspector it was almost as good as an Ersa scope.

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TMC

#41727

Very Low Volume BGA Assembly | 23 May, 2006

Do you have an automated line with pick and place equipment that can handle your BGA's?

Inspecting the board is a must after profile development. You may send the 1st board to a CEM for X-ray inspection. If you have a consistent process (printing, pick and place, reflow) subsequent inspections are not required.

A BGA rework station is used for well, rework. You may even use it as a placement system for high pin/ball count I/C's.

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#41728

Very Low Volume BGA Assembly | 23 May, 2006

I would take a BGA over a fine pitch QFP any day of the week. Unless it is a BGA with a high ball count, place them by the body if you don't have upward looking vision. Make sure your reflow process is good and the parts are placed in the correct orientation. If you do it correct, you don't need any fancy inspection equipment or reqork equipment. Have been placing BGAs for many years without rework equipment or special inspection equipment. Have also hand placed 0.031" pitch BGAs by hand without any trouble.

Oh I should backtrack and mention that this is with lead paste. Lead free might present some additional trouble if you hand place the BGAs.

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Chunks

#41729

Very Low Volume BGA Assembly | 23 May, 2006

Chris is right. You can do a good visual after placement if you have outline marks on your silk screen. That helps a lot. What size BGAs are you talking about. That would determine how critical you want to get with inspection.

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#41739

Very Low Volume BGA Assembly | 23 May, 2006

We've been placing BGAs for a while now, and I personally had to x-ray every one of them. The only time we had a placement problem was when a few parts were placed by machine in the wrong orientation. The operators fixed it by hand before it went through the oven, but this led to bridging on the middle balls that we probably wouldn't have seen without x-ray.

We don't have out own x-ray; we rent a local university's machine for $50/hour. Not the most convienent arrangement, but you can't beat the price at our volumes.

Rework seems like it could be a problem. We have an Metcal APR-5000 for BGA rework, and we have had to use it. Without your own equipment, it seems like you would either have to scrap boards with bad BGAs, or pay someone else to fix it for you.

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#41740

Very Low Volume BGA Assembly | 23 May, 2006

Another major consideration is moisture. I saw a batch of BGA's delaminate.

With the X-ray it looked like the balls were shorted. (Well they were but I mean that wasn't why the BGAs had failed.)

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#41741

Very Low Volume BGA Assembly | 23 May, 2006

I was trying to hide my shame on that one, but we have seen failures that we attributed to moisture issues as well. There was nothing to see with the x-ray, but the BGAs didn't work. Replaced the parts with some that had been properly stored/baked out and the problem went away. Fortunately, the cost of the parts didn't warrant a more thorough investigation, but this could get very expensive if you're not careful.

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#41742

Very Low Volume BGA Assembly | 23 May, 2006

Hi,

Ok I have some numbers for you on my process. For the last 2 years we have been placing 4 BGA on a 2" X 5" X 0.062" PCB. The BGAs are 16X16 256 ball, 15X11 165 ball, 8X8 64 ball, and 26X26 456 ball. The 8X8 is 0.8mm pitch and the others are 1mm pitch. We used to place these by the body until we got a new machine. We had no trouble with the old machine just needed more feeder capacity. There has been only one time when we had to rework the 26X26 ball BGA and that was a rotation problem. We scrapped the 25 units actually. We have seen little to no BGA scrap and we run 5000 units per year.

I have worked for two other much larger companies in the 90s and we placed BGAs by the body. We even had a nice Air Vac BGA rework station. Never had to use it for BGA rework. We did not have an Xray machine and we used IR ovens back then. We used Dek 265s and Fuji IPs.

It is my opinion that you do not need Xray or BGA rework equipment and you can still build a high quality product that uses BGA technology. Yes, when you run into trouble, the Xray and rework equipment is nice to have. I can also say that 1 mm pitch 456 ball BGA gives us less trouble than a 0.5mm pitch QFP with less I/O count. Again the catch is you can't easily see a failure with a BGA.

That's my 2 cents,

Chris

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