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Soldering BGAs

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dknguyen

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Does anyone have experience about what is requied to reflow a BGA?

I ask because lately there are adhesive stencils that permamently adhere to the PCB and then you squeegee the solder paste onto the stencil and place the BGA onto the stencil. THe thickness of the stencil apparenly makes it so you can feel where the BGA balls fall into the holes on the stencil for proper alignment. But BGAs apparently self-center during reflow anyways so I'm not sure if this would help with doing a toaster oven reflow at home.

Like with a $50+ chip like an FPGA it might be unacceptable and you should just pay to get it professionally mounted. But I know of no local places. But maybe for a $20 MCU that is a 256BGA it might be acceptable if you mess the chip up and need to use another one? It'd be hard to check though if it's actually soldered in properly.

Why you ask? it'd be mighty nice to have the LCD conntroller that is only available on the 256BGA packages. Anything smaller would require me to bit blast stuff...it's doable though with the M0 coprocessor and the SGPIO on the LPC43xx.
 
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Does anyone have experience about what is requied to reflow a BGA?
We had a very expensive BGA rework station (Weller WQB3000) at my last place of employment.
There are all sorts of problems with this, even if you have all the right equipment.
We all had a go at this, and even the sales rep for the equipment had real difficulty during a sales demo making it work.

First you need to fit the new chip to a jig that aligns it perfectly with the BGA pattern on the circuit board. This alignment is usually done with a small CCTV camera mounted to the jig.

Then you preheat both board and chip with a combination of infrared radiation and hot air from above and below.
The chip is then lowered onto the board, and as you say, surface tension in the molten solder "pulls" the chip into final position.

The first problem is heating the board. Too much heat for too long can delaminate a multilayer PCB, cause it to bulge and buckle under the BGA, and totally destroy the board. Too little heat and the process will not work, or work imperfectly.

The chip needs to be lowered onto the board dead square and dead on alignment. You only get one go, and it must be done fairly quickly because overheating will definitely destroy things.

Let a professional replace any BGA chips for you, and even then, don't be too surprised if your board never works ever again.....
It is a very hairy procedure at best, although someone doing it all day, every single day will get pretty good at it.

There is a vast difference in setting up a fully automated repetitive surface mount manufacturing process, to doing a one off repair job.
The automated process, you can afford to waste ten boards getting the times, positioning, and temperature profiles exactly right for that specific BGA chip size.
The automated machine then can do it a million more times with perfect success every single time.
A one off repair with one odd sized BGA chip is a whole different ball game, even with the very best equipment..
 
I have never had consistant luck with the self centering thing and with a BGA there is no easy way to tell. Could be I need to develop the touch for how and where to tap the PCB.

The stencil sounds good to me. Do you have a link ?
 
Its called QuickStencil. You can nget it from different places like stencilunlimited or solder.net. Google QuickStencil. QuickStencil solves the centering. I'm asking about what can go wrong with the heating.
 
We had a very expensive BGA rework station (Weller WQB3000) at my last place of employment.
There are all sorts of problems with this, even if you have all the right equipment.
We all had a go at this, and even the sales rep for the equipment had real difficulty during a sales demo making it work.

First you need to fit the new chip to a jig that aligns it perfectly with the BGA pattern on the circuit board. This alignment is usually done with a small CCTV camera mounted to the jig.

Then you preheat both board and chip with a combination of infrared radiation and hot air from above and below.
The chip is then lowered onto the board, and as you say, surface tension in the molten solder "pulls" the chip into final position.

The first problem is heating the board. Too much heat for too long can delaminate a multilayer PCB, cause it to bulge and buckle under the BGA, and totally destroy the board. Too little heat and the process will not work, or work imperfectly.

The chip needs to be lowered onto the board dead square and dead on alignment. You only get one go, and it must be done fairly quickly because overheating will definitely destroy things.

Let a professional replace any BGA chips for you, and even then, don't be too surprised if your board never works ever again.....
It is a very hairy procedure at best, although someone doing it all day, every single day will get pretty good at it.

There is a vast difference in setting up a fully automated repetitive surface mount manufacturing process, to doing a one off repair job.
The automated process, you can afford to waste ten boards getting the times, positioning, and temperature profiles exactly right for that specific BGA chip size.
The automated machine then can do it a million more times with perfect success every single time.
A one off repair with one odd sized BGA chip is a whole different ball game, even with the very best equipment..

Honestlyy, I would send away for it. But when there are no local places and they are either in another country or across the country, it means you have to send both the chip and PCB and then get it back paying for everything along the way.

This is for a hobbyist project so it's one-off. I wouldn't try using hot air just because hot air equipment is super expensive and prone to fail and you still need to get a board preheater. I'd be using a toaster oven. The centering and possible bridging between balls and solder paste has always been a biznatch that I never considered trying it. But with the quickstencil to provide a "socket" for tactil centering and a 3D divider between solder balls, I was curious about to your opinion as how much the chances of sucess would increase by. I've heard that you don't even need solder paste just lots of flux because the solder balls are enough?
 
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Fair enough.
My experience with BGA is pretty limited except for attempting to use the Weller BGA repair station.
Success with that was probably less than 50% and all five of us tried repeatedly.
Some expensive irreplaceable customer boards were effectively trashed forever in the process.

Not trying to discourage anyone from having a go. Gaining some skills can be a long painful process of trial, error, and learning.

But at least practice first on some old trashed circuit boards with some of the smaller BGA chips before attacking anything important.
 
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