Re-heating BGA Chips

[kf4rca]

What techniques has anyone had in re-heating BGA chips to working condition?
I read somewhere someone used a halogen puck light with success. I would imagine the ROHS boards might need something more drastic. Thanks.

[JohnCT]

Originally Posted by kf4rca

What techniques has anyone had in re-heating BGA chips to working condition?
I read somewhere someone used a halogen puck light with success. I would imagine the ROHS boards might need something more drastic. Thanks.

To do it right, a BGA reworks station is the way to go. Heats the bottom with IR while using hot air on the top.

Still reheating BGAs is risky. They're designed to be ramped up to solder flow one time really, and without a really expensive automatic setup that monitors temp over time, it's more so.

I built a box with a small IR heater in the base, and watch the temp of the board with a temp gun. When it gets to about 100C, I start the reflow at the top with the hot air, air vol at high speed. Usually ramp up from 150C start to about 325C over a two minute window, then shut off the air and the IR bottom heater and let it cool down naturally.

EDIT: if you want to screw around cheaply, a hot air gun delivers a lot of heat and air for a lot less money. I actually use one sometimes, particularly if the BGA is really big. Get some junk circuits and practice on those. A heat gun can actually blister a board if you're not careful. Trial and error.



John

[kf4rca]

Thanks. I'll give that a try. This BGA has an aluminum heat sink. Should I take it off first?

[JohnCT]

Originally Posted by kf4rca

Thanks. I'll give that a try. This BGA has an aluminum heat sink. Should I take it off first?

Yes, if it seems like it can be taken off without a lot of force. Heat up the heat sink first and see if it will come off without too much effort. You most certainly do not want to put too much pressure on the BGA and damage the foils beneath it.

If it seems like it's bonded too tightly, go ahead and reflow as is. The aluminum sink should transfer the heat pretty well.

BTW, if the BGA is a metal one (like a Broadcom), my understanding is that the *inside* of the BGA needs the reflow, not the bottom where it meets the circuit board. Supposedly, these ICs have two dies that are solder balled together, and these will fail internally. For these, less heat is actually required because inside of the chip will reach reflow faster than the bottom of the chip at the board will.

John