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BGA chip corner epoxy / adhesive?

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SMTrework

#46037

BGA chip corner epoxy / adhesive? | 6 December, 2006

Hello, we rework BGA packages that come back from the field. I've seen on occasion a black and or red "epoxy" substance from the manufacturer on the corner of some board's BGA chips that I imagine are applied to increase corner bond of the chip to the PCB.

My question is what is this stuff called? Is it the same as BGA "underfill"? Does any one know where I can buy it from?

Thank you.

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#46038

BGA chip corner epoxy / adhesive? | 6 December, 2006

Questions are: * When you say, "corner of some board's BGA chips", is it on the top of the package or between the board and the bottom of the package? * If between the board and the bottom of the package, does it span the distance between the board and the bottom of the package? * If between the board and the bottom of the package, how many corners? * How do you characterize [eg, big, small, heat slug, etc] the BGA that see this glue?

Without answers, ideas on the purpose are to retard: * Excessive ball collapse in BIG-ass, heavy heat sink BGA-types. * Excessive flex of BGA during reflow. * Differences in flex between BGA and main board to limit corner ball cracking in finished product.

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SMTrework

#46039

BGA chip corner epoxy / adhesive? | 6 December, 2006

Hi Dave,

This is manufacturer applied epoxy / adhesive to minimize package "lifing" from chassis flexing and thius board flexing.

I have seen the complete array area covered with this black or red epoxy in some cases (i.e. the underfill that I've read about) but what I'm mainly after is info about the epoxy that is used only in each one of the four corners between the bottom of the chip and the PCB.

Once again, I would imagine this is applied to eliminate the "lifting" of the corner due to flexing during usage of the device due to heat, shock.. ect..

Thanks again.

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Guest

#46044

BGA chip corner epoxy / adhesive? | 7 December, 2006

Materials you see are corner bond adhesive, main purpose of this is mechanical shock absorber , it promotes additional adhession to lessen stress to solder joints incase device subjected to mechanical stress like dropping.By function, corner bond is also one way of undefilling, other approach is underfilling the whole BGA or CSP area.

When I was in the assembly I used UF material from Emerson and Cuming, you may want to look at their website, I believe they even have the reworkable underfill.

Hope this would help .

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#46054

BGA chip corner epoxy / adhesive? | 7 December, 2006

It may be for a double sided reflow process. Yes, some people do put the BGA on first. I know this first hand.

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RDR

#46060

BGA chip corner epoxy / adhesive? | 7 December, 2006

I would bet that it is a SMT adhesive used to ensure that the BGA does not move during a secoindary reflow prcess. this glue is easily removed with a soldering iron.

Russ

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#46074

BGA chip corner epoxy / adhesive? | 7 December, 2006

We agree with "guest" above. This a "chip bonder" type material used to improve the reliability of array type devices.

"A relative comparison of the N50 values is given below: No underfill = 1.0X (baseline) Corner bond = 1.3X Non reworkable underfill = 1.4X Reworkable underfill = 1.7X

The above data show that an increase in median fatigue life of 30-70% is observed with the use of an underfill, under accelerated testing conditions. The exact amount of life enhancement achieved will clearly depend on the actual operating conditions. It is to be noted that underfill encapsulation may not be required solely for fatigue life improvement, if the field application conditions do not warrant it. However, when the module is subject to high compressive loads, the underfill solution provides both creep mitigation and enhancement of thermo-mechanical fatigue reliability." [Development of BGA Solution for the IBM PowerPC 970 Module in Apple's Power Mac G5; ECTC 2004; Edwards, IBM & Chambers, H Apple Computer etal]

N50: Cycles to 50 percent failure

Try: Loctite 3509 * Cure time(min): 40 * Cure temperature: 150*C

We have no relationship, nor receive benefit from the company referenced above.

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