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Paste / Flux during rework?

Sam_B

#21088

Paste / Flux during rework? | 9 August, 2002

Just started doing BGA rework. After the removal of the "old" component and after site cleaning/component reballing I am ready to install the component on the PCB. It is recommended to apply flux or paste to the board/component. I would appreciate more information on why paste is used over flux and vise versa. What are the advanteages of one over the other? Is it correct to consider that BGA rework follows the same principles as hand rework/soldering and simulation of reflow oven environment. Also, is it better to apply paste/flux to the PCB or the component? thanks sam

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RDR

#21108

Paste / Flux during rework? | 12 August, 2002

I use Paste for high temp balls and/or co-planarity/warpage issues. normally I only use paste flux for ball attachment. One down side to paste application is registration and volume anomalies with those little micro-stencils (for me anyway).

Your rework profile should match the original reflow profile as best you can.

I usually apply flux to only the PCB but adding it to the balls probably wouldn't hurt anything unless you end up with too much flux. (I have had balls "blown out" from an excessive amount of flux being applied, I do not know if it was the flux type or a bad lot that caused this but when we reduced the amount the problem went away?!)

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#21109

Paste / Flux during rework? | 12 August, 2002

What I've done w/ eutectic ball BGA devices is after removing the BGA from the PCB, solder-suck the lands- get em nice a flat, apply a thin coat of gel flux to the solder lands and then a thin coat to only the bottom of the solder balls on the new BGA. Place and reflow as normal. I had excellent results. The BGA was 352 I/O w/ 1.27mm ball pitch.

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