Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Land Grid Array soldering

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#75537

Land Grid Array soldering | 13 April, 2016

I am working on soldering an Large LGA module to a PCB and am having some issues with opens due to variation in the board flatness. I have tried adding more paste but get shorts and excess flux as I get above a 7 mil stencil. I have tried adding solder balls to the module with good results. The problem there is that it is capital intensive and requires changes to my testers. Moving back to a solder paste solution I was wondering if anyone has used a larger partial size paste. Does anyone make a type 1 or 2 paste for electronics applications?

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#75543

Land Grid Array soldering | 14 April, 2016

Why don't you fix the PCB flatness instead? If that is not the problem, I will check the part warping during the reflow process.If the part is large as you mentioned, it probably warps a lot during reflow. Try to bake the parts in front,based on MSL level datasheet.

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#75544

Land Grid Array soldering | 14 April, 2016

You can also try different paste from what you are using(may be paste with lower melting point).

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#75546

Land Grid Array soldering | 14 April, 2016

I doubt that your problem is driven primarily by irregularities in your circuit board. My bet is that you’re seeing defects caused primarily by the warpage in your LGA.

Consider using advice often given for minimizing warpage caused defects in BGA soldering as your guideline. For instance: * Try to minimize warp by slowing down the heating and cooling periods on your reflow soldering recipe * Use a solder paste tailored to resolve head-in pillow, BGA warping and the like * Implement a proper MSD program. Assess the effectiveness of your current MSD procedures by processing a freshly baked LGA and comparing that to a LGA processed routinely * Modify your stencil design according to the issue. For instance: ** For opens near the corners: increase aperture volume or over-print in that area ** For shorts near the heat spreader, reduce aperture volume in that area

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#75576

Land Grid Array soldering | 21 April, 2016

> I have tried adding more paste but get shorts and excess flux as I get above a 7 mil stencil.

You do need the thicker stencil.

To prevent the shorts, you need to have your pick-and-place machine probe the exact height of the board (at multiple locations to account for warpage) and release the LGA after it contacts the paste but before it has deformed the deposits.

Not all pick-and-place machines can do this. You might need to buy one that can.

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#75586

Land Grid Array soldering | 25 April, 2016

Hi Adamjs! Flux or paste is controlled at a depth of 50-60% per cent of the ball diameter prior to placement of a BGA or to place a PoP component on to a board or other device.

For more details visit us at Soldertools.net

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