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Stencil for BGA re-balling

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Stencil for BGA re-balling | 7 November, 2008

What should be stencil size to reball the BGA of 0.6MM ball dia.

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Stencil for BGA re-balling | 11 November, 2008

By the way you asked the question, we assume that by "reballing" you mean bumping, we should be able to figure that out: * Volume of the ball = ( pi*d^�)/6 = [355/113] *0.6*0.6*0.6]/6 = 0.11mm^3 * Volume of solder required = 2*volume of ball = 2*0.11mm^3 = 0.22mm^3 * Volume of cylinder = pi*[d^2]*t/4 = [355/113]*[d^2] * t/ 4 = 0.22mm^3 * Diameter of aperture = [[0.22mm^3]*4*[113/355]/t]^[1/2] = [[0.28]/t]^[1/2] * Assuming the pitch of your part is 1.0mm and the web is 0.08mm, the diameter of aperture = 0.42mm * Stencil thickness = t = 0.28/[0.42mm]^2 = 1.6mm * Area Ratio = d/4t = 0.42mm/[4*1.6mm] = 0.07 [Ow!!! SB GT 0.66. Not good, but you get the idea. You can figure it out from here. Obviously, a 0.42mm square would help some.]

Now, here are the caveats: * We're not good at math, but that doesn't stop us from trying. So, we don't guarantee the math is performed correctly. So, check it yourself.

Alternatives are: * BGA Reballing Preforms from SolderQuik [] Winslow Automation says it's fast, easy, and cost effective * Photo Stencil offers a universal BGA repair tool []. The tool holds the BGA package in place with a ball stencil registered to the holding tool. The entire tool, with balls in place, is sent through the reflow oven. * SMT Sales Associates [] sells a fixture for reballing BGA one at a time. You apply liquid flux to the bottom of the part. Place the part in the fixture. Pour the spheres into the fixture and reflow the part. You would need a fixture for each part number you want to reball. The kit contains the fixture, 25K spheres and the liquid flux. The kit sells for $300. * Finetech Ball Array Placement Module [,0/Rework_Modules___Tools/BGA_Reballing_9s.html] can handle simultaneous, high precision placement of up to 200 solder balls directly onto a substrate or wafer.

On the other hand, if you're just looking to print some solder paste that will attach a reballed BGA, we'd suggest 17thou (0.43mm) apertures on 5 mil (0.125mm) foils. [Again assuming that you're talking about a 1.0mm pitch BGA.]

Now, if the BGA is already reballed, we'd just dunk it in some flux, we don't need no stinking paste, and solder the stuff out of it. Say, 'good night' and go drinking.

For future reference, oftimes, giving us the pad size and pitch are more useful information that ball diameter.

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