There are two (may be more) bga ball attach: screen paste and reflow, or attach a solid solder sphere by laser,or small amount paste, or other method. The paste method got more voids than the solid sphere (I have not see any voids in my past life for the sphere method, either using laser or paste attach- production established method) within balls.
--------------------------
Sent using BlackBerry
----- Original Message -----
From: Inge [mailto:[log in to unmask]]
Sent: Tuesday, April 20, 2010 12:36 PM
To: [log in to unmask] <[log in to unmask]>
Subject: Re: [TN] SAC Shrinkage Voids in BGA Balls
High all.
Are u sure the balls are not shrinked even before soldering? I inspected
hundreds of packages before soldering and found them to be like the neck of
a Galapagos turtle. Both SAC and PbSn look all the same.
I'll send a typical picture to Steve and ask you all: do you have shrinked
balls too before action is taken?
I get question frequently from the operators, because they want see shiny
balls and not old prunes. Myself, I think the wrinkled balls has not
significance.
Inge
--------------------------------------------------
From: "Werner Engelmaier" <[log in to unmask]>
Sent: den 20 April 2010 08:55
To: <[log in to unmask]>
Subject: Re: [TN] SAC Shrinkage Voids in BGA Balls
> Hi Dave,
> A shrinkage void in an ingot occurs where it solidifies last---in its
> center.
> The same is true for SJs, except that they do not necessarily cool from
> the outside in. but a connected to various heatsinks and reservoirs---the
> component is typically a heat sink [coolest] and the PCB is a reservoir
> [hottest], with various heat transfer conditions on the surface due to
> forced air/N2.
> Overall, SJs tend to solidify first at their surface; hence, most
> shrinkage voids are to be found there.
> Werner
>
>
>
>
>
>
>
>
> -----Original Message-----
> From: David D. Hillman <[log in to unmask]>
> To: [log in to unmask]
> Sent: Tue, Apr 20, 2010 10:13 am
> Subject: Re: [TN] SAC Shrinkage Voids in BGA Balls
>
>
> Hi Bev - in theory, a shrinkage void in a solderball is the same physics
> as a shrinkage void in a aluminum or steel casting so no, the shrinkage
> void would not have to necessarily always reach a surface. However, after
> looking at several hundred SAC BGA/CSP cross-sections, I have nearly
> always (99.999%) found a path of a shrinkage void to the solderball
> surface. Because we have a very limited and very small molten solder
> "volume", I think you will find a surface connection. And I guess I'll
> bite - why the question?
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
>
>
> Bev Christian <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 04/20/2010 08:16 AM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> Bev Christian <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
>
> Subject
> [TN] SAC Shrinkage Voids in BGA Balls
>
>
>
>
>
>
> TechNetters,
> Do all SAC shrinkage voids in BGA balls reach/start at the surface of
> the ball? I realize I may be stumped by a 2D cross-section of a 3D
> phenomenon, but I thought I would ask this august body.
> Bev
> RIM
>
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