Ingemar, my friend,
We are in agreement on voids—I always said, that because they are easy to see with a very expensive machine [X-Rays], people think they MUST have some significance.
On SHINY—we are our own worst enemies; for years we beat into our operators 'YOU MUST HAVE SHINY JOINTS'—why, because with good eutectic SnPb they were easy to get, and signified 'GOODNESS.' How many solder joints have been reworked for cosmetic reasons, and perhaps making things worse?
With SAC you do not get SHINY. Indium, Alpha, and Kester spent a fortune coming up with alloy additions to give SHINY SJs, with some success but at the cost of other properties, mostly higher Liquidus.
Do not know what the Xilinix alloy is, so I cannot even make a half-a...SORRY, meant -intelligent, comment.
Skoal—its 17:00 here and 23:00 at your end—time for a drink,
Werner
-----Original Message-----
From: Inge <[log in to unmask]>
To: Werner Engelmaier <[log in to unmask]>; [log in to unmask]
Sent: Tue, Apr 20, 2010 3:14 pm
Subject: Re: [TN] SAC Shrinkage Voids in BGA Balls
Allright Master E,
but let's put it this way: I'm not afraid of voids (except for voids in my memory) but I'm speaking shinyness. A whole generation of operators have been brainwashed to demand absolutely mirrorlike and shiny solder joints without a wrinkle, and despite my higher level of technical knowhow, I have problems to convince the guys, that wrinkled balls after soldering is nothing of abnormal. We do see BGA balls with wrinkles before soldering as well as after soldering, they are untouched. The printed solder paste wets good enough up a little bit, but the rest of the balls have not undergone any shifting, wrinkled before, wrinkled they stay. That's what I ask you: do you have the same experience, anyone of you? Have a look at the picture at Steve's site. These are typical for Xilinx balls, and they have had this exteriour for more than 10 years. I asked Xilinx about it, and they said that such are the balls they buy from one and the same supplier of theirs.
/Inge
--------------------------------------------------
From: "Werner Engelmaier" <[log in to unmask]>
Sent: den 20 April 2010 09:59
To: <[log in to unmask]>
Subject: Re: [TN] SAC Shrinkage Voids in BGA Balls
> Agreed.
>
>
>
>
>
>
>
>
> -----Original Message-----
> From: David D. Hillman <[log in to unmask]>
> To: [log in to unmask]
> Sent: Tue, Apr 20, 2010 12:06 pm
> Subject: Re: [TN] SAC Shrinkage Voids in BGA Balls
>
>
> Hi Werner - we are both on the same page (I should have typed out a more
> detailed response). As you detailed, the actual metallurgical reactions of
> shrinkage are the same, the focus should be on what is staying molten
> last. We have observed on some BGA solderballs that were part of the
> circuit connection to ground planes some slightly different shrinkage void
> differences due to the solidification reactions. Interesting from a
> technical viewpoint but didn't make a difference from a solder joint
> integrity perspective.
>
> Dave
>
>
>
> Werner Engelmaier <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 04/20/2010 10:55 AM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> Werner Engelmaier <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
>
> 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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