[Gta04-owner] GTA04 production

[Dr. H. Nikolaus Schaller]

Hi Glenn,

Am 25.07.2012 um 11:50 schrieb Glenn:

> On 25/07/12 11.14, Dr. H. Nikolaus Schaller wrote:
>> Just a short note: we are coming close to a full understanding
>> of the issues.
>> 
>> We have now three independent 3rd-party hints that the DM3730CBP
>> BGA chip might get warpage during soldering. Not the same for
>> all chips but only some. So using a standard BGA soldering process
>> that works perfectly for many other BGAs may randomly fail with these
>> short circuits, giving a very suboptimal yield, wasting a lot of money...
>> 
>> This warpage appears to depend on the reflow temperature profile
>> and atmosphere. I.e. it is quite tricky and experimental to get close to
>> 100% yield.
>> 
>> But if you eventually know what the root cause is, it is easier
>> to develop a really good solution.
>> 
>> So I am now confident that we will master this soon.
>> 
>> Nikolaus
>> 
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>>   
> 
> 
> Jubii ;-)
> 
> -
> 
> Is it possible to test the warpage during a pre-heating PCB-less step in a nitrogen-atmosphere to disclose chip-packages - especially if they warp more than TI specifications?


You mean trying to filter out those chips who *will* warp more than others? I am not sure that this works.

And the spec in the data sheet says something about 0.1mm warpage. With BGA balls
diameter 0.2-0.3mm. I.e. 30-50% pressure on a ball is *within* spec. I think we can't return
them especially if others have improved their soldering process so that it works.

So there are generally two levers:
* reduce warpage by different temperature profile and atmosphere (here we have a special contradicting requirement in our design: because the board is so small and the UMTS module has so much shield the heat must be more than usual or the UMTS module is not soldered properly. But this increases warpage of the CPU.)
* accept warpage, but reduce its effect (balls getting squeezed and risking short circuits). That appears to mean to make the holes in the middle of the stencil smaller so that less solder paste is being printed

Nikolaus