[Gta04-owner] [Tinkerphones] GTA04A5: good news and bad news

H. Nikolaus Schaller hns at goldelico.com
Tue Feb 28 08:43:51 CET 2017


Hi Marek,

> Am 28.02.2017 um 08:33 schrieb Belisko Marek <marek.belisko at gmail.com>:
> 
> Hi Nikolaus,
> 
> On Mon, Feb 27, 2017 at 7:30 PM, H. Nikolaus Schaller <hns at goldelico.com> wrote:
>> Hi Marek,
>> 
>>> Am 27.02.2017 um 11:46 schrieb Belisko Marek <marek.belisko at gmail.com>:
>>> 
>>> 
>>>> -1.: Only 12 out of 36 (*) GTA04A5 boards we
>>>> have produced, are booting to Linux. The others either have a
>>>> short circuit under the OMAP (which is the general PoP soldering
>>>> problem we already know since the first generations of the
>>>> GTA04) or the OMAP shows no response or does not recognise the
>>>> µSD card for unknown reasons.
>> 
>>> Hmm this is bad. Doesn't something like that happen in first verification run? But maybe I'm wrong.
>>> Did you try to get some info from chip producer what could be a problem or which technology should be used to have it solder properly.
>> 
>> Yes, we asked TI in details some years ago when we built the GTA04A3 and A4.
>> From that we probably know everything what can be known about this DM3730 soldering issue...
>> 
>> And we though that this knowledge is enough to avoid to fall back into the same
>> old problems we had back then when using a new (and modern) production line.
>> 
>> Back then we had to experiment several months to raise yield from ca. 30% to 90%.
>> Then, the production batch was completed. But we had to do a lot of repairs back
>> then as well.
>> 
>> So all this means the production process of the DM3730 + PoP is very very critical
>> to parameters we can't repeat several years later. And therefore we had to start
>> optimization almost from scratch. But do not have the means to continue to reach
>> 90% again.
>> 
>>> 12 from 36 is exactly third which is too high. I'm sorry to hear such bad news.
>> 
>> I am currently making a plan in which sequence we try to repair what (desolder chips
>> and replace). So I am confident that we can come a little closer to 36 of 36.
> This is great news. But AFAIK desoldering/soldering BGA is not really
> easy process

Desoldering is the easier part.

> and sometimes happens that chip is damaged.

Yes, that will happen and we must try a second and third time. At some point
the unsoldering/resoldering stress will have damaged something else.

> Do you have some special idea how to do that? Thanks for sharing.

No special idea except trying...

If we can finally repair 50% of the damaged ones, we are good.

BR,
Nikolaus



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