[Gta04-owner] Gta04-owner Digest, Vol 74, Issue 17 using foil whit goldperls

[H. Nikolaus Schaller]

Hi,

> Am 23.02.2017 um 23:49 schrieb joerg at azami.de:
> 
>> Am 23.02.2017 um 12:22 schrieb joerg at azami.de:
>> 
>> Hi all.
>> 
>> About OMAP  unsolderable ?
> 
> Well, it is solderable, but not at expected yield.
> 
>> 
>>> I just wonder if it is possible to use a foil with micro gold pearls an
>>> glue the chip only in stat soldering.
> 
>> Interesting idea! Does that exists at reasonable price or do we have to
> get it
> custom made?
> 
> No Not custom made. I have seen it in a modern chip factory presentation.

I think I have found what you mean:

http://solutions.3m.com/wps/portal/3M/en_US/Electronics_NA/Electronics/Products/Electronics_Product_Catalog/~/3M-Electrically-Conductive-Adhesive-Transfer-Tape-9703?N=8704978+3294001720&rt=rud
http://multimedia.3m.com/mws/media/66235O/3m-electrically-conductive-adhesive-transfer-tape-9703.pdf

It is called "Z-axis Electrically Conductive Adhesive Transfer Tape".

But I am not sure if it is reliable enough. Especially the OMAP3 can get hot (70°C) and cool
down again in suspend so every temperature cycle may weaken the connection until it fails.

Another factor is the conductivity. We have to carry ca. 1 Ampere into the
OMAP at full power... Well, this is spread over ca. 10 or 15 BGA balls.

The data sheet says something which I interpret as <0.3 ohms at 6 mm^2.

Well, we have BGA balls with ca. 0.07 mm^2.

With that, I would expect a resistance of <25 ohms per BGA ball.
This is very likely too much. Not for signals but for power supply.

So we would need such a tape with much lower resistance.

> 
> course there chips hat so many gold plated contacts an thy are so close
> together.
> 
> The Perls were so small not too shorten and so many not to miss one contact.
> So every Contact hat at least one Perl.
> 
> Another advantage is the heat it could resist a higher  one.
> using pressure and heat the robot was very quick on it.
> 
> An I remember they removed the leftover foil after putting the chip down
> and chemically got the Perls for reuse back.
> 
> I'am  trying to remember the footage or search for it again.
> 
> LG Joerg Mueller

BR and thanks,
Nikolaus