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January 2000

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Subject:
From:
Michael Fenner <[log in to unmask]>
Reply To:
Michael Fenner <[log in to unmask]>
Date:
Tue, 4 Jan 2000 18:20:58 -0000
Content-Type:
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text/plain (71 lines)
The process Brian alludes to in his last paragraph below was patented 7-8 years ago by a
Japanese company - I think Hitachi, but am not sure now  - they used perfectly flat Au
surfaces and claimed greater reliability than conventional joining methods. The question
really is: are they using it...., but if not why not?


Mike Fenner


----- Original Message -----
From: Brian Ellis <[log in to unmask]>
To: <[log in to unmask]>
Sent: 04 January 2000 08:38
Subject: Re: [TN] Harsh Environments?


Paul

A 0,5 mm space below the 50 mm BGA is easy-peasy, lemon squeezy, given the right
equipment, materials and sufficient time for the process. It's when the space
gets down to less than 0,1 mm that I start worrying,  such as LCCCs with a mass
of flux residues underneath, for them to slowly exude onto the solder joints.

I agree with you that "no-clean" is fine under the right conditions. But I
challenge you to achieve long-term reliability in Anil's exterior climate (or in
Darwin, nearer home for you) with an 800 or so pin-out micro-BGA on an HDIS
circuit with a "no-clean" flux and voltage gradients well into the hundreds of
V/mm. I have had personal experience of portable equipment (semi-professional
digital video camera costing several thousand USD) failing during a one-off
occasion in Indonesia because of the inconsiderate use of "no-clean" flux - and
I was not pleased as I had travelled 200 km from Jakarta especially to film the
event. Apparently, I was not alone, as this manufacturer is now cleaning his
top-end equipment, although he is still using "no-clean" on his consumer
camcorders (which, being smaller, with tighter boards, probably require
cleaning, but that's another story!).

For micro-BGA circuits and similar, I forecast that the days of soldering are
approaching the end, partially because of this and especially because of
lead-free soldering being imposed. I don't think conductive adhesives are the
answer, either, especially anisotropic ones. The crystal ball I have interfaced
into my computer tells me that we are going to see an upsurge of shrinking
insulating epoxies which will pull the BGA into electrical contact and underfill
it, at the same time: a very cheap and reliable method of interconnection with
long-term reliability thrown in, provided the substrate and the component are
perfectly clean at the outset.

Brian

Paul Klasek wrote:

> Agree, Anil definitely speaks from experience, having here one fellow ex
> TATA in Bombay,
> the horror stories (perfect antistatic environment as the condensations runs
> from tables) are real .
>
........

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