In a message dated 05/01/2000 5:40:15 PM Central Daylight Time,
[log in to unmask] writes:
> Fair enough , didn't know SBGA's go so fast through IR,
> but take it from you Phil . Sounds like my memories of "wave" soldering
> over a fry pan. Just kept the flow on safe side .
>
> Joy, no effect on reliability as far as my validations went,
> Earl or Werner (remember the "column flex" constructions stories)
> would know more .
> The support on vibration is more than sufficient,
> and the taller they stand the more reliable they are.
>
> paul
>
> -----Original Message-----
> From: Phil Zarrow [mailto:[log in to unmask]]
> Sent: Monday, 1 May 2000 21:36
> To: [log in to unmask]
> Subject: Re: [TN] I can't X-ray through this BGA!!!
>
>
> Regarding reflow of these "slabs" -
> Don't worry too much about a "shadow" effect. In my experience (including
> going back to Convection/IR reflow of early BGAs, it is a myth that most of
> the reflow is air flowing under the component. If it were, Convection/IR
> would never have worked (and it did/does - just ask Compaq)
Hi Paul & Phil,
Not so much worried about reflow as I am the weight of the part. I have a
buddy that worked at Compaq's Houston plant (before they shut it down) when
they were doing BGA with Vitronic 722's (I/R) so yes Phil, I hear ya'...
Have had some communication with TI (via email) about the issue of not being
able to see through the part with the current xray equipment we have (this is
NOT a slam on the equipment...this TI package only came out in production
within the last 6-months or so...)
TI told me that the part self centers really well, and gave me a generic
profile graphic that I've seen a million times...this is stuff I learned many
moons ago. Most SMT parts will self-center during reflow as long as footprint
geometries are designed right and there's good wetting on all solderable
surfaces. Reading between the lines of their response I took as I didn't need
xray...how else am I to interpret that? Or was it just a response that didn't
want to really get into the real issue?
The one thing that TI didn't address specifically was the weight of the part
and the excessive ball collapse during reflow...Rick Thompson has already
said that he has had a problem with shorting until he found a way to "shim"
these parts. I'm not sure that is something that's a good thing to do
either...no offense Rick, but as you said, it is very labor intensive to do
this, and I can't see on the parts that I have where to put these "shims"
other than in the cavity in the center of the BGA (it's a periphial pattern,
not a full grid) as the balls go out to the edge of the substrate on the
device...which means these "shims" would be forever sealed in the center of
the device to collect all kinds of crap (flux residues, etc.).
Ed Popielarski had a good idea of putting hi-temp solder balls in the
4-corners of the device. These balls would have to be a smaller diameter so
that you would get the collapse that you need for all the other balls, but
would prevent the device from collapsing too far and "smushing" them flat.
Problem I have with that is, why in the %$#@*! should have to jump through
all these hoops to use these parts? Don't ya' think that TI would have
discovered the issue before they released these parts for production?
I know I'm preaching to the choir...just venting I guess....
-Steve Gregory-
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