What a relief : todlers in US of A do not have to wrap up themselves in
kevlar49 composite blankets to dodge bullets from nearby kindergartens as i
mistakenly assumed reading of "security" blankets .
Thanks Werner, you've had me worried for a moment.
Inge, is all correspondence on this polymer versus paste going private = did
you get any response at all ?
Left it one day as to obstain from perceptions of being one of oldies (not
enough for granies):
not a wisper on the subject !
Risk indeed , you know this silver polymer versus solder paste is too hard
to resist .
I'd say yo' are much more unique than 5%, i'd be pretty certain no more than
1% uses conductive polymers for joints.
Less than 15-17 answers would validate my theory .
Some 5 years back when i started auto dispensing i was going to go full way
;
that is dispense and glue all , but all of the trial runs on strenght and
life dismuly failed :
>comparing to solder< . Did few more couple years later , than gave up .
Even when we runned ipc-sm-275 cycling for some 7 months on solder,
most of the failures/false alarms/problems were the silver epoxy event
detector attachments dropping off,
drove me around the bend ,
solved eventually by skipping the original reco of silver gluing AFTER the
assembly;
and did a thin tinned wire wrap with a couple of turns around the worst
offenders going through reflow at the same time,
with some 1" tail for event detector attachment after without thermal impair
to joint.
Did go through them all (polymers), still have a file foot thick : nothing
compared to solder,
with few caps cracking i could justify it in some instances , not as an
overall process .
A relatively few negatives with solder tensions on caps as I remember
Werner's quoting few european studies :
can be addressed by different pad geometries , height of fillets, etc. in a
quite practical ways,
so from civil perspective here it's thumbs up to solders of any kind .
Been actually often thinking ; why Inge ploughs through this hard way ;
but than; noo, he knows, must know what he does .
Did you notice i never actually asked WHY ?, despite being extremely curious
?
Now, since yo opened the topic (notice i did NOT change the mail heading);
lets discuss this under cover of voids :
With this leadfree market manipulations ;
what practical applications would you (say on gold metalisation) see as
comparable to solders ?
That is, would we see a step up from leaded alloys to conductive polymers ?
And in short term , considering your long battle with flakes,
what's the application (thermal sensitive?)you have on hands?
Did you address the resistivity changes ?
-----Original Message-----
From: Ingemar Hernefjord (EMW)
[mailto:[log in to unmask]]
Sent: Tuesday, 21 March 2000 19:34
To: [log in to unmask]
Subject: Re: [TN] Voids in BGA Balls after reflow
Yes, Bob,
well recognized. We were stunned by solder balls looking like rotten teeth
after the soldering/cleaning process. Typical was that all the "caries"
holes were on one and the same side of all balls. Explanation: a)the balls
consisted of two zones with different grain phases, caused by the BGA
maker's production method. b)we used a flux cleaner that dissolved poor
grain bindings in this two-zone interface and the result looked like what
happens when a mouse takes a bite in the cheese. Well, there is a whole
report about it and MOTA changed the ball concept, since then I have heard
of no more such problems. If you want some pictures for comparison, I can
send to you, Bob.
It's strange that we still get some soldering problems after decades of
knowledge about the processes. One reason may be this: old 'goodies'
disappear, newcomers more interested in IT and stockholding affairs. I knew
such an ol' goodie at a company, a metalurgical dr from Germany, he WAS
soldering personified (devotion and deepest interest), but when he retired
noone took over, the lab personel was spread and the new bosses spent no
more money. Many new in the game just scrap the surface of the mystery of
soldering. Luckily, we have TWI, IM and other institutions nearby, in US
there is China Lake, Sandia, Rome, IBM and....and Klein Wassink's soldering
bible...oceans of knowhow for those who like digging after treasures.
I take the opportunity to ask about silver adhesive vs. soldering. Just
wonder how many percents of the worlds component mounting is done with
adhesives instead of solders. The adhesive makers claim that their products
fit well for most applications, but many, many hesitate to change from
solder to 'glue'. I don't ask for a storm of pros and againsts...not at all,
just a qualified guessing from someone: how many percents? What do you
think? 5%?
There is a risk that some oldies will talk, how do we stop them? (He-he)
Ingemar Hernefjord
Ericsson Microwave Systems
-----Original Message-----
From: Bob Perkins [mailto:[log in to unmask]]
Sent: den 20 mars 2000 22:01
To: [log in to unmask]
Subject: [TN] Voids in BGA Balls after reflow
Hello Technetters
Recently with the help of a high end piece of x-ray equipment we
have noticed voids in the spheres of the bga after reflow, "see
attachment-file". Has anyone seen this before, or has any idea how the
voids are created? Also does anyone know if this is a bad or good thing?
Does anyone have any recommendations to the profile?
Thanks
Bob Perkins
Automation Technician/Manufacturing Engineer
Aimtronics
[log in to unmask]
<<wboard6.jpg>>
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