Whatever and to whomever interested, whohaw is supposed to be wohaw to get
away from the film in which what's her name got naked and starred. Demi?
Anyway, the following is what ended up this way - partly.
Whohaw Guenter,
Your're fine and your messages are all received well. I just never knew you
had to remove the intermetallics, and with a glass brush. That's all I
meant.
I'm the one who's been on holiday. Even though only a few weeks, I must have
missed something during that time. You're helping me see more things than
ever before.
Thanks a million times over. And you know I like stirring the pot. Hell, I
just can't help it.
Please enjoy and thanks again,
MoonMan
----- Original Message -----
From: "Guenter Grossmann" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, October 25, 2001 8:14 AM
Subject: Re: [TN] AW: [TN] Antw: [TN] exposing intermetallic on BGApads...
Hey Moon Man
What bomb? Do you mean my comment about intermetallics? Well, gotta rub my
eyes, I never meant doing something wrong and I even didn't get the irony in
your comment. Seems as if I am still in a holiday mood.
You hoped to see something more from me. Hmmmm. What should I say?
- Every soldering process produces an intermetallic layer
- Intermetallics don't wet to my knowledge and I mean to know that this is
due to the formation of very stable oxides that won't solder either.
If you desolder and remove the remaining solder there is a real chance that
you expose intermetallics. More likely if you remove the solder thoroughly.
I had a case this summer that had nothing to do with rework but with
repeated reflow solder operations. The solder joints didn't look bad, but on
the pads that where not printed dewetting of the HASL could be seen. When we
made microsections we saw that the solder joints had areas where the solder
was touching the IMC but we observed a thin dark line. I wasn't sure
whether I see a preparation artefact or a real thing. However, 2 joints we
looked at had a clear separation between the IMC and the solder some um long
and I believe this was due to exposed intermetallics before the printing
took place. In the dewetted regions no solder was present on the copper only
intermetallics.
Sorry, that I upset you, I didn't mean to but I stand to my point: If you
repair and remove the remaining solder there is a good chance to expose
intermetallics, maybe only partially, and no soldering takes place in the
spots where the IMC was exposed.
Best regards
Guenter
Guenter Grossmann
Swiss Federal Institute for Materials Testing and Research EMPA
Centre for Reliability
8600 Duebendorf
Switzerland
Phone: xx41 1 823 4279
Fax : xx41 1823 4054
mail: [log in to unmask]
Never a bother. Love the joke and say hi to the kids.
Besides the glass brush, my biggest concerns are about fine pitch and BGA
device types and the solder termination area topography they require (flat)
to effect placement, continued alignment, and subsequent reflow and
"acceptable" solder joint formation.
As you know and have observed many times, once device removal is effected,
the solder left is very uneven, to say the least. This, again as you know,
is why we wick off the solder left after the removal process.
This, then, is the dilemma as I see it. In your terms, we now expose an IMC
layer, to whatever extent, preventing solder "wetting" in some areas. I
guess, this is a random occurrence (where and how much IMC) is left.
Therefore, doesn't this point to sh luck to again effect "acceptable solder
joints?
Enjoy your kiddy romp,
Earl
----- Original Message -----
From: "Guenter Grossmann" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, October 25, 2001 8:37 AM
Subject: Rework
Sorry for bothering you again but I just had a thought:
1) Someone doing a job thoroughly an clean does his / her job good
2) Doing a job only partially is bad workmanship
3) Thoroughly removing solder exposes IMC and produces bad solder joints
4) Partially removing the remaining solder protects the IMC and leads to
acceptable solder joints according to MIL and ESA standards
ERGO: MIL and ESA standards support bad workmanship
( just a joke that came to my mind before I go of to play with my kids)
Have a great day
Guenter
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