In a message dated 2/24/99 6:22:34 AM Pacific Standard Time,
[log in to unmask] writes:
<< Hi everyone,
I am having some defluxing problems which I know have been common to the
industry for some time. However, I live in the hope that there may be some
new
thinking on it - namely, the removal of rosin flux from underneath PLCC's. We
use an RMA based flux in our solder paste and, inevitably, flux is trapped
underneath these zero stand off PLCC's. The board design even has a small
square area of solder resist under each PLCC which negates any slight stand
off
we may have had. Our main de-fluxing process using vapour phase HCFC does not
clean underneath and we're left with signs of rosin leaching out in many
areas.
I have already tried an overnight soak in IPA in an attempt to soak it out
however, on baking off the IPA, more rosin bubbles out ! I do have a
semi-aqueous system however I'm hesitant to use this since I don't want to
entrap solvent and/or water under these components and cause myself more
severe
problems. Any comments / suggestions out there ? By the way, due to customer
requirements, I can't go no-clean. Thanks in advance
Bryan Kerr Alenia Marconi Scotland
>>
Hello Bryan!
Zero stand-off PLCC's? Are we talking LCCC's?(A lead-less ceramic chip
carrier) To tell you the truth, I've never seen a PLCC that didn't have at
least *some* stand off. RMA fluxes are pretty mild and you didn't say that
you're having problems soldering, so you have some pretty good solderability.
You're using a solvent to clean it, why not go to a really low residue no-
clean? You can still clean the no-clean residues that are there. It's activity
is going to be less than a RMA, but I think where that'll benefit you, is you
won't have as much residue to clean, and if you do have some residue left
should be pretty minimal, and it'll definately will be less harmfull if there
are any residues remaining than RMA residue would be.
The problem is that there does need to be some sort of mechanical action of
whatever medium you use to get in there and flush things out...the solvent
does break things down, but it still needs to get in those tight places to
flush the junk out. If solvent, water, whatever can't get in there and flush
it out, then likely there'll be some sort of residue remain.
By the way, is your cleaner just a batch vapor defluxer? Is there any sort of
spray, or circulation of the solvent around and over the board? You said that
you were only soaking it in IPA too. If there's not any type of direct spray
or circulation, that could be the whole problem...
It's kinda' like my mom used to chastize me about when I took a bath when I
was little;
Mom: "Steve, do you wash your ears?"
Me: "Yes mom, I did..."
Mom: "Come here youngun', let me check...you did not! You just got em' wet!
You gotta get in there and get that stuff outta there! Lordy, you could grow
potatoes in there!"
(GRIN)
-Steve Gregory-
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