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June 2000

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Subject:
From:
Mike Fenner <[log in to unmask]>
Reply To:
Mike Fenner <[log in to unmask]>
Date:
Fri, 16 Jun 2000 10:33:56 +0100
Content-Type:
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text/plain (110 lines)
Few glue suppliers will have info on tensile, but they will have  for shear. Try asking for that
instead or look it up on the data sheet. As a very rough approximation tensile will 85 -90 % of
shear, but be careful when setting up tests that you don't inadvertently test for peel as the
numbers you get will be deceptively low. Some of the adhesive suppliers have a handy torque
tester like device, you set this at say 90% of the theoretical number and this allows you to
test non destructively on real boards.

As Steve said they will be small numbers, [if you assume a typical SMT adhesive has a shear
strength of say 2000 psi you can work out a pretty good estimate of the likely real number from
your dot size.] The shear force on a component from the solder wave is actually quite small and
most adhesives will exceed this. If you are getting drop outs I personally would suggest you
might want to look in to your glue handling procedures. Be on the look out for having two: the
one that's written down and the one that actually goes on. A goodly proportion of adhesive
problems are finger problems/handling related, most probable one is material going out of time


Mike

Original Message -----
From: Stephen R. Gregory <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, June 15, 2000 12:40 AM
Subject: Re: [TN] Pull Test for Glue Process


> In a message dated 06/14/2000 5:48:48 PM Central Daylight Time,
> [log in to unmask] writes:
>
> > Fellow tech netters,
> >
> >                 I am trying to setup some pull test specs for our expoxy
> >  process, we currently using a DEK screen printer and a FUJI FGL2 to
> >  dispense glue. Does any one know what are the pull test (in pounds) for the
> >  different components (example 0805, 1206, Tantalums, etc)?. I have found
> >  that the only way of knowing if a populated board with glue is going to
> >  withstand the handling is by having a pull test as a process measurement.
> >  Any ideas?
> >
> >                 Thanks
> >
> >
> >  Jorge Rodriguez
> >  Process Engineer
> >  Conexant Systems
>
> Hi Jorge!
>
> I'm going to offer my opinions, but they are only that. My opinion of
> quantifying the force it takes to separate a component from the epoxy bond is
> a little over the top, you could be spending your time doing better things...
>
> The epoxy used to bond components for wave solder has very little strength to
> withstand rough handling in the process, and that's where I would concentrate
> my efforts if it were me. People need to understand that the boards that have
> epoxied components on the bottomside need to be handled very carefully. The
> epoxy is only supposed to hold the components on enough to be waved...they
> can't be handled in the same way as boards that have soldered components on
> them. Of course it's not a good idea to be banging on soldered components
> either, but you catch my drift...
>
> I've been through similar situations. The boards come off of wave missing
> bottomside components, and the first thing that has been pointed at was; "you
> didn't cure the epoxy good enough..." or; "you didn't put enough epoxy
> down..." But they have a hard time arguing with me when you can look and see
> that the epoxy that was deposited is still on the board and has the imprint
> of the component is still in the epoxy...it was obvious that the component
> was there and got knocked off...
>
> Epoxy cure is simple...I set 150-degrees C. across all zones in my oven and
> set the belt speed to make sure it sees that temp for at least a minute and a
> half...simple.
>
> When a lot of people hear the word epoxy, they think that it's the same two
> ton strength stuff that you use to repair your broken chair leg with, but
> it's not. People need to learn to handle boards very carefully with epoxied
> bottomside components....
>
> My two cents...
>
> -Steve Gregory-
>
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