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September 2003

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Subject:
From:
"Dehoyos, Ramon" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 11 Sep 2003 13:13:25 -0700
Content-Type:
text/plain
Parts/Attachments:
text/plain (165 lines)
                Peter:
>    You must have a bad batch of glue or a bad bottle.  Normally glue lasts
> several days after the bottle is open. You should send a sample of the
> glue to the manufacturer to be analyzed.  The liquid you see may not be
> water, but the solution the glue is in.  It may be easier to repeat the
> process with known good glue, even if it has to be done manualy.
                Regards,
                Ramon



> Hi Technet,
>
> I didn't receive many responses when I asked if anyone has come across
> seeing the moisture-within-the-glue defect underneath SMT components.
>
> In order to remove the mositure off the assembled units, I am
> experimenting
> with various low temp. baking cycles. I like to ask if anyone have
> experience removing moisture that was trapped within the glue underneath
> SMT components (0805s)?
>
> Due to other thermal sensitive T/H components on the boards I am limited
> to
> 100C baking or less.
>
> Rgds,
> Peter
>
>
>
> Date:         Thu, 28 Aug 2003 13:29:00 -0400
> Reply-To:     [log in to unmask]
> Sender:       TechNet <[log in to unmask]>
> From:         joyce <[log in to unmask]>
> Organization: EXFO-TO
> Subject:      Re: Moisture under chip capacitors
> X-To:         "TechNet E-Mail Forum." <[log in to unmask]>,
>              "Peter L." <[log in to unmask]>
> In-Reply-To:  <[log in to unmask]>
> Content-Type: text/plain; charset="iso-8859-1"
>
> It is epoxy based material.  If you see voids, it got be there before
> curing....
>                                                jk
>
> >-----Original Message-----
> >From: TechNet [mailto:[log in to unmask]] On Behalf Of Peter L.
> >Sent: Thursday, August 28, 2003 12:26 PM
> >To: [log in to unmask]
> >Subject: Re: [TN] Moisture under chip capacitors
> >
> >
> >The adhesive was printed and cured at no more than 2deg/s and
> >150degC for 100secs.
> >
> >The particular adhesive used was Epibond 7275. We suspected
> >that it was a material related issue - either the glue was
> >mishandled and left too long on the line, or old/ expired
> >batch of glue was used.
> >
> >Any suggestion on method to drive the moisture away under the
> >components? Baking conditions?
> >
> >
> >Rgds,
> >Peter
> >
> >
> >
> >
> >>Date:         Mon, 25 Aug 2003 07:47:30 -0400
> >>Reply-To:     [log in to unmask]
> >>Sender:       TechNet <[log in to unmask]>
> >>From:         joyce <[log in to unmask]>
> >>Organization: EXFO-TO
> >>Subject:      Re: Moisture under chip capacitors
> >>X-To:         "TechNet E-Mail Forum." <[log in to unmask]>,
> >              Peter Lee <[log in to unmask]>
> >>In-Reply-To:  <000001c36abe$e03472d0$7e63ad8e@homeg8br34o791>
> >>Content-Type: text/plain; charset="iso-8859-1"
> >
> >>What is the adhesive and how was it cured?
> >                                            jk
> >
> >>-----Original Message-----
> >>From: TechNet [mailto:[log in to unmask]] On Behalf Of Peter Lee
> >>Sent: Monday, August 25, 2003 12:11 AM
> >>To: [log in to unmask]
> >>Subject: [TN] Moisture under chip capacitors
> >>
> >>
> >>Technet,
> >>
> >>I have come across a rash of failed assemblies that have 0805
> >>capacitors and resistors, bottom side glued, wave soldered
> >and washed.
> >>Trouble shooter reported touching up the solder joints on a few areas
> >>and the boards would pass test.
> >>
> >>I had a look at one board which was reported to have a 0805 56K
> >>resistor with "drifting" values. I pulled the component off
> >>mechanically in order not to apply any heat and noticed several
> >>mini-voids within the adhesive body. I have seen solder bridge within
> >>the glue before but this was the first time I saw wet residue within
> >>the voids.
> >>
> >>You can view a sample image from Steve's web site:
> >>http://www.stevezeva.homestead.com/files/SMTAdhesive.jpg
> >>
> >>The
> >>image showed the bottom side of the cracked resistor after removal
> >>(white), with a portion of solder mask (green) and SMT adhesive (red).
> >>
> >>I used a 8mil stencil. The thermal profile was verified and conformed
> >>to the slope/ curing specs.
> >>
> >>Has anyone seen this before? Any explanation as to how the void was
> >>formed and how moisture got tapped in? Does anyone re-use
> >their glue on
> >>the line or throw away any left-over to avoid moisture in the glue?
> >>
> >>
> >>
> >>Rgds,
>
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>

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