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,
>>Peter
>>
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