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Date: Tue, 27 Aug 1996 13:50:55 -0700
From: Larry Waksman <<a href="/scripts/wa.exe?LOGON=A3%3Dind96%26B%3D--%26E%3D7bit%26L%3DTECHNET%26P%3D9653572%26T%3Dtext%252Fplain" target="_parent" >[log in to unmask]</a>>
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Subject: Re: Glue and Fine Pitch Devices
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Doug McKean wrote:
> 
> We are currently having our board assembly house use a quick drying glue
> to secure a 30AWG wire to the pcb for a modification.  We are finding
> the glue can cause electrical problems (not all the time) if it is
> in the leads of FINE PITCH surface mount devices.  This is confirmed
> when the glue is removed.  There is the telltale white residue on the
> glue indicating the glue is applied first and the accelerater applied
> second.  Something I've done myself.  It's my understanding that the
> accelerator should applied first and the glue second.  There are no
> controlled impedence issues and comparativley low frequency of
> 1 to 32 MHz digital signals.
> 
> 1. Has anyone had electrical problems with glue in the leads of
>    fine pitch devices?
> 
> 2. Can the glue be conductive for at least fine pitch devices?
> 
> I've seen this glue used tons of times without this effect.
> Thanks in advance.
> 
> Doug
> --
> 
> *******************************************************
> Doug McKean
> <a href="/scripts/wa.exe?LOGON=A3%3Dind96%26B%3D--%26E%3D7bit%26L%3DTECHNET%26P%3D9653572%26T%3Dtext%252Fplain" target="_parent" >[log in to unmask]</a>
> -------------------------------------------------------

As Gregg Klawson mentioned in his reply, it seems that you have some 
blooming of cyanoacrylate occurring.  You can minimize/eliminate it by 
speeding up the cure or using a low-blooming CA.  You can speed things up 
by pre-applying accelerator to the substrate and post-applying 
accelerator to the adhesive dot.  Increased humidity also helps.

Another option is to use a high viscosity, low intensity UV curing 
adhesive to tack the wires.  

Loctite has a full line of UV and low bloom CAs to help you with this.
You can reach Loctite at 1-800-LOCTITE.

Also, Gregg mentioned electromigration as a problem with surface moount 
adhesives.  Loctite also has surface mount adhesives that meet Bellcore 
TR-NWT-000078 electromigration specs. 

Good Luck,

Larry Waksman

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