Did you try turning the convection blowers down a bit? We noticed that
tombstones increase if you are just on the edge of moving the parts.
O508s do have a bigger terminal, and shorter rotation to tombstone. 

You might also try a thinner stencil. 

Smaller paste deposit. Bow Tie pattern . . . or combination. You need to
weaken the force enough to stop lifting the part. 


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon
Sent: Monday, January 15, 2007 2:24 PM
To: [log in to unmask]
Subject: Re: [TN] tombstoning of 0508 ceramic capacitors

	Hi Royce:
	         Have you tried two smaller dots of adhesive instead of
one larger one?  The same amount of glue would be dispensed but along
the width of the part.
	Regards,
	Ramon
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Royce Taylor
Sent: Monday, January 15, 2007 2:04 PM
To: [log in to unmask]
Subject: [TN] tombstoning of 0508 ceramic capacitors

I have a question for the "Adhesive Dispense"  OR the "0508 chip"
experts out in Technet land.

We at times struggle with 0508 capacitors tombstoning (yes, 0508 not
0805). We do run Nitrogen and turning it off helps at times but there
are many times we need to run nitrogen for other reasons. Most times we
try to dispense a dot of adhesive (Loctite 3609) but we are having
occasional issues with the adhesive getting into the solderpaste, the
gap between the pads measures ONLY 0.020" so it is difficult to prevent
this from happening.  Does anyone out there run into the same issues??
Any thoughts?? We run a Camalot Gemini and a Fuji GL dispenser and use a
25 GA needle. Also we use Indium SMQ92J No Clean solderpaste so I don't
know if this paste is contributing to the tombstoning.

A re-layout of the boards is not an option. We have tried both a
"straight ramp"  and a "ramp-soak-ramp" profile with little or no
difference.

Thanks for your thoughts and advice

Royce
*************************************************
Royce Taylor
Raytheon
350 Lowell St.
Andover, MA  01810
(978) 470-7431

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