Hello Leland,

There are a couple of potential issues when using solder paste that has been thermally stressed.   Reactions between the flux and solder powder are accelerated by heat.  Some solder pastes are not stable at room temperature, and higher temperatures can cause dramatic degradation in performance.  

If the viscosity is within specification, then the solder paste will likely print fine.  The stencil life may be shortened, so the print characteristics of the paste may worsen more quickly than normal.   The solder paste may also have issues in reflow.  Wetting may not be optimal, and you might see solder balling and graping issues.   

I agree with a previous response that it is best to check with your supplier before using the solder paste.  


Best regards,

Tony Lentz
FCT Assembly
Field Application

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Friday, June 5, 2015 11:06 AM
To: [log in to unmask]
Subject: [TN] Solder Paste Question

Everyone,

We just received 25 tubes of solder paste that got misplaced by the carrier and was delivered in 6 days instead of the usual two.  When it arrived it was warm to the touch.

We performed a viscosity test after allowing it to stabilize to ambient, and the readings returned were within spec and very close to our typical results.

Is there any danger in using this shipment?

Thanks for your help!

Leland

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