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February 2008

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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Thu, 14 Feb 2008 07:25:33 -0600
Content-Type:
text/plain
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text/plain (80 lines)
Herminia,
Because the heel fillet is the only portion of the solder joint
(typically) that is made to the finished (flat) portion of the component
lead, it is the most critical. The toe and side fillets are formed to
exposed copper. While it is desirable to have good toe and heel fillets,
the heel is the most important.
With that in mind, a decision was made to require a heel fillet at least
half a lead thickness in height.
Having sufficient amounts of solder paste certainly improves one's
chances of obtaining a Class 3 fillet, but certainly does not gaurantee
it.
Just because you have proof that your solder thickness sufficient to
form a good solder fillet isn't good enough. Solder does not always wet
where it is supposed to, or this forum would never have existed.
JEDEC standards exist for coplanarity of component leads.  

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Herminia Guevarra
Sent: Wednesday, February 13, 2008 5:01 PM
To: [log in to unmask]
Subject: [TN] Minimum Heel Fillet Height

Hi, folks,

 

Can anybody please explain in details how the minimum heel fillet height
criteria for Class 2 was computed and specified?

 

F= solder thickness (G) + 50% lead thickness

 

Can solder thickness be solder paste height prior reflow?

 

What about if leads are not coplanar?  What would be the spec for co
planarity?  How can they be measured?

 

Need reply...

 

Thanks,

 

Herminia 

 


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