Phil,

Unfortunately I have been banned from my Lab and research papers [you
invent one little universal solvent (we're still trying to contain it)]
so I can't give the formulas. I will give you this saying of mine "time
wounds all heels". Given that all other things being equal, the
implications are as follows:

*         Forget about the toe fillets

*         Some believe that with Lead-free, heel fillets are over-rated

*         All heel fillets will eventually fail

*         Minimizing stress/strain relationships in the solder
connection = life

*         Height = compliancy = life

*         High ratio of lead length to cross-sectional area = compliancy
= life

*         Ductility is your friend

 

We have tested 160 pin and higher QFPs with Class 2 heel fillets and the
met our 25 year/life reliability requirements.

Dewey 

 

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro
Sent: Wednesday, August 24, 2011 1:58 PM
To: [log in to unmask]
Subject: [TN] Gull Wing Lead - no heel fillet

 

Hypothetical situation:

 

Gull wing lead, land pattern error, zero heel (also zero toe) fillet.

Hardware would not meet Class 3 workmanship requirements.

 

An equation is being used to decide if the pad to gull wing lead lap

solder joint is adequate to survive the intended thermal cycling

environment.

 

This would have been a question for Werner but I am sure there are

others here who can shed some light on this for me.

 

I know that part of the justification for why we have set our IPC

standards where they are is partly based on years of testing.

 

How could a mathematical calculation such as "Steinberg equation"

justify a lack of Class 3 gull wing lead heel fillet?

 

Any help is appreciated.

 

 

 

 

 

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