Hello Steve?.

I assume that the soldering process window is wide enough for the actual 
product that the question originate from.

My general opinion is that there is no difference in solder strength 
irrespective of the annular ring. It is not the amount of the solder that 
is determining factor when considering the strength of a solder joint but 
the molecular structure in the solder itself.

Strength on the other hand, is varying depending on materials involved. 
For instance, if U have gold involved in a solder joint, the bond between 
Au-Au or Au-Ni atoms are weaker the between Pb-Pb or Sn-Cu atoms? 
And to make it worse? There is ALWAYS a dedicated intermetallic layer 
inside the solder joint that is weaker then anything else around. 
Therefore I if U put a constant mechanical force of, we say only 20-30N, 
to the solder joint, it would collapse soon or later due to abnormally 
rapid aging in just that weak layer.
The concrete example is if U have a contacts (for example D-Sub) on the 
PCB that are mechanically fixed to the instrument back plane at the same 
time as the PCB is mechanically attached to the other parts of the 
instrument and if the tolerances in the design are not wide enough, the 
solder joint is going achieve a fatigue limit causing a collapse as a 
consistency of a mechanical force applied to the soldering joint.

I agree with Werner when we talk about solder strength in relation to its 
purpose.
Soldering joints within electronics are not thought to act as welding 
points.

U can relate the question to "Is SMD joint weaker then THD joint?" It is 
the same principle.

And U can read the contribution that Ingmar made in Reliability Solder 
discussion with a similar Real-Life example.

The direct consequences with a larger annular ring are only positive in a 
terms of higher process(soldering) reliability (soldering, ev. printing, 
rework, inspection and so on).


*************************************************************************
Sasha Miladinovic - Production Engineering 
Amersham Biosciences, PCB Production, Umeå
Tel:      +46 (0) 90 150 232
Fax:     +46 (0) 90 138 372
E-mail: [log in to unmask]
*************************************************************************





Steve Kelly <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
2003-10-23 23:56
Please respond to "TechNet E-Mail Forum."; Please respond to Steve Kelly

 
        To:     [log in to unmask]
        cc: 
        Subject:        [TN] Solder Joint Strength


I had a question from a customer today which I could not answer. Question 
was " if a pin is soldered in a through hole with an annular ring of .010 
is this a stronger joint than if the annular ring was .005" . Doesn't this 
depend more on the soldering technique that the size of the ring? Thanks. 
Steve Kelly
 
PFC Flexible Circuits Limited
Ph: (416) 750-8433
Fax: (416) 750-0016
Cell: (416) 577-8433
E-Mail: [log in to unmask]
 
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