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March 2014

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From:
Mike Fenner <[log in to unmask]>
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Date:
Wed, 12 Mar 2014 23:40:07 +0000
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Well all soft solders change in service to a certain extent. As to which
changes the most and how much does it matter, it rather depends on the
criteria you are evaluating and the stressing you expose them too. Generally
you would expect changes in alloy structure to decrease with an increase in
MP for a given thermal regime. How close you get to the alloy MP is another
way of expressing that. 

Regards 
 
Mike 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dennis Fritz
Sent: Wednesday, March 12, 2014 10:17 PM
To: [log in to unmask]
Subject: Re: [TN] Solder Joint Interconnect Pull Strength Tests - Standards?

AND, I understand one of the wonderful properties of SAC solder joints is
that strength changes with aging history.  At least, that SAC changes more
than eutectic solder.  Sooo, besides the method of making the joint, you
should test strength at some simulation of the expected use conditions late
in the life of the assembly.   Can you say - long term reliability?  Maybe
that is another reason standards for joint strength are not made.  

Denny Fritz


-----Original Message-----
From: Mike Fenner <[log in to unmask]>
To: TechNet <[log in to unmask]>
Sent: Wed, Mar 12, 2014 5:01 pm
Subject: Re: [TN] Solder Joint Interconnect Pull Strength Tests - Standards?


Everyone likes a number to work to especially if it  comes with an
ISO/IEC/IPC imprimatur. Don't believe you will find one. 
Some people do torque testing on components and you might find some
indicative data for that.
So I suggest the "applicable specification" would be what ever you write.
There are any number of variables in this including how the joint was made
and then what it has seen in service. The testing I am aware of is always to
show difference between finishes or process methods or in-service changes.
Stuff like that.
To write a specification you would need to establish what your statistical
norms are and then work to some percent of those. That would give you an
inspectable criteria. [Keeping in mind that any half decent solder joint
should be several times the strength of what ever is holding the pad to
laminate. So any destructive testing should produce failures in that bond
line.] 
Care needs to be taken when setting up a test and measuring procedure to
actually do a sheer test or tensile test and not go into a peel test which
will give you a fright with very low numbers. 
Given you have a controlled and verified process I don't think you need to
write to assess every type of solder joint in an assembly, but select joint
/component type(s you can easily test as representative for the defined
process conditions.
When looking at published data for solders you need to be aware that the
properties published are derived from standardised test pieces. The results
are again really comparators in other words, not necessarily what you will
find in SMT world. 


Best Wishes
 
 
 
Mike-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of MacFadden, Todd
Sent: Wednesday, March 12, 2014 4:04 PM
To: [log in to unmask]
Subject: [TN] Solder Joint Interconnect Pull Strength Tests - Standards?

Is anyone aware of standards for conducting and evaluating lead pull tests,
and are there typical expected lead pull (or push) values for the common
interconnects (i.e., gull wing, castellation, BGA, chip cap terminals, etc).

Perhaps there are too many variables -- e.g., type, finish, configuration
and size of the lead; solder type, etc. -- to establish standard pull
strength values. We've always just used relative comparison of values from
sample lots against controls, but I'm wondering if there are typical
expected pull strength values from industry we can reference.

I noted from MIL-STD-1580B: 10.1.1.2 Terminal strength. Perform a lead pull
strength test on all parts (two parts minimum) in accordance with the
applicable specification. But what is the "applicable specification" being
referred to here?


Thanks in advance!
Todd MacFadden


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