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July 2010

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Subject:
From:
Ashok Dhawan <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Ashok Dhawan <[log in to unmask]>
Date:
Mon, 5 Jul 2010 22:50:08 -0500
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Werner

I am having limited info and am looking from experts on technet to provide
guidance using limited info when to rework and when to let go.

If device is tilted, the thickness will be different from one end to other
end. what basis to use for rework for tilt ? My own guess is it can be based
on minimum thickness, if it was within acceptable range of thickness, tilt
will be acceptable.

I am urging all technet experts to share their experience on this subject.   


Answers to questions are listed below :  

The minimum solder joint thickness depends on 5 parameters:
(1) the size of the QFN,------ QFN-32 is 2 mm x 2 mm Package with 10x 19 mil
signal pins and 120 x 120 mils cooling plate.
(2) the CTE-mismatch with the PCB,-----Do not know. It is plastic
package,board is FR4 , soldered with Tin-lead solder.Peak treflow is 225-230
deg C.

(3) the delta-T, -----the operating temperature range for the product is -55
deg C to 125 deg C. I do not know junction temperature range.
  
(4) the reliability requirement in terms of number of cycles, and

---- Do not know. The expected life of product is 5 to 10 years.

(5) the reliability requirement in terms of acceptable failure probability.
------ Do not know.

How all of this hangs together, can be found in IPC-D-279; alternatively,
you can take my workshop on fundamentals of solder joint reliability.

---------- Please provide me info if there is an upcoming webtorial on this.



 Regards

Ashok Dhawan, P. Eng. 
Manufacturing Specialist 
Parker Hannifin Electronic Controls
Electronic Controls Division
1305 Clarence Avenue
Winnipeg, MB  R3T 1T4 Canada
direct 204 453 3339 x390 
fax 204 452 6801 
[log in to unmask]
www.parker.com/ecd

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