Jim,
Regarding the use of a test die in the BGA. It depends on what you are 
looking for in your test program. For BGA devices the presence of 
silicon does affect the joint reliability. The low Cte of the silicon 
seems to concentrate strain at the solder joints directly below the 
edge of the die. The joints that fatigue fail first tend to be the 
corner joints and the joints below the edges of the die. If all you 
are looking for in your testing is assembly solder joint reliability 
under temperature cycling conditions then a full test die is not 
needed. All the BGA needs is non active silicon and daisy chain 
connections to allow you to monitor joint integrity. Daisy chained 
dummy BGA components with no functional silicon are available off the 
shelf from Topline Components as well as vendors of BGA's for assembly 
process development. 

A full test die is useful if you are interested in getting power 
dissipation data for the BGA, or the board and system design, They can 
also be used to get stress, and humidity reliablility data for the BGA 
design. Apparently calibrating on silicon strain gauges and and 
humidity sensors is difficult, though I have not done this myself. Use 
of on silicon heaters and temperature measurement works very 
satisfactorily. The heaters  can be used for power cycling and the 
junction temperature can be measured in the finished design. This is 
useful for checking the results of thermal models. 

    Whether you need to use test die depends on what sort of business 
you are in. Using a full test die will add cost and time for 
procurement and packaging. If all you are interested in is solder 
joint life, then I don't think they are worth the extra. 

Jeremy Drake
Design to Distrbution Ltd.
Stoke on Trent, England. 


Original Message>>
================
This is a re-submittal.  Apparently 1st one didn't make it out.

I have heard of special test die (ie. silicon) developed to support
reliability testing of surface mount solder joints; especially LCCs 
and
BGAs.
These die typically did continuity but also included other features 
such
as 
* power cycling capability
* strain gage measurement of stresses on die
* ability to measure (on die) temperature and/or humidity/moisture
content 

We are beginning to layout a test vehicle for BGA efforts and want to
include
a die in the vehicle (based on the literature that the die 
significantly
effects the strains in the part during temp cycling and thus it's 
"life)
and
were considering using some special die (assuming that they were
available).
We assume we would have to pay to have these die "mounted" and wire
bonded
into the BGA vehicles we plan on testing.

My questions are:
a) Does anyone have any experience with using these "special test die"
in
    life testing for SMD joints?
    If so, in hindsight was the "extra expense" worthwhile or not??

b) Does anyone know of any sources for the die?  P/Ns? Capabilities
(e.g.
    continuity, powercycling, etc).

Thanks for your time.
===============================
Jim Maguire
Senior Principal Engineer
Boeing Defense & Space Group
PO Box 3999  M/S 3W-97
Seattle, WA  98124-2499
Phone (206)657-9063     Fax 657-8903
Email:  [log in to unmask] 
================================

===============================
Jim Maguire
Senior Principal Engineer
Boeing Defense & Space Group
PO Box 3999  M/S 3W-97
Seattle, WA  98124-2499
Phone (206)657-9063     Fax 657-8903
Email:  [log in to unmask]
================================

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