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A G R E AT E R M E A S U R E O F C O N F I D E N C E observed include heat-stress re-crystalliza-
tion, thermal stress, and voltage drops under
conditions of constant electrical power input
(Joule heating effects).
Another area that requires much test-
ing grows out of new electronics packaging
technologies. Ever-advancing electronics
packaging technology drives a need to per-
form testing of higher and higher density in-
terconnects. With hundreds of test points in
Speed Up Testing
a large ball grid array (BGA), it has become
impractical to test each point sequentially,
yet accelerated life testing requires indepen-
with Simultaneous
dent testing of each ball. A concern for BGAs
is electromigration due to current crowding,
which requires individual electrical control
Sourcing to maintain constant Joule heating as well as
measure interconnect resistance. The chal-
lenge is to do all this testing in a reasonable
(affordable) length of time, and the solutions
tend to involve simultaneous sourcing.
Pete Hulbert and Paul Meyer, Keithley Instruments, Inc.
Simultaneous Testing Strategies
T
Simultaneous source testing of a large
ESTING is a vital step in electronic latest lead-free solder techniques and analy- number of DUTs requires consideration of
production, but it takes time and sis of wear-out mechanisms in modern elec- the trade-offs among practical parameters,
money. Anything that can speed up tronic packaging, particularly in structures such as cost, rack space, throughput, and
the process is welcome, and one of like fine-pitch ball grid arrays (BGAs). We'll precision. Current test equipment offers a
the most obvious methods is to use look at both. wide range of simultaneous testing strate-
simultaneous sourcing--driving several de- By statute, lead is being phased out of gies, including:
vices under test (DUTs) at the same time and electronic equipment of all types. While Source-Measure channel per DUT--
with the same voltage or current and reading this may reduce the amount of toxic lead in This strategy provides independent source
the results for all. Simultaneous sourcing is the waste stream from discarded electronic control and measurement for each DUT
used when the test application requires in- equipment, it presents manufacturers with (Figure 1). As a result, it is possible to use
dependent source control and/or continuous significant problems. The characteristics of measurement feedback to maintain constant
monitoring of multiple DUTs. It becomes Sn-Pb solders are well understood, but the source adjustments (for constant Joule heat-
more important for throughput when the test various alternatives--including high-tem- ing applications) and high sampling rates to
is lengthy, as is the case for accelerated life perature (250