AN610 Datasheet, PDF (1/17 Pages) Vishay Siliconix – PolarPAK Solder Joint Reliability Based on Thermal Fatigue IPC-9701

AN610
Vishay Siliconix
PolarPAK Solder Joint Reliability Based on Thermal Fatigue
IPC-9701
By Kandarp Pandya
ABSTRACT
PolarPAK, a thermally enhanced package from Vishay
Intertechnology, facilitates MOSFET heat removal
from an exposed top metal lead-frame connected to a
drain surface in addition to a source lead-frame con-
nected to a PCB. See Figures 1 and 2.
Figure 1: Top View of a PolarPAK
For a new-generation package like PolarPAK, it is im-
perative to examine solder joint reliability. IPC-9701^[1]
guidelines are implemented for PCB design and tem-
perature cycling. The latter induces thermal fatigue on
solder joints, which in turn enables the study of solder
joint reliability.
The design of experiment (DOE) consists of two
phases. The first phase is process development dis-
cussed in the application note titled "Development of
Lead-free soldering profile for PolarPAK"^[2] The appli-
cation note describes PCB design, process variables,
and process development methodology, and con-
cludes by defining a recommended process.
Figure 2: Bottom View of a PolarPAK
The second phase also follows IPC-9701 guidelines,
comprising the assembling of device samples and the
study of solder joints under thermal fatigue induced by
a temperature cycling test.
The PCB assemblies were done at a third-party ven-
dor, contract-manufacturing facility. Current industry-
standard assembly practices and equipment setups
were used for the development. This insures a smooth
implementation of results in manufacturing practices.
The assembly process recommendations derived in
the aforesaid application note were used for lead-free
solder paste. The latter includes other process vari-
ables such as stencil designs and parameters for sol-
der paste applicator machines and part pick-and-place
machines. Ramp-soak-spike (RSS) profiles for both
varieties of solder pastes were used. First, a visual
inspection was used to check for obviously faulty sol-
der joints. Both 5DX laminography X-ray and 2DX
transmission X-ray equipment were used for data col-
lection and analysis.
The thermal fatigue DOE comprises 3,000 tempera-
ture cycles from 0 °C to 100 °C for a component sam-
ple size of 32+10 (re-work) as defined in IPC-9701.
Event recording and monitoring of solder joint resis-
tances of each daisy chain joint at the end of each
cycle identifies a failure point for the solder joint. The
primary benchmark as per IPC-9701 is if no failure
occurs before 3,000 temperature cycles, in which case
the part qualifies for solder joint reliability.
Document Number 73507
31-Aug-05
www.vishay.com
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