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226 Development of A Moisture Soak Model For Surface Mounted Devices
Table 15.2 Experimental units.
Lead count 44 68 84
Die size 120 × 120 mil 148 × 160 mil 210 × 210 mil
DAP size 250 × 250 mil 280 × 280 mil 300 × 300 mil

PLCCs were manufactured. The die and die attach pad (DAP) size were maximized so
as to create a larger critical surface area and allow a higher likelihood of delamination.
These are summarized in Table 15.2.
The tests were carried out in accordance with the procedures and standard set
by JEDEC, EIA/JESD22-A112A 11 and National Semiconductor specifications. The
flowchart for a moisture absorption test is given in Figure 15.1.
Votsch temperature--humidity chambers and a Mettler precision weighing scale
were used for the moisture absorption and desorption tests. Before the actual com-
mencement of the moisture test, calibrations for all the equipment were carried out.
Since the weighing system is very important for this study, a gage repeatability and
reproducibility was carried out to ensure the capability of the weighing system.
Four samples of 20 units each were prepared for the four temperature--humidity
test conditions of 30 C/60% RH, 60 C/60% RH, 85 C/60% RH, and 85 C/85% RH.
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Good Units 0hr Test Sample size: 50 units
1 Weight Initial weight

2 Bake 24 hrs
@ 125 °C
3 Weight Ensure units are totally dry through no change in weight. Step 1 to
step 3 can be repeated with different baking duration till total dry
weight is achieved.
Weighing must be completed within 30 min after removal from oven.
Units must be sent to the moisture chamber within 1 hr after
weighing
4 Moisture Soak 6 hrs (initial)*
@ X °C/X % RH RH: Relative Humidity
5 Weight Weighing must be completed within 30 min after removal from oven.
Units must be sent to the moisture chamber within 2 hrs after
weighing
6 Analysis of Results
* For initial or earlier readings, moisture soak duration should be
relatively short as the absorption curve may have a steep initial
slope. For later readings, moisture soak duration may be longer as
the absorption curve becomes asymptotic.

Step 4 and step 5 are repeated with different moisture soak
duration until the units reach saturation as identified by no additional
increase in weight.
Figure 15.1 Flowchart for moisture absorption test.