Online proceedings - EDA Publishing Association
Online proceedings - EDA Publishing Association
Online proceedings - EDA Publishing Association
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7-9 October 2009, Leuven, Belgium<br />
Regarding the study of the impact of moisture absorption<br />
taken up by the package, the same package type has been Temperature (°C)<br />
measured with four different pre-conditions, as shown and<br />
250<br />
described in Table 1. For each condition, 5 samples have<br />
been measured.<br />
200<br />
TABLE I<br />
Overview of Sample Conditions for warpage measurements<br />
Condition<br />
Code<br />
Reference structure with uncontrolled<br />
“REF”<br />
history, as they were lying for more than 1<br />
year lying on the shelf (probably, they took<br />
up some moisture)<br />
Reference structure dried for 3 days at<br />
“DRY”<br />
120°C<br />
Reference structure humidified in a<br />
“WET1”<br />
humidity chamber, for 168h at 85°C and<br />
85% humidity.<br />
Reference structure humidified in a pressure “WET2”<br />
cooker chamber, for 18h at 120°C and 100%<br />
humidity.<br />
B. Measurement setup<br />
The measurements were done with the Topography and<br />
Deformation Measurement (TDM) System from Insidix<br />
[4,5]. The out-of-plane measurements use the principle of<br />
the projection moiré technique to measure the topography as<br />
the difference between a reference horizontal surface and the<br />
measured surface. This reference surface is a calibration tool<br />
that is perfectly flat and homogeneous white and is measured<br />
beforehand. The outcome of one measurement is the out-ofplane<br />
profile, as shown in Fig. 3.<br />
The warpage is then defined as the difference in out-ofplane<br />
displacement between the center and the corner<br />
(not the difference in z-height!).<br />
150<br />
100<br />
50<br />
0<br />
0 5 10 15 20 25<br />
Time (min)<br />
Fig. 4: Temperature profile applied to PBGA sample for the<br />
topography measurement<br />
C. Measurement result for a “DRY” sample<br />
The first experiment presented in this paper is the warpage<br />
profile measurement for a dry sample. Fig. 6 shows the outof-plane<br />
profile for this package at 22°C and at 227°C (=<br />
maximum reflow temperature). At 22°C, the warpage is<br />
almost zero, while at 227°C, the warpage is visibly high.<br />
Z-height (µm)<br />
1800<br />
1600<br />
1400<br />
1200<br />
1000<br />
800<br />
600<br />
400<br />
200<br />
0<br />
227°C<br />
22°C<br />
0 10 20 30 40 50<br />
Distance from one corner (mm)<br />
Fig. 5: Out-of-plane profile (topography) measured by INSIDIX<br />
equipment (along the diagonal).<br />
Fig. 3: Topography measurement of the PBGA package<br />
B. Temperature loading profile<br />
A typical reflow temperature profile has been applied for<br />
this package, with a maximum of 227°C. The heating is<br />
performed by IR camera’s, while the temperature is<br />
measured using a thermo-couple touching the BGA sample.<br />
The warpage has been measured at different temperatures,<br />
both in heating and cooling. The result for this sample is<br />
shown in Fig. 6. At room temperature, there is a small<br />
warpage of about 50 µm (corners bending downwards). This<br />
warpage is almost constant up to 170°C. Above this<br />
temperature, the warpage substantially change and the corner<br />
start to bend downwards. This reason is that the glass<br />
transition for the overmould is reached, resulting in a high<br />
CTE mismatch between the overmould and the BT (while<br />
they are quite well matched below 170°C). As a<br />
consequence, the corners start to warp downwardsn and this<br />
becomes very high at maximum temperature (450µm).<br />
©<strong>EDA</strong> <strong>Publishing</strong>/THERMINIC 2009 114<br />
ISBN: 978-2-35500-010-2