东芝电子可靠性测试(23)

东芝电子可靠性测试

2.4 Temperature and Humidity

2.4.1 Moisture Resistance Tests

Most semiconductors devices of recent years are encapsulated in plastic resin. The reliability of these devices largely depends on the moisture resistance of the package. Various types of moisture resistance evaluations tests have been developed in order to evaluate these devices quickly. Table 2.2 shows examples of these moisture resistance evaluation tests.

The tests are largely divided into two groups. The first group places the device in a humid atmosphere, and the second group applies bias to the device while subjecting it to humidity or after moisture has penetrated into the device. The device classification is made according to the device type (such as the level of power consumption) and the type of failure mechanism to be detected.

If the acceleration rate is too fast, humidity resistance testing can produce failure modes that are different from those that appear during actual usage or problems related to test reproducibility may arise. Therefore, extra care must be taken when performing these tests. Particularly with saturated type PCTs (pressure cooker tests), unexpected failure modes that will never occur in the field (for example, pin-to-pin migration on outer leads) can occur because the device may be exposed to conditions in which dew is formed. Consequently, care must be taken when performing assessments or when evaluating test results.

In addition, recently the mainstream semiconductor device has become the surface mounted device (SMD), accelerating compact and thin designs one step further. With these types of semiconductor devices, the thermal stress during mounting and resin humidity absorption during storage cannot be ignored. To properly simulate actual usage conditions, the mounting stress is applied as part of a pretreatment process, and a humidity resistance test is conducted.

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