Continuation of the previous PCT test purpose and application (2)
The way water vapor enters the IC package:
1. Water absorbed by IC chip and lead frame and silver paste used in SMT
2. Moisture absorbed in the plastic sealing material
3. The device may be affected when the humidity in the plastic sealing room is high;
4. After the encapsulation of device, water vapor permeates through the plastic sealant and the gap between plastic sealant and lead frame, because there is only a mechanical combination between plastic and lead frame, so there is inevitably a small gap between lead frame and plastic.
Note: As long as the gap between sealant is greater than 3.4*10^-10m, water molecules can pass through sealant protection
Note: The airtight package is not sensitive to water vapor, generally do not use accelerated temperature and humidity test to evaluate its reliability, but to measure its air tightness, internal water vapor content, etc.
PCT test description for JESD22-A102:
It is used to evaluate integrity of non-airtight packaged devices against water vapor in water vapor condensation or saturated water vapor environments. The sample is placed in a condensed, high-humidity environment under high pressure to allow water vapor to enter the package, exposing weaknesses in the package such as corrosion of the delamination and metallization layers. The test is used to evaluate new package structures or updates of materials and designs in the package body. It should be noted that there will be some internal or external failure mechanisms in this test that do not match the actual application situation. Since absorbed water vapor reduces the glass transition temperature of most polymer materials, an unreal failure mode may occur when the temperature is higher than the glass transition temperature.
External pin tin short circuit: The ionization effect caused by moisture in the package external pin will cause abnormal growth of ion migration, resulting in short circuit between pins.
Moisture causes corrosion inside the package:
The cracks caused by the moisture through the packaging process bring external ion contamination to the surface of wafer, and after passing through the surface defects such as: protective layer pinholes, cracks, poor covers...Etc., into the semiconductor original, causing corrosion and leakage current... Such problems, if there is applied bias then the fault is more likely to occur.
PCT test conditions:
(Sorting PCB, PCT, IC semiconductor and related materials have relevant test conditions on PCT[steam pot test]) PCT test purpose and application
