Popcorn Failures are because of moisture sensitivity of IC Packages, and thermal stress during soldering while PCB assembly. Improper storage, handling, or packaging of plastic encapsulated semiconductor devices can allow the introduction of moisture. Moisture trapped inside plastic encapsulated packages can damage them during soldering, as the moisture vaporizes and tries to expand. The expansion of trapped moisture can result in internal separation (delamination) of the plastic from the die or lead-frame, wire bond damage, die damage, and internal cracks. Most of this damage is not visible on the component surface. In extreme cases, cracks will extend to the component surface. In the most severe cases, the component will bulge and pop. This is known as the “popcorn” effect.
A plastic package contains moisture, can also result in external steam jets from the package, which may displace other nearby components on the circuit board during the solder process.
MSL Component Handling Guidelines to Avoid Popcorn Failures
In recognition of the varying degrees of popcorn cracking tendency of various package types, IPC/JEDEC defined a standard classification of moisture sensitivity levels (MSL’s). The MSL’s are expressed in numbers, with the MSL number increasing with the vulnerability of the package to popcorn cracking. Thus, MSL1 correspond to packages that are immune to popcorn cracking regardless of exposure to moisture, while MSL5 and MSL6 devices are most prone to moisture-induced fracture.
It is important to handle dry pack bags very carefully to prevent plastic packages from absorbing moisture. The following guidelines are helpful in avoiding the component failure due to moisture sensitivity.
- Moisture barrier bags are sealed at manufacturer during component packing. These bags must be handled with care to avoid puncture of tearing of the bag’s material.
- Upon receipt, moisture barrier bags should be inspected for punctures or holes of any kind. If openings in the bag are found and the maximum humidity indicator has been exceeded, the parts shall be baked according to the conditions specified by manufacturer.
- Bags should remain sealed until parts are ready to be used.
- Inspect the humidity indicator card (HIC) immediately after opening the package and evaluate the colors of the dots. The HIC card color should be blue (dry).
- Proper handling of storage, board mounting assembly and rework is critical to avoid over-exposure of the package to moisture.
IPC created and released IPC-M-109, Moisture-sensitive Component Standards and Guideline Manual.