End of Life Notices That Take One Package and Spare Another
When component vendors end leaded packages, identical active silicon dies often survive in surface-mount forms that demand revised land patterns and thermal layouts.
MSL Level
Sensitivity Classification
Classification systems rank the susceptibility of surface mount devices to moisture induced damage during the high temperature cycles of solder reflow. The msl level rating for an electronic component dictates the amount of time the part can be exposed to ambient air before it must be mounted and soldered. This standard is defined by the j std 020 document, which is used by semiconductor manufacturers to characterize their products.
Moisture from the atmosphere can be absorbed into the plastic packaging of an integrated circuit. When the component is heated during the reflow process, this trapped moisture turns into steam and expands rapidly. This internal pressure can cause the package to crack or delaminate from the silicon die, a failure mode often referred to as popcorning.
Moisture Absorption
Testing for the rating involves a series of soak cycles at specific temperatures and humidity levels to simulate real world storage conditions. A component rated as level one is considered insensitive to moisture and can be stored indefinitely at room temperature. Higher levels, such as level three or level five, have much stricter requirements, with allowed floor lives ranging from one week down to just a few hours.
Once the component is removed from its protective moisture barrier bag, a clock starts ticking. If the floor life expires before the part is soldered, it must be returned to a dry storage environment or undergo a baking procedure to remove the moisture. This process is essential for maintaining the structural integrity of the solder joints and the package itself.
Floor Life
Management of the exposure time is a critical task for the assembly line operators and the quality control team. Each reel of components should be labeled with its msl level and the date and time it was first opened. If a production run is delayed, the parts must be placed in a dry cabinet where the humidity is kept below five percent to stop the absorption process.
If the time limit is exceeded, the parts are no longer safe to solder and must be baked in an oven for several hours or days depending on the thickness of the package. This baking step is risky because it can oxidize the leads and make them harder to solder, leading to a different set of quality problems. Proper tracking and storage are the best ways to avoid these complications.
Baking Procedure
Verification of the dryness of a component is done using a humidity indicator card placed inside the original vacuum sealed bag. If the dots on the card have changed color, it indicates that the seal has been compromised and the parts may have absorbed moisture. The msl level system provides a clear set of instructions for the manufacturer and the customer to ensure that the hardware remains reliable.
It is a standard part of the quality assurance process in every high volume electronics factory. By following these rules, companies can prevent costly field failures and ensure that their products have a long and stable service life. Proper moisture management is a hallmark of a professional manufacturing operation.