July 25, 2012

Protecting Moisture-Sensitive Devices, Part I

It goes without saying that water and electronic components do not mix. But even the absorption of the tiniest bit of moisture from the air can damage delicate surface mount devices and other electronic components enclosed with plastic compounds (moisture-sensitive devices, or MSDs). Often, this damage is invisible to the naked eye – which could result in substandard parts being used in production, then causing major problems for a manufacturer (and/or end users) down the road. This is why Converge closely monitors and addresses the moisture sensitivity level of every MSD order that comes through our warehouse as part of our 76-point quality inspection

The problem with moisture absorption and retention inside a component is that the trapped moisture becomes steam when the device is subjected to sudden high temperature, such as during reflow soldering. This applies tremendous internal stresses to the package, which can result in separation (delamination) of the plastic from the die or lead-frame, wire bond damage, die damage, and internal cracks. In severe cases, cracks will extend to the component surface or the component can even bulge and pop. This is known as the “popcorn” effect. When a component cracks or buckles after it has been mounted to a board, it destroys the entire board. Thus, one small part can put an entire production line down, resulting in thousands or even millions of dollars in damage. 

Two industry standards help electronics manufacturers and distributors tackle the challenges of moisture sensitivity: IPC/JEDEC J-STD-020B and IPC/JEDEC J-STD-033B. The IPC/JEDEC J-STD-020B standard defines the classification level of nonhermetic solid state surface mount devices that are sensitive to moisture-induced stress. Generally, the smaller and thinner the package, the more quickly that moisture can reach the most critical areas of the component. The chart below shows the eight sensitivity levels of MSDs, with 6 being the most sensitive: 


The “floor life” is the length of time at each level an MSD can be exposed to ambient room conditions (approximately 30°C/60%RH) before being mounted and reflowed. This presents an added challenge to independent distributors, who often process orders that are no longer in original factory packaging. 

When an MSD order arrives at Converge, the packages must be opened so that components can be properly inspected for any kind of discrepancy. But as soon as the packages are unsealed, the exposure clock starts ticking. Converge inspectors use the MSL chart as a guide to determine how to properly protect components before shipping them to our customers. To find out more about how we do that, including our in-house baking process, read "Protecting Moisture -Sensitive Devices Part II of this series now.

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