Contract Electronics Manufacturing and PCB Assembly Blog

Improving Quality in SMT Manufacturing Through Moisture Control

Posted by Laura Austin on Tue, Sep 18, 2012 @ 07:00 AM

smt manufacturingSMT manufacturers should be aware that there is a tendency for plastic-encapsulated components to hold in moisture. While various steps can be taken to limit the effects of moisture in the environment, it is inevitable that a semiconductor manufacturer or OEM may still experience some of the issues related to trapped moisture. When moisture is trapped in this way, it leads to rapid thermal expansion that can damage equipment and leave an SMT manufacturing task compromised.

This damaging incidence occurs when the moisture trapped within plastic packaging is exposed to a VPR (vapor phase reflow) process, infrared soldering, or any other manufacturing process that involves quick duration high-temperature exposure. The worst side-effect of such internal damage comes in the form of tiny, threaded cracks that appear in the external package. This is known by many manufacturers as “popcorn phenomena” as it causes bulging and actual popping sounds. It can be a very costly occurrence during SMT manufacturing that is attributable to a large percentage of customer returned defective units.

Preventing Moisture Related Issues in Your Componentssmt manufacture packing

Moisture sensitivity levels are ultimately determined by the type of component, and different methods of dry packing are typically used to minimize the exposure of semiconductors to water molecules.

In-order to avoid damage during SMT manufacturing, one of the most common methods is the minimization of exposure to moisture during storage and shipping procedures of individual parts. This may include working with desiccant materials, moisture barrier bags, and humidity indicator cards that are applied to each part and can be used to monitor the accumulation of moisture, allowing personnel to take action if the moisture extends beyond a safe threshold.

Most humidity cards can be monitored with various color gradients that indicate fluctuating moisture levels. The gradients are determined at levels such as 10%, 20%, and 30%, indicating the corresponding humidity levels. If any of these indicators turn from blue to pink, it means that humidity levels have risen to an unsuitable level, and further preventative measures must be taken, such as the baking of the part in a nitrogen chamber to remove humidity.

One of the most important parts of dry packing SMT manufacturing materials is the moisture barrier bag. Such a bag requires various measurements in-order to remain compatible with the operation, and this includes a specific water vapor transmission rate, a high-level of puncture resistance, and overall strength of the material to ensure the effectiveness of its water prevention capabilities. These small bags are used to store each individual part. 

Ensuring Dry Packing is Effective

moisture sensitiveHowever, the previously mentioned techniques are of little use unless special considerations are taken to ensure your moisture barrier bag is the most effective during the SMT manufacturing process. The supplier of the components must take special consideration to ensure anti-moisture techniques are used, and subsequently the SMT manufacturer must ensure that the same strict protocol is continued at the assembly location. Components must be carefully reinserted into the bags after handling, the humidity tags must remain attached to the part, and a log should be compiled of the time and date each component is removed from a humidity bag, as well as the humidity levels before and after the component is taken from the bag.

Finally, manufacturers must be certain to re-bake components at 125 C for 24 hours using a nitrogen chamber if a component is exposed to moisture. This will ensure the component is as dry as possible before the manufacturing process is resumed. 

In Summary

By implementing consistent dry packing techniques, and being aware of the threat that moisture poses during the SMT manufacturing process, it’s possible for you to minimize, or even completely prevent, the dreaded “popcorn” effect on semiconductor surfaces and various other components. For more information, it’s best to contact manufacturers of humidity gauge technology for the latest updates about dry packing techniques and how ensure the integrity of your components.

Topics: product assembly, contract manufacturing, contract electronics manufacturing, smt manufacturing, moisture control, dry packaging