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Written by Dr. Renzhe Zhao
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Monday, 30 June 2008 19:00 |
New silicone technology can add support and vibration dampening for demanding applications.
Connecting and disconnecting control boards. Plugging and unplugging cables into computers. Constant vibration onboard automotive modules and construction equipment. All these conditions can wreak havoc on electronics devices, significantly reducing performance or rendering them completely inoperable. To help ensure against bent leads, damaged components from vibration or material degradation inside particularly harsh environments, additional stability is often required. But, delivering this stability in a material medium that cures quickly, integrates seamlessly inline, is easy to use and aesthetically appealing is a tall order.
Traditionally, hot melt glues have been used to achieve the desired stability and protection. And, while these materials may offer some stress relief, they are extremely difficult to use. In most cases, the glues have to be applied manually. They are also messy in a production environment and can pose a safety hazard as burns are prevalent when using these materials. From a performance perspective, there are also challenges. Hot melt glues are more difficult to dispense, so material placement isn’t always precise. In addition, their relatively high ionic content may pose corrosion issues and, ultimately, failures. Finally, because the majority of hot melt glues are thermoplastics, not thermosets, when used in high temperature environments such as automotive applications, these glues may melt and flow away or significantly weaken, again having a negative impact on performance.
New silicone technology, however, has emerged as a cost-effective and reliable way to deliver the added support and vibration dampening required for many of today’s most demanding applications. This new class of materials are fast-curing, noncorrosive room temperature vulcanization (RTV) silicone materials designed for a variety of uses including wire tacking, selective sealing, vibration dampening and rework/repair on PCBs. With extremely fast dispense times – as little as 31 sec. for two connectors – and a tack free time of less than 5 min., next-generation silicone technology offers manufacturers a high UPH alternative to other materials. Most are also highly thixotropic, so the materials will hold form upon dispense and not spread or migrate to other locations where material is not desired. The silicone systems cure at room temperature, so no additional equipment investment is required to integrate them into the production environment.
Other benefits of this material class includes excellent shear strength to prevent any pull back from the component or the board. Adhesion is outstanding, permitting a strong and lasting bond to a variety of finishes. And, these products are thermally superior. Unlike hot melt glues or older generation silicone materials, the newer generation silicones are extremely robust and ideal for high temperature environments such as automotive applications. They will maintain their strength, shape and color even in the most severe environments. Further, the flexibility of the silicone matrix is more supportive for delicate electronics components as compared to hot melt alternatives. Aesthetically, the more recent silicone formulations are also superior (Figure 1). The clear, translucent appearance of the products are far more appealing than the yellow-brown color of other silicone materials.
Dr. Renzhe Zhao is technical manager, applications engineering at the electronics group of Henkel (henkel.com);
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