Voiding Control Beneath Bottom Terminated Components using Solder Fortifications® PreformsAuthors: Derrick Herron, Christopher Nash, Raymond Luo, Andy Wei
Company: Indium Corporation
Date Published: 4/21/2015 Conference: SMTA China
One of the biggest challenges facing the electronics industry today is voiding in the solder joints that connect bottom terminated components to PCBs. This solder voiding, especially on thermal pads, can lead to hot spots and a reduction in the life of the component and the overall assembly. Limited improvement is gained from making modifications to the profile and solder paste alone. Without careful design considerations, it is also difficult to obtain precision in the level of voiding from one component to another. In the past, thermal pad design and the use of thin, custom-sized solder preforms placed into solder paste at the thermal pad have been studied. This paper looks at a new approach using readily available solder fortification® preforms. These preforms are automatically placed into the paste of the thermal pad before the QFN component is placed, forcing the component to sit at an angle to allow for outgassing of flux during reflow before the solder fortification preform melts, then allowing the component to come to rest in its final desired orientation.
It has been determined that this approach can both decrease the level of voiding found in the solder joints beneath bottom terminated components and also decrease the amount of variation in this value. While this paper focuses on this technique when used with SAC305, it is versatile enough to be used with other alloys commonly available in paste and solder fortification preform forms. This method also has the added benefit of being fully compatible with current manufacturing processes, adding only extra placement steps without the need to change reflow profile, equipment, etc. This easy and inexpensive modification to current processes can have a big impact on the reliability of the final product.
QFN, bottom termination, void, preform, solder fortification preform, solder paste
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