Authored By:
Paul Wood
OK International / Metcal
Summary
The industry continues to face the challenges associated with BGA, QFN/BTC, and LED packages. The demand for more performance by consumers drives change, which results in greater component density. Component density on printed circuit boards continues to decrease with a corresponding increase in component complexity and reduction in pitches. Good examples of these industrial trends are smart phones, tablets and wearables.
In modern production lines, the complexity of these devices drives manufacturers to rely on automated equipment and strict production processes to control variables such as paste deposition volumes, reflow times, and component placement when working with new boards. However, in a rework scenario, controlling all of the variables required to remove and replace one component is challenging. Each of the variables involved with soldering these devices require management on an individual basis. Herein lies the challenge.
Many rework processes are still manual ranging from hot air pencils to automated rework machines. These tools are required to duplicate the production process on an individual level. Solder balls up to one thousand I/O and a pitch of 0.35mm on a BGA are becoming more common than 0.4mm or 0.5mm in a package size of 14mm square. QFNs, traditionally, are difficult to rework due to their excellent thermal characteristics. QFNs with a 0.35mm pitch and double row terminals on the perimeter and various size ground pads in the middle are increasingly common. LED technology has seen a massive growth, with larger packages and higher wattage output in today's leading edge printed circuit boards. Higher wattage output requires the use of metal backplanes to dissipate the heat. Contrast the backplane requirement with a relatively low temperature lens and the challenges become evident. This requires more thermal energy in rework without melting the case of the LED. This is a different situation to when LEDs first became mainstream. This paper will show rework processes for all of these challenging components.
Conclusions
Successful rework encompasses three key points. Component removal without damage to the printed circuit board or adjacent components, preparing the lands for component replacement and replacement of the component. BGA, QFN/LGA, and LED packages have been in use for years. The challenge in rework is the improvements made to these packages over those years that continues to increase the challenges associate with rework. Process control via documentation, process, andcontrol and the correct tools and fixtures are critical to success. The need for operator training is equally important as the complexity of parts continues to increase and utilization in the industry is broad. Successful rework is possible with an understanding of all the rework challenges.
Initially Published in the IPC Proceedings
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