OK International - Dual Preheater Rework System Prevents Damage to Dense Lead-free Assemblies

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By Ed Zamborsky and Paul Wood

Advances in PCB and component technology have created higher demands on the equipment used to repair and rework array components. It is no longer possible for the operator to simply increase the reflow temperature and expect safe and controlled component removal. These uncontrolled operators can damage the latest lead‐free assemblies by utilizing older and less capable rework systems.

PCB Technology

The latest generation PCBs are becoming more complex as customer demand drives them to smaller and more compact footprints, one of the most common devices; the smartphone/PDA has increased its functionality while becoming more user friendly and much smaller. To design these devices, the industry has responded by increasing the PCB thickness to accommodate the increased I/O density of BGA and stacked BGA devices. In addition, to control the thermal energy they have been forced to increase the number and weight of the embedded ground planes. This results in high cost and high density boards with very demanding rework applications. As an example, current 3G and 4G phones are being produced with up to 12 copper layers, while larger server boards can have up to 24 layers of copper. This means that more heat capacity is needed to reflow and rework these PCBs, while the temperature maximums for the component lids remains the same at 260°C, which in turn is very close to the melting temperature of the internal materials used to assemble them.

Component Technology

The BGA solder ball pitch is constantly evolving downward. For example, a typical 35mm square BGA with 1.27mm pitch has a ball count of 680. Today that same package size with a pitch of 1.00mm now has a ball count of 1156 balls. This increase of package density requires 40‐50% more heat capacity to safely rework the part. In the era of leaded solder, an operator...

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