Bottom Termination Component
05 November 2010
There are many components that fall into this category and are simply semiconductors that have termination/solderable areas fully under the body of the component or protruding to the edge of the component.
Land Grid Array (LGA), Quad Flat No Lead (QFN) are the most well known examples of this style of part. In the case of LGA and QFN style parts the terminations are part of the lead frame and the semiconductor moulded in the resin with the lead surface just protruding or flush with the mould compound.
They are produced in plastic (most commonly) and ceramic packages for hybrid and specialist applications. The IPC is currently finalising a document to cover all aspects of this type of component type and is called, ‘IPC-7093 Design and Assembly Process Implementation for Bottom Termination SMT Components’.
On some devices the component terminations are often formed as part of a PCB substrate which is fully encapsulated in a high temperature resin system. In this case, the device is most commonly a complete circuit module with a mixture of passive and active parts with low stand-off height. The substrate provides the interconnection of the components which provide the functionality and are held within the resin. Basically they are examples of the modern day hybrid assembly.
The termination array is made up of either square or round resist defined pads and plated with a nickel gold surface finish. The pads allow direct reflow soldering after placement on to solder paste which has been printed on to the substrate.
As no stand-off is provided on these components the control of the paste thickness and the placement force is critical to the assembly process.
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