As the demand for compact, lightweight, and high-performance products grows, innovative techniques like directly soldering bare chips onto printed circuit boards (PCBs) become essential. This method known as chip on board (COB) for rigid PCBs and chip on flex (COF) for flexible PCBs, addresses these needs effectively.
When direct soldering of bare dies onto a PCB is impractical or not feasible, they are soldered onto an IC substrate, bridging the nanometer-scale world of integrated circuits (ICs) with the micrometer-scale world of PCBs. As substrates and PCBs shrink, designs become denser, requiring advanced materials and manufacturing processes. Space savings can be achieved by combining several chips into multi-chip modules or using chiplets.
The intricate patterns of advanced chips are often too dense to be directly attached to a PCB. IC substrates resolve this issue by providing a dense design that allows the chip to connect on one side and interface with the PCB on the other. To achieve these dense designs, we utilize cutting-edge circuit materials such as Ajinomoto Build-up Film (ABF) and advanced manufacturing techniques like modified Semi-Additive Process (mSAP) and Semi-Additive Process (SAP).
An interposer is a very dense substrate that electrically connects several chips or chiplets on the top side, redistributing the input and output connections of the ICs to match the footprint of the substrate or PCB. Interposers are critical in advanced packaging solutions like 2.5D.
Flexible PCBs, thinner than their rigid counterparts, support complex designs that can bend and fold into various shapes, making cables and connectors unnecessary. Attaching bare dies directly to flexible PCBs significantly enhances performance, design flexibility, and reduces weight and space. After assembly, flexible PCBs can be folded to create components with two or more layers, each containing mounted components.
A recessed area in a cavity PCB allows for the accommodation of bare dies and other components. Using materials such as epoxy, the bare dies can be encapsulated effectively sealing and protecting them while saving space and enhancing performance. Cavity PCBs can be realized with both rigid and rigid-flex configurations, eliminating the need for cables and connectors, thereby increasing reliability and reducing weight and space.
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