With the increasing demands for wearable and Internet of Things (IoT) devices, chipmakers are scrambling to yet pack even more circuitry into even smaller component packaging. The micro ball-grid array (BGA) package is a case in point.
Fig. 1 shows micro BGA-packaged devices placed on a flex circuit for a medical electronics application. These tiny micro BGAs can house such complex circuitry as powerful processor chips or a system-on-a chip (SoC), for example.
Typical BGA packages have ball-to-ball spacing of 1.0mm or 0.8mm, whereas typical micro BGA packages have a pitch of about 0.4mm or less. This permits package size reduction, among other advantages, plus micro BGAs can be placed in close proximity on a flex circuit for wearable/IoT applications.
Here are some guidelines and tips to follow to assure efficient PCB layout with micro BGAs.
- Before finalizing a design, the designer should carefully analyze the micro BGA device’s details. He or she should make sure the balls’ pin pitch allows for all traces fanout/routing without using unnecessary special manufacturing requirements and can be done within the allowed number of layers.
- It’s not appropriate to have a traditional dog-bone fan-out pattern for a micro BGA because of its narrow pitch. This means either via in pad or blind/buried vias are used.
- However, to make a micro BGA design cost effective for fabrication, it is better to avoid blind/buried vias, but it really depends on the micro BGA size and its pins assignment.
- The basic and most efficient way of using decoupling capacitors is to place them on the opposite side of the PCB with respect to the micro BGA device and within the grid of vias and contacts used to route signal traces to the micro BGA device.
- Due to the small micro BGA package size, it’s not possible to use 0201 or bigger capacitor packages directly underneath the device. Either a 1005 or smaller package (if available) can be used.
- It is always recommended that while designing PCB layout, all the parts around the BGA should have 20 to 25mm clearance. This space facilitates the re-workability of the micro BGA with out damaging any other parts.
Use of micro BGA packages increases the level of design complexity. The package’s narrow pitch creates a challenge for the PCB layout as do the greater number of pins connecting to the design in a smaller area compared to a conventional BGA. Similarly, board fabrication may be required to undergo advanced techniques, resulting in cost increases. Fabrication facilities need to develop easier manufacture solutions for such finest components and should be prepared for further finest pitch components.