Micro BGAs are proving exceedingly popular these days. These small packages are not only populating conventional PCBs that continue to increase in complexity, but also the smaller circuit boards for IoT and wearable devices.
The micro BGA package is more compact than other SMT devices and hence, has a shorter contact length from the device pin to the outside world. Therefore, it provides a lower inductance/impedance path to all signals. It can keep pace with the advance of IC semiconductor and logic implementation technologies. It also minimizes signal losses by increasing the packaging density and reducing the packaging delay.
However, micro BGAs pose a significant challenge for PCB design. A typical micro BGA features 0.4 mm pitch. But there are growing numbers of finer pitch micro BGAs at 0.3 mm and even 0.25 mm pitch being placed on PCBs. PCB layout engineers must first find easier ways for pins fanout/routing solutions for 0.4mm pitch BGA. Otherwise, routing complications can result. Consequently, those complications cause an increase in layer count and sometimes call for high-end fabrication requirements.
For a more detailed account of designing with micro BGAs, check out our article.
In the meantime, here are some tips and hints of what to know when your upcoming product designs call for micro BGAs.
- One key thing to know is there are normally two types of land patterns used for micro BGA pads – NSMD (non solder mask defined pads) and SMD (solder mask defined pads). Fig. 1 shows the difference.
- Traditional dog-bone fan-out pattern is not appropriate for a micro BGA due to its narrow pitch. Either via in pad or blind/buried vias are used.
- The designer can fan-out/route all micro BGA pins with a regular 6 mil via size in a minimum number of layers and without using high-end fabrication techniques.
- The most efficient way to use 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 contact used to route signal traces to the micro BGA device.
- It’s not possible to use 0201 or bigger capacitor packages directly underneath the device due to the small 0.4mm pitch micro BGA package size. Either a 01005 or smaller package is recommended.
- During PCB layout, it’s recommended that all parts around the micro BGA should have 20 to 25mm clearance facilitating re-work of the micro BGA without damaging nearby components.
A micro BGA offers a number of electrical and physical benefits. However, a micro BGA is not without problems. For example, rework methods are more difficult; solder joint reliability is more critical, voiding becomes an increasingly critical issue and micro BGA assembly inspection is more difficult. But those issues can be minimized or eliminated by working with an experienced EMS provider offering you both PCB design and assembly.