Take a look at the chart below to see where your OEM designs will likely be trending over the next few years, if you’re not there already.
Newer and newer PCB technologies are steadily coming into being and package-on-package (PoP) is among the latest gracing our boards. Actually, PoP isn’t that new for a number of early adopter OEMs. But the technology that is new is 0.4mm ultra-fine pitch BGAs used on the next round of PoP technology.
It’s important for you to know at this juncture that design rules for 0.5mm pitch BGAs don’t play well at the 0.4mm ultra-fine pitch BGA PoP level. In this case, you have to rely on the experience and know how your PCB designers have stored up over their years of designing boards. The reason is there are no standard design rules yet for PCB designs based on 0.4mm ultra-fine pitch BGA PoPs.
Check out our recent article in PCD&F Magazine about Stepping Out With 0.4mm Pitch BGA/PoPs
In the meantime, there are some basic guidelines and tips thatíll help you to better understand these new PCB design trends.
- Know that solder-mask defined or SMD is the pad of choice for 0.4mm ultra-fine pitch BGAs.
- Don’t let your PCB design house try to sell you on using traditional BGA dog-bone fan-out. Instead, via in pad is more effective for escape routing fine pitch BGAs.
- Vias placed on BGA pads should be filled with non-conductive material. The reason is they perform better because coefficient of thermal expansion is comparable with that of the PCB.
- When there are vias below a BGA, other vias available for connection should be filled, tented, or capped. Otherwise, they can cause voids and out-gassing during reflow.
- Specifically, at the 0.4mm ultra-fine pitch level, BGA/PoPs should be placed offset from each other with about 500 mil spacing to maintain board level reliability and ease of debugging on the bench when needed.
- Again, at 0.4mm ultra-fine pitch, it’s best not to use an auto router, but rather perform manual routing. Otherwise, unusual traces and many unnecessary vias being routed can result.
There’s always talk about working together to successfully complete a project. But in the case of 0.4 mm ultra-fine pitch BGA/PoP-based PCBs, there is no question about it. It is essential and paramount that the PCB designer, fab shop, and assembly engineering work in unison with the PCB designer taking the lead. Otherwise, the slightest error or misunderstanding can prove extremely costly.