What’s the cheapest package that will work?

By Javier DeLaCruz,
So often, I come across questions from customers asking what’s the lowest cost package technology that will work. The package by itself should not be the singular focus when considering the lowest-cost solution for a new ASIC. The best approach is to take a few steps back and consider the system and what would work best for that given system, from a variety of standpoints such as routability, thermal, signal integrity, etc.

Let’s take an example of a basic WiFi-enabled ASIC. What is the lowest-cost solution? Well, it depends upon what it is going into. If the part is going into a handheld device such as a smart phone, then the lowest-cost solution would likely be a WLCSP (wafer-level chip-scale-package), which is much like a bumped die without a package. Given that the PCBs (printed circuit boards) used by smart phones can handle this smaller bump pitch and trace/space geometry, this makes a lot of sense. On the other hand, if this was going into a home Internet router, a WLCSP would be enormously expensive since it would require utilizing PCB design rules that are uncommon for these larger PCB’s found in typical home routers. It would end up making the system cost go up as the PCB required to route the WLCSP would be likely cost several dollars more. Instead, going to a larger conventional TFBGA with something like 0.8mm or 1.0mm ball pitch makes sense. This is a clear example of how a more expensive package is a better-cost solution.

There are many tradeoffs to be made. The previous example is based on exit routing rules. Let’s consider an example of thermal and signal integrity considerations on a processor-type device. When making the tradeoffs between a thermally enhanced PBGA (HSBGA) or a flipchip BGA (FCBGA), the HSBGA may be less expensive from a packaging cost standpoint. They may both work thermally and electrically, and the HSBGA may be less expensive, so that may appear as the more logical choice, right? Maybe not! With a deeper analysis, you may find that the more expensive FCBGA is a more prudent solution. The FCBGA will likely end up consuming less of the signal integrity budget (reflection and loss) and would also be considerably more thermally efficient then a HSBGA. This may end up requiring a less expensive PCB and a smaller heatsink. It may also require less airflow or none at all.

Please make sure to consider the cost of the system above all else. The cost of the individual component may not be nearly as relevant. Having all of the resources available to make decisions at multiple levels upfront is paramount. If you do not have these resources easily available, finding a partner that can bring these vantage points to the table will work to your advantage.

–Javier DeLaCruz is eSilicon’s Semiconductor Packaging Director