In previous postings, you have heard about using mezzanine connectors to enhance system level flexibility and provide a variety of options for IO configurations. This approach can cost effectively increase the size of the available market for your product as well as substantially increase the useful life of the base board. Mezzanine solutions can solve many other system level problems as well.
Reduce system cost by isolating complexity
Printed circuit boards are a significant piece of total system cost, especially in systems that pack lots of function onto one PCB. Examples cross many applications:
• Large FPGAs (Field Programmable Gate Arrays) are the heart of many systems. These chips require many pins to provide the IO, power, and multitude of ground connections needed to support signal integrity needs for high-density interconnection. The more rows in the pin field underneath the device, the more PCB layers are necessary for routing out of the pin field. With a very tight 1 x 1-mm grid, generally only one trace can be routed between vias under the FPGA. The more pins, the more layers are needed.
• These traces need to be fine, with 0.004 in. being a typical trace width. To keep the PCB thin as layer counts increase, traces need to be as narrow as possible. Boards with fine features and many layers are expensive to make and, as the board becomes larger, the board becomes geometrically more expensive because of lower yields.
Along come mezzanine boards to save the day
Instead of having a full motherboard that is complex, it is quite possible to have an “island of complexity” in the middle of a lower technology board. The PCB right under the FPGA is commonly 2x the FPGA dimension both ways and can be precisely back drilled for maximum performance. This allows the traces to fan out to an interconnect area that can use conventional mezzanine connectors. The motherboard can then become less complex, having fewer layers, larger vias, and much lower manufacturing cost. This technique is commonly used across a wide range of systems.
These islands of complexity can also include boards with blind and buried vias or other features not suitable for large format motherboards.
Some devices require boards with special technology for optimum performance. For example, because RF boards are optimized for very precise impedance control, low crosstalk, and minimum loss, you will often want to use Teflon PTFE inner layers. It is a significant cost benefit if this technology can be confined to a mezzanine card. Fiber transceivers are another technology that can benefit from being on a small, readily replaceable card.
As a result, mezzanine boards can also serve as a bridge between the nanometer scale technology used on semiconductors and the 1- x 1-mm scale interconnects used for FPGA to PCB connections and the more robust PCB and connector technology used on plug-in cards or motherboards used in larger systems.
Improving time to market for new chips
How many times have you had to delay development of a next generation system because a new chip is not yet available? Mezzanines can enable developers to bring up and debug the system with existing semiconductors, then quickly drop in the latest and greatest when it becomes available, mitigating risk, improving time-to-market, and creating a much smoother transition between systems shipping today and upgrades for tomorrow.
This approach can also allow a manufacturer to develop the system with two alternative suppliers. If a common mezzanine format is chosen, semiconductor suppliers will compete based upon function, availability, price, and quality. The successful suppler will be the first to deliver all four attributes.
Some parts have inherently lower yields. By placing these parts on a mezzanine, system fabricators and integrators can quickly make a last minute repair, if necessary, by just replacing the mezzanine cards, improving on-time shipments, quality and yields. The fiber example above can fall into this category.
Mezzanine connectors have been the work horse of the connector industry for a couple of decades, adding lots of system level flexibility and the ability for OEMs to quickly and easily customize their offerings for their customers. Mezzanines also help to control costs by partitioning complexity or special technology components from the base boards. When properly used, mezzanines can reduce your cost and risk while improving your responsiveness to your customer.
People seldom think about connectors reducing system cost and improving quality, but as you can see, they certainly do.