When two printed circuit boards are mated together within a vehicle, a number of elements under the hood can impact the connection.

Shock, thermal variation, or vibrations, for example, can all lead to stress on the solder joint and ultimately lead to failure.

OEMs are increasingly turning to an option that "floats," according to Matt McWhinney, Business Development Manager at the Illinois-based interconnect manufacturer Molex.

A "floating" connection enables boards to move relative to each other. Placed on a springform bed, the connectors move as much as a millimeter in the x, y, or z axis.

Compared to an ordinary connector where alignment must be perfect, the "floating" boards have more give and flexibility between the contacts during mating.

Board-to-board setups are also often more expensive than stretchy alternatives like flexible fiber cable (FFCs) and flexible printed circuits (FFCs), but McWhinney says manufacturers are willing to pay up for increased reliability.

Matt McWhinney, Business Development Manager, Molex

"This is why almost always when two PCB are mated together, designers are turning to these types of connectors," said McWhinney in a live Tech Briefs presentation this month.

Two attendees had questions about floating connectors. Read McWhinney's edited responses below.

Which is better: FFC/FPC connectors or board-to-boards? When should one be used, and when should the other be used?

Matt McWhinney: It really depends on the architecture. If you think about it, mechanically: How's the layout? What are you trying to connect?

Board-to-board can be used in what's called a "mezzanine connection." The boards are parallel to each other. That certainly is an appropriate option. "Board-to-boards" can also be used where one half of the board is soldered to the printed circuit board, and the other half is soldered to an FPC cable. If you need to mate or join a board together to a board, or a board to a component, such as a display, often another approach would be an FFC or FPC connector, where there's a flexible connector in between them.

It's really a matter of design philosophy. Some design shops or engineering teams really prefer one over the other. Or some could just be appropriate to the fit, form, and function.

Also, FPC connectors have a locking system in then. Board-to-board connectors typically don't, so if you have a high-vibration environment, either the boards would need to be secured together or they would require a secondary lock, like foam or tape.

Why do I need floating board to board connectors vs. regular board-to-board connectors?

Matt McWhinney: Floating board to board connectors are especially appropriate for a mezzanine type connection, where you're joining two printed circuit boards together. And basically it's to reduce stress on the solder joint.

So, if you have a camera system or an ADAS system that's potentially keeping people alive or keeping them in the right place on the road, and that vehicle is designed to operate for 10 years, that's 10 years of abuse on those boards: shock and vibration and thermal expansion and contraction.

Floating helps to ensure that the connection will survive [those factors] long-term. A floating component may not be needed if it was a board-to-board that was connected with FPC cable, and that cable was maybe taped down where there wasn't a mass of vibration taking place between the boards.

It's the way that automotive designers are going.

Share your own questions below.