Electronic Design

Mounting Power Converters On Printed-Circuit Boards With Sockets

High-value pc boards, used in mainframe computers, automatic test equipment, industrial control systems, and telecommunications systems, frequently incorporate single or multiple ac-dc or dc-dc converters, power supplies, and battery packs. During assembly, conventional approaches to mounting the converters involve soldering them to the pc board using wave or reflow techniques. However, power converters can be relatively bulky with considerable thermal mass, causing them to act like large heatsinks.

Therefore, board makers must compensate by extending thermal exposure times to complete the soldering operation. This lengthens production cycles, boosts energy usage, and drives up board-assembly costs. Moreover, if boards with conventional soldered-on converters fail in the field, repair is often time-consuming and costly.

On the other hand, if designers specify sockets for mounting these large devices, they can simplify assembly, shorten production time, cut energy costs, and facilitate field rework and repair operations. For example, Advanced Interconnections has employed a peel-away socket carrier to alleviate the above converter mounting problems (see the figure). This approach also works well for mounting other large and/or heat-sensitive components such as battery packs.

Each socket carrier consists of a flexible yet stable, transparent polyimide carrier film that incorporates an array of low-profile (0.15-in. \[0.38-mm\] installed) socket terminals. These terminals match the footprint and pin pattern of the converter to be mounted. Screw-machined terminals with beryllium copper contacts can handle the heavy amperage requirements of the power-conversion devices.

The socket carrier aligns precisely to the board's mating surface every time. It also ensures that all sockets are vertical to the plane of the board before soldering to allow for proper insertion of the converter's contact pins. Because it has only a fraction of the thermal mass of the power converter, the socket carrier can be soldered more quickly and economically by wave or oven reflow. Another advantage is that the socket carrier lets multiple sockets be installed faster and more easily than individual loose sockets, which must be positioned and soldered individually.

Once the terminals are installed on the circuit board, the converter mounts quickly and securely without soldering by pressing its contact pins into the terminals. If a converter ever needs field replacement, the failed unit can simply be withdrawn from the socket and a replacement plugged in. This minimizes system downtime, safeguards the circuit board from damage during repair, and reduces the need to stock costly spare boards.

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