Posts Tagged ‘SMT PCB assembly’

Mirror Mirror

Written by Admin on . Posted in PCB Assembly and component

A mirror can bring bad luck, it is said. In this PCB assembly challenge, it certainly did when a mirrored pad layout for a transformer made it impossible to mount the component to its intended location on the top side of a PCB in its usual orientation.

Design error: A mirrored pad layout creates orientation problems between pads and component pins; layout is for bottom-side rather than top-side mounting.

Design error: A mirrored pad layout creates orientation problems between pads and component pins; layout is for bottom-side rather than top-side mounting.

 

The component’s footprint, it turns out, would work fine if it were on the opposite side of the PCB, but that bottom-side installation is not possible.

Flipped upside down, the SMT transformer’s pins line up fine, except that they are facing upwards. But we can still mount the component and make a robust connection using adhesive and connecting wires.

Flipped upside down, the SMT transformer’s pins line up fine, except that they are facing upwards. But we can still mount the component and make a robust connection using adhesive and connecting wires.

 

The customer made a design mistake; although the pads for top-side SMT mounting of the component are in place, they are in mirror-image orientation; e.g., the pad layout with Pin 1 is intended to be installed from the bottom of the board. Consequently, it doesn’t match up in terms of orientation on the top side of the PCB unless the component is literally placed onto its back. But that means that the leads are sticking up into the air, pointing in the wrong direction.

 

Small dots of epoxy are applied to the PCB surface and to the component body, before it is attached, the epoxy cured, and the transformer connected pin by pin.

Small dots of epoxy are applied to the PCB surface and to the component body, before it is attached, the epoxy cured, and the transformer connected pin by pin.

 

It’s well known that a dab of epoxy can cure a host of ills, and in this case it was simply a matter of dispensing a tiny amount of epoxy onto the back of the component body, in the center, as well as onto its intended location on the SMT PCB assembly.

The component is then carefully located in place upside-down and the epoxy cured. With the component robustly mounted in this manner, small wires were then run from each lead (pin) to its corresponding pad on the board’s surface.

 

It requires skillful hand soldering once the component is in place, but the connection is robust and complete.

It requires skillful hand soldering once the component is in place, but the connection is robust and complete.