This invention relates in general to printed circuit boards (xe2x80x9cPCBsxe2x80x9d). More particularly this invention relates to a PCB assembly that can be economically and reliably reworked.
A person who designs and builds a PCB does not normally intend for the PCB to be reworked. PCBs often do need to be reworked, however. This need for reworking can be due to PCB layout errors, incorrect component selection, a change in design parameters, or any number of reasons. As is well known, reworking PCBs, especially PCBs with surface mount components, is difficult.
One conventional method to rework a PCB involves bonding rework wires to component leads. This task is labor intensive, especially with surface mount components. In addition, proper bonds between component leads and rework wires are difficult to achieve. Further, during the bonding process, the component may be damaged.
Another conventional method to rework a PCB involves scraping off the soldermask from PCB traces and/or PCB vias and attaching a rework wire to the exposed metal. In addition to being labor intensive, such methods often create surface imperfections in the exposed traces and/or vias. The surface imperfections, under certain environmental conditions such as shock, vibration, and/or temperature fluctuations, can fatigue and cause failures.
The invention relates to a PCB assembly which allows economical and reliable rework. The PCB assembly contains a soldermask and a trace with a portion of the trace exposed by a soldermask relief. When the PCB assembly requires rework, a rework wire is bonded, using conventional intermetalic bonding materials, to the portion of the trace exposed by the soldermask relief. There is no need to bond a rework wire to a component. Further, there is no need to scrape off the soldermask and possibly damage the traces and/or vias. The bonds are high reliability bonds, and the labor required to perform such bonds are minimal.