Many terms tend to mixed together when people are discussing PCB repair. The resource for terms in electronics assembly can be found in the IPC T-50 which lists the terms and definitions for electronic assemblies. Touch up, rework and repair often get intermingled. “Touch up” is done in the assembly process when alleged defects are identified and a heat source is brought onto the product in order to eliminate the defect. “Rework” refers to the action of re-processing a non-compliant product through the use of original or equivalent processing in a way which insures that the original applicable drawings or specifications are in compliance. For example, if post conformal coating the PCB has an area which should have had conformal coating but doesn’t, coating material can be applied to that area as a rework operation. The final coated board is required to be in compliance with the original coating specification. The “repair” of a product is an action in which a nonconforming product is restored to the functional capability. However, in the case of repair it does not assure compliance of the article with the original drawings or specifications.
As this definition of repair indicates the final product will not look like the original unit as signs of some of the repair work done will be visible. An example of this would be a burned hole in a board which has been fixed by removing the burned area and refilling it with epoxy. This will be visible and this is considered a repair process and it has to be be approved by the customer.
Listed below are the most common PCB repairs:
PCB land lifting/replacement
A PCB land is considered “lifted” off the board and is a defect per the IPC-A-610 inspection standards when it is pulled away from the PCB at least one thickness of the land. For a 1 ounce copper land the thickness is specified to be 1.4 mils (35 um) and therefore any “peeling” up of the land beyond this thickness would be considered a defect and can be repaired. This defect can occur when force, usually under temperature, is applied to the pad during device removal. In other cases there may be board handling damage which causes the pad to be lifted.
The repair of a lifted land can be accomplished via a variety of methods, but the IPC 7711/21 Rework, Modification and Repair of Electronic Assemblies defines two specific processes in the repair standard. One involves the use of epoxy to re-bond the lifted pad. Liquid epoxy is inserted under and around the lifted pad in order to re-attach it to the PCB. In the second method an epoxy film is used to bond the two materials back together. After placement of the dry film epoxy between the board and the pad, heat and pressure is applied to activate the adhesive an facilitate the repair.
The other variation on this type of SMT repair is that a conductor or trace is lifted or has been completely removed from the PCB.
PCB laminate damage
One of the next most common SMT repairs which occurs is damage to the laminate. Laminate damage occurs when there is improper board handling by personnel or when the protective packaging is not adequately applied to protect the PCB. There are a variety of methods which can be used to make this repair including an epoxy and a transplant method. In the epoxy method a temporary mold is created and epoxy is filled into the mold. After curing the epoxy is sanded to size and fit. In the replacement method a board of similar thickness and characteristics is “fitted” into the broken area.
This is normally done when the damage is extensive and PCB assembly has enough value to warrant the repair time.
Another common physical damage to the PCB requiring repair is solder mask damage. This generally occurs when there is improper board handling, improper packaging and protection or during the PCB rework process. Solder mask can be repaired when replacement solder mask is dipped, brushed or sprayed onto the PCB subject to proper area definition via masking.
While there are many other PCB repairs, those listed above are the most commonly observed. PCB repair can be accomplished on almost any PCB assembly, the only question is how much repair labor will be involved.