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Rebuilding the Foundation: Base Material Damage

You're holding a board with base material damage - the board is beyond repair, right? Think again.

All too often, valuable circuit boards are scrapped due to base material damage. Actually, boards with base material damage can be reliably repaired. Now that some large panel circuit boards are exceeding 30-inch dimensions, may be up to a half-inch thick, weigh 30 to 50 pounds, and be worth up to $20,000 to $30,000 - the importance of knowing how to repair base material damage, rather than scrapping the board, may indeed make a significant impact on a company's bottom line.

A number of well established procedures exist for reliably repairing base material damage stemming from a variety of causes. Damage can include chipping, burns from overheated components and misoriented capacitors. Damage may occur during rework, such as delamination and measling caused by overheating the board with a soldering iron or a hot air tool, or may result from board design errors, requiring the relocation of a tooling hole or alignment slot.

Following are three of the major, or most frequently encountered, base material damage repair methods.

Figure 1: Typical corner damage that can be repaired using a transplant method.

Base Material Repair, Edge Transplant Method
When circuit board damage occurs at the corner, or along the edge of a board, new base material is often transplanted to the damaged area. The transplant process is normally completed with a tongue and groove joint method. This method is a bit more complicated if inner circuitry has been damaged. In those cases surface wires may be required to restore electrical connection. The procedure involves cutting a fresh piece of board material the same thickness and type as the piece removed.

A tongue and groove joint is used for greater support of the replacement piece being added to the section of the original circuit board. The mating surface of the joining area is coated with a two-part epoxy to secure the new piece in place. After the epoxy is fully cured, the area is cleaned of any excess epoxy, then milled or cut to meet the original dimensional design requirements. See Base Material Repair, Edge Transplant Method for a detailed step-by-step procedure. (See Figure 1).

Figure 2: Typical minor base board damage repaired with epoxy.

Base Board Repair, Epoxy Method
Often, removing the damaged area and filling with high strength epoxy can correct minor base material damage. Coloring agents can be added to the epoxy to blend the repaired location with the original solder mask. The repair method is actually more than cosmetic - repairing the burn or hole prevents moisture and other agents from eventually working their way into the board laminate and causing problems.

This method also restores strength to the area. Burned or frayed material is abraded away with a ball mill, or other appropriate tool, to create a fresh surface on which the high strength epoxy can adhere. After the epoxy has cured, the excess is removed to make the new area planar to the surrounding area. See Base Material Repair, Epoxy Method for a detailed step-by-step procedure. (See Figure 2).

Figure 3: Typical minor key slot damage that can be repaired with epoxy.

Key and Slot Repair
The key and slot repair method is used to repair minor damage to a key slot or other cutouts in a printed board or assembly. Key slots or cutouts can be repaired by cleaning/abrading the damaged area and filling with epoxy, then milling the epoxy to smooth the dimensions to their original shape. See Key and Slot Repair, Epoxy Method for a detailed step-by-step procedure.

At other times, a piece of material must be fitted in a tongue and groove manner, whereby a replacement piece of matching board material is epoxied into the area needing repair. A new cut is then machined into the repaired area if needed. 

Several members of the Circuit Technology Center team contributed to this feature story.