Circuit Board Repair and Rework Guide > 3.0 Base Board Procedures > 3.4.1 Key and Slot Repair, Epoxy Method

3.4.1 Key and Slot Repair, Epoxy Method

Printed Board Type: R/W | Skill Level: Advanced | Conformance Level: High | Rev.: D | Rev. Date: Jul 7, 2000

Outline

This method is used to repair minor damage to a key slot, or other cutout in a printed board or assembly. The area is repaired using high strength epoxy.

Caution
Care should be taken to limit the application of epoxy to the specific areas desired and to avoid damage to the conductive patterns, contacts and components.

Acceptability References
IPC-A-610	2.0	Externally Observable Characteristics
IPC-A-600	10.0	Laminate Conditions

Damaged Key Slot

Procedure References
CTC	1.0	Foreword
CTC	2.1	Handling Electronic Assemblies
CTC	2.2.1	Cleaning, Local
CTC	2.2.2	Cleaning, Aqueous Batch Process
CTC	2.5	Baking and Preheating
CTC	2.7	Epoxy Mixing and Handling
IPC7721	3.4.1	Key and Slot Repair, Epoxy Method
Tools and Materials
Ball Mills Base Board Repair Kit Cleaner Color Agents Epoxy Knife		Micro-Drill System Mixing Sticks Oven Scraper Tape, Kapton Wipes

Procedure

Mill away damaged board base material using a Micro-Drill System and ball mill.

Figure 1: Mill away the damaged
board base material using a Micro
Drill System and ball mill.

1.	Clean the area to be filled, including the edges.

2.	Mill away the damaged board base material using a Micro-Drill System and ball mill. All damaged base board material must be removed. No fibers of laminate material should be exposed at the surface of the keyslot. (See Figure 1).

	Note To clearly see that all damaged material has been removed, flood the area with alcohol or solvent. Damaged internal fibers of the base material will show up clearly.

	Caution Abrasion operations can generate electrostatic charges.

3.	Remove all loose material and clean the area.

4.	Apply Kapton tape to the surface of the circuit board adjacent to the slot. The Kapton tape should protect any adjacent contacts or components.

	Note The circuit board may be preheated prior to filling the area with epoxy. A preheated PC Board will allow the epoxy to easily flow and level out. Epoxy applied to an unheated circuit board may settle below the circuit board surface as the epoxy cures.

5.	Mix the epoxy. If desired, add color agent to the mixed epoxy to match the PC board color.

Apply epoxy to edges of key slot using a mixing stick sharpened at end.

Figure 2: Apply epoxy to the edges
of the key slot using a mixing stick sharpened at the end.

6.	Apply a small amount of epoxy to the edges of the slot. A mixing stick sharpened at the end may be used. (See Figure. 2).

	Note A slight overfill of epoxy may be desired to allow for shrinkage when epoxy cures.

	Note The circuit board may be turned on its side to keep the epoxy in place while it cures.

7.	Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.

	Caution Some components may be sensitive to high temperature.

8.	After the epoxy has cured remove the Kapton tape.

9.	If needed use a knife or scraper and scrape off any excess epoxy.

10.	If precision is required, machine the edges of the slot using a milling machine or Precision Drill System and appropriate milling cutter. Use great care to correctly relocate the slot.

	Note If needed, apply additional thin coating to seal any scraped areas.

11.	Clean the area.

Figure 3: Completed key slot repair.

Evaluation

1.	Visual examination and measurement of key slot location and dimension.

Figure 4: Micro-Drill System.