Circuit Technology Center
 
No. 2.7
Epoxy Mixing and Handling

OUTLINE

This procedure covers epoxy mixing and handling. The epoxy covered by this procedure has multiple uses including solder mask repair, base board repair, circuitry over-coating and delamination repair.

NOTE
For high strength or high temperature applications two part epoxies will generally have the best properties.
 
PROCEDURE REFERENCE
CTC  7721 1.0 Foreword
CTC  7721 2.1 Handling Electronic Assemblies
CTC  7721 2.2 Cleaning
CTC  7721 2.5 Baking and Preheating
IPC 7721 2.7 Epoxy Mixing and Handling

TOOLS & MATERIALS
Cleaner
Color Agents
Epoxy
Foam Swabs
Heat Lamp
Mixing Cups
Mixing Sticks
Oven
Wipes

Epoxy Specifications
The Epoxy used at Circuit Technology Center facilities has the following properties.

Packaging   -   2 gram prepackaged containers
Color   -   Clear, transparent
Pot life   -   30 minutes
Cure cycle   -   24 hours at room temperature or 1 hour @ 165°F (74°C)
Viscosity (after mixing)   -   1900 cps @ 77°F (25°C)
Operating temperature range   -   76°F to 284°F (-60°C to 140°C)
Hardness   -   88 Shore D
Dielectric strength   -   410 volts/mil

PC BOARD PREPARATION
The area where the epoxy is to be applied should be prepared prior to mixing the epoxy. This preparation may include preheating the affected area to improve absorption of the applied epoxy. The entirecircuit board may also be heated in an oven or with a heat lamp.

CAUTION
Some components may be sensitive to high temperatures.

PROCEDURE - Prepackaged Two Part Epoxy

  1. Remove the clip separating the resin and hardener. Mix by squeezing both halves together with your fingers. Mix for at least one minute to ensure a complete mix of the resin and activator. (See Figure 1).


  2. Cut open one end of the epoxy tube and squeeze the contents into a mixing cup. Mix again with a mixing stick to ensure a thorough mixture of the resin and hardener.


    3. NOTE
    For bubble free epoxy, remove the clip separating the resin and hardener. Cut open one end of the Epoxy tube and squeeze the contents into a mixing cup. Slowly stir the mixture with the mixing stick. Be sure to stir the mixture for at least 2 minutes to ensure that all the resin and hardener have completely mixed.

  3. If needed, add color agent to the mixed epoxy. Stir slowly to prevent bubbles.


  4. Apply or use as needed. (See Figure 2)


  5. Cure the epoxy for 24 hours at room temperature or 1 hour @ 165°F (74°C)

EVALUATION

  1. Visual examination of epoxy for texture and color match.


  2. Testing of epoxy surface for complete cure.


  3. Electrical tests as applicable.
 		  
Solutions Across the Board TM

Product Class:  R/F/W/C
Skill Level:  Intermediate
Conformance Level:  High
Revision:  D
Revision Date:  Jul 7, 2000 
Repair Service Charge

  
Figure 1: For prepackaged epoxy, remove divider clip and mix resin and hardener inside package.
  
Figure 2: Apply epoxy as needed. Foam swabs may be used to add texture for soldermask repair.
Tricks of the Trade
 You can't beat using Pre-packaged Epoxy for most circuit board repair and rework applications. Two part epoxy will give you the mechanical strength and dielectric insulation that most one part epoxies simply can not. Curing in an oven will enhance the epoxy properties.
 
 
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