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2.5 Baking and Preheating

Outline
This procedure covers baking and preheating of printed boards and printed board assemblies to prepare the product for the subsequent operations. Included are steps for:
  1. Baking
    Baking is used to eliminate absorbed moisture. Whenever possible circuit boards and circuit Board assemblies should be baked prior to soldering, unsoldering and coating operation to prevent blistering, measling or other laminate degradation.
  2. Preheating
    Preheating is used to promote the adhesion of subsequent materials to the board surfaces and to raise the temperature of the circuit board to allow soldering and unsoldering operations to be completed more quickly.
  3. Auxiliary Heating
    Auxiliary heating is the addition of a second source of heat. This can be from a hot air tool, or from a second soldering station. A common application is to provide additional heat when removing through hole components that may have connections to internal power or ground planes.
  4. Thermal Profiles
    Ball Grid Array, Chip Scale Packages, and Flip Chip Packages may require the development of "Time Temperature Profiles" to remove or install these devices.
Caution
Baking and preheating procedures must be carefully selected to ensure that temperature and time cycles used do not degrade the product. Environmental conditions must also be carefully considered to ensure that vapors, gases, etc., generated during the heating process do not contaminate the product's surfaces.

Caution
Some manufacturers of ceramic chip capacitors recommend that the Preheat Ramp Rate not exceed 2-4 degrees C/Sec.

Caution
To prevent fluxes or other contaminates from being baked onto the board surface, thoroughly clean the board or assembly prior to baking or preheating.

Minimum Skill Level - Intermediate
Recommended for technicians with skills in basic soldering and component rework, but may be inexperienced in general repair/rework procedures.

Conformance Level - High
This procedure most closely duplicates the physical characteristics of the original, and most probably complies with all the functional, environmental and serviceability factors.

Procedure References
1.0 Foreword
2.1 Handling Electronic Assemblies
2.2 Cleaning
IPC7721 2.5 Baking and Preheating
Tools and Materials
Procedure for reference only.
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