2.5 Baking and Preheating

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 °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.