Baking circuit boards prior to assembly

Every effort is made to minimise the moisture content in the finished PCBs supplied by Momentum Circuits.

All of our circuit boards are supplied in vacuum packaging with a choice to include silica desiccant and humidity indicator strips.

Despite these safeguards, it is recommended to pre-bake circuit boards of high layer count, boards being populated with a high value of components and without exception any boards with flexi or flexi-rigid technology.

Momentum Circuits recommend that boards made with flexible materials are baked prior to exposure to solder processes (e.g. solder leveling and reflow). Boards are generally baked at 250  F (121  C) for two to ten hours **, depending on the board thickness and design.

Baking removes any moisture that may have been absorbed during processing. Polyimide films absorb moisture quickly; therefore, soldering and reflow should be done within 30 minutes after baking.

Vacuum ovens are also used to remove water. Lower temperatures, such as 150-175  F (65-80  C) can be used. This method also reduces the oxidation of the exposed copper pads.

Boards should be baked prior to soldering by hand, wave, IR and Vapor Phase soldering. This bake is typically done at 250  F (121  C) for two to ten hours, depending on the board thickness and design.

Moisture Absorption 

Kapton® HN: 2.8%
Pyralux® LF: 2.8%
Pyralux® FR: 2.8%
Pyralux® AP: 0.8%
Pyralux® AC: 0.94%
 
** Times may vary based on the following items:
-  Size of the board
-  Number of layers in the board
-  Amount of copper ground planes or stiffeners (if there are large copper 
ground planes (or stiffeners), the moisture can only escape in the x-y 
direction, taking longer to do so).
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