What is PCB Baking?

What is PCB Baking? Why do we need to do it?

PCB Basics 
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Editorial Team - PCB Directory

Sep 27, 2020

PCB baking is a way to remove moisture from a fabricated PCB. When the surface of a PCB is cooler than the air that surrounds it, condensation can occur. This results in moisture getting trapped in the printed circuit board or getting absorbed by the laminate material of the PCB. If there is moisture left in the PCB, it can turn into water vapor/steam in various PCB processing stages and expand,  which can damage the board or result in circuit failure. The amount of moisture content that a PCB will absorb depends on the laminate material used in the PCB. For example, polyimide flex and rigid materials can absorb more moisture than FR4 boards.

In the PCB Baking process, the PCB is placed in an oven which is usually maintained at a temperature from 100 to 110 °C (Can go up to 130 °C). The high temperature results in the evaporation of moisture from the board. It is important not to overheat the board or bake it for too long as this can result in damaging the board. Weight gain and loss measurements can be used to determine if the moisture has evaporated from the circuit board.

One of the main objectives of PCB baking is to eliminate outgassing of moisture through the copper plating in via holes and prevent delamination or measling of the PCB. Outgassing in via holes occurs during the automated or manual soldering process causing blow holes or sunken solder fillets, pin holes. Delamination or measling can occur when moisture accumulates in voids or at the interface between the epoxy/laminate on poorly bonded multi-layer boards, during the rework or solder process.

Do we need to bake all printed circuit boards?

PCB Baking is not always required. It is better to prevent moisture from entering the board itself. This can be done at the very beginning of the PCB design and manufacturing process. The design of the PCB decides whether moisture is more or less likely to be an issue. The lamination process of the PCBs is supposed to be conducted in a temperature-controlled environment. This step is usually enough to dehydrate the board. Moreover, the material of a PCB also plays a vital role in moisture absorption, material which are hygroscopic. FR4 as a PCB is base tends to delaminate due to solder reflow, because it is hygroscopic. On the other hand, there is material like polyamide, used in flex or rigid-flex PCBs, they are unaffected by baking. They are prone to expansion and their solderability gets effected in the process often, but baking does not help these sorts of PCBs. In today’s PCB materials the epoxy to laminate adhesion has increased to a level that baking is an unnecessary step addition.

It is important to know the materials, quality of circuit manufacture, surface preparation, and all other aspects of your circuit board before you jump to baking. But having said so, baking is a very good way of getting rid of any sorts of moisture or solvents (if any) in a PCB. It is also a good way to expand a PCBs life-span.

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