How important is the effect of humidity on PCBA?

PCB due to its precision and rigor, the environmental health requirements of every PCB workshop are very high, and some workshops are even exposed to “yellow light” all day long. Humidity, is also one of the indicators that need to be strictly controlled, today we will talk about the impact of humidity on PCBA.

The important “humidity”

Humidity is a very critical and strictly controlled indicator in the manufacturing process. Low humidity may result in dryness, increased ESD, increased dust levels, more easily clogging of template openings, and increased template wear. Practice has proved that low humidity will directly affect and reduce production capacity. Too high will cause the material to absorb moisture, resulting in delamination, popcorn effects, and solder balls. Moisture also reduces the TG value of the material and increases the dynamic warping during reflow welding.

Introduction to surface moisture

Almost all solid surfaces (such as metal, glass, ceramics, silicon, etc.) have a wet water-absorbing layer (single or multi-molecular layer) that becomes visible when the surface temperature equals the dew point temperature of the surrounding air (depending on temperature, humidity, and air pressure). The friction between metal and metal increases with the decrease of humidity, and at relative humidity of 20%RH and below, the friction is 1.5 times higher than at relative humidity of 80% RH.

Porous or moisture absorbing surfaces (epoxy resins, plastics, fluxes, etc.) tend to absorb these absorbent layers, and even when the surface temperature is below the dew point (condensation), the absorbent layer containing water is not visible on the surface of the material.

It is the water in the single-molecule absorbent layers on these surfaces that permeates into the plastic encapsulation device (MSD), and when the single-molecule absorbent layers approach 20 layers in thickness, the moisture absorbed by these single-molecule absorbent layers ultimately causes the popcorn effect during reflow soldering.

Influence of humidity during manufacturing

Humidity has many effects on production and manufacturing. In general, humidity is invisible (except for increased weight), but the consequences are pores, voids, solder spatter, solder balls, and bottom-fill voids.

In any process, the control of moisture and humidity is very important, if the appearance of the body surface is abnormal, the finished product is not qualified. Therefore, the usual work workshop should ensure that the moisture and humidity of the substrate surface are properly controlled to ensure that the environmental indicators in the production process of the finished product are within the specified range.