SMT Processing Workshop Temperature and Humidity Management Specifications

One of the key measures to prevent defects in printed circuit boards (PCBs) is to control the factory
environment strictly. Failure to properly manage humidity and temperature in the production area can
cause damage to expensive electronic components, leading to quality issues and unnecessary expenses. The
production environment is affected by many factors, including the factory's location and the type of
equipment used to produce the boards. Even in mild climates worldwide, manufacturers must continuously
monitor and adjust the temperature and relative humidity of the workshop to ensure production quality.

Relative humidity

Humidity is measured based on the "relative humidity" (Rh) in the room, which reflects the
ratio between the partial pressure of water vapor and the saturated water vapor pressure under the same
temperature conditions. In other words, relative humidity is a quantitative analysis of the amount of
water vapor in the air.

High humidity

High humidity in the manufacturing environment can cause many serious problems:

Slippage: welding paste absorbs too much water and causes bridging during reflow.

welding balls (or "popcorn"): Excessive water absorption in the welding paste
causes poor coalescence.

Outgassing: Large amounts of water flow on the surface of surface-mounted devices
(especially BGAs) and can cause pressure increases. In certain cases, this can cause the lid to blow
off.

Low humidity

The rapid evaporation of the flux can cause the welding paste to dry out. This phenomenon can lead to
poor stencil release and welding joint defects.

High temperature

High temperature reduces the viscosity of the welding paste. This can cause various problems: mainly
uneven application and collapse of the welding paste, but it can also cause bridging and welding joint
defects such as voids. In addition, high temperatures can cause excessive oxidation of the welding,
which can impair welding ability.

Low temperature

If the temperature is too low, the viscosity of the welding paste may increase. This can cause
undesirable printing effects such as mold release, curling, and print gap problems, where the welding
paste is too solidified for accurate printing.

Acceptable ranges and conditions

Experts have different recommendations for relative humidity (Rh) and temperature ranges. Some experts
recommend wider relative humidity ranges, such as 35-65%, 40-70%, or 20-50%. However, some experts point
out that exceeding the upper or lower RH limits of 60% may cause certain defects and affect the
product's lifespan. In reality, choosing an RH range is more about experience and preference, that
is, which humidity conditions are most suitable for a particular product.

For temperature, although experts are relatively consistent, it is generally agreed that welding paste
performs best at 68 to 78 degrees Fahrenheit (equivalent to the temperature range where the human body
feels comfortable). It is worth noting that different welding paste products may perform differently in
not the same environmental conditions. Therefore, it is wise to consider some flexibility when designing
products.

Monitoring

Certain geographical locations, such as extremely humid or dry areas, may require more advanced
environmental control measures. However, no matter where the factory is located, some climate control
strategies are always maintained.

Humidity Sensors: Investing in high-quality relative humidity (Rh) sensors is
essential, and it is also necessary to install these sensors correctly to ensure measurement accuracy.
Otherwise, even small fluctuations in humidity and temperature can become major and costly problems. In
addition, regular inspection of sensors is also important, especially in environments with high
humidity, where Rh sensors are more prone to failure.

Air conditioning/heating equipment: Investing in a good air conditioning and heating
system is essential. It's a long-term battle. If you can effectively regulate the temperature in
your room, you should consider the problems that may arise from temperature fluctuations. In addition,
dehumidification equipment is particularly important in high-humidity environments.

Nitrogen in reflow: Excessive humidity often causes unwanted oxidation of welding
paste. The use of nitrogen can effectively inhibit this oxidation reaction.

Moisture-sensitive components

Shenzhen Highqualitypcb: Moisture-sensitive components are another key consideration. In high-humidity
environments, moisture-sensitive electronic components should be exposed to the outside of the package
for as short a time as possible based on their sensitivity level. However, if the appropriate humidity
level can be maintained, this issue should be properly handled.