Among the 6 process input identified in manufacturing
process, environment is the most powerful and the most difficult to
control. It is nearly impossible to
fully control the force of nature. The
elements of environment which have major impacts to process output are temperature,
humidity, air particle and electro static discharge (ESD). Sometimes all these
elements could have relationship with each other.
Environment control is apply to 2 areas,
- Ambient condition in production floor
- Localized environment control confine to only one process in specialize manufacturing equipment. Confine environmental control to one unit operation is more stringent than ambient condition.
Temperature
According to Wikipedia definition temperature it is a
measurement of how hot or cold the object is and can be measured using
thermometer. In manufacturing, control
of temperature is important due to
- Use of heat sensitive material such electrical component, chemical will experience accelerated deterioration under high temperature
- Impact on worker productivity - temperature must in comfortable zone for worker
- Temperature affect relative humidity and relative humidity affect ESD. Refer to below for more detail explanation.
Temperature can be controlled to certain extend by using
air conditioning or heater depending on the requirement of the process.
Humidity
Humidity is the amount moisture in the air. One of the universal methods to measure humidity
is using relative humidity. Relative
humidity (RH) compare the actual amount of water in the air to the maximum
amount of water the air can hold and it is express in percentage (%). RH give an indication of water saturation in
the air, 100% means that water vapor in
the air had reach its maximum capacity.
RH is inversely related to air temperature, the same amount of water vapor
in the air will have different RH reading at different temperature. The lower the temperature, the higher the RH
and vice versa.
 |
| Different amount of water vapor in same amount of space, the higher the amount of water vapor the higher the RH |
Presence of water vapor in the air has an influence on
manufacturing process and product quality.
Below are some common examples of the humidity impact which I have
personally experience in different manufacturing process and product. I would welcome addition from my
readers.
- Soldering process in PCBA assembly.
- PCBA moisture sensitive device (MSD) component.
- Photolithography process in wafer and LCD fabrication due to some photo resists used is very sensitive to moisture and cause high variation in critical dimension on the output.
- Battery cell making process such as electrode coating and jelly roll forming, electrolyte filling. Moisture could cause failure and in worst case it could cause safety hazard.
- Plastic molding process.
- Paint curing process as moisture would prolong paint curing time in turn if paint is not properly, the surface will become more scratch.
- Low RH will generate greater electric static discharge (ESD) which would injure ESD sensitive components.
- Humidity will accelerate the oxidation of metal parts such as component leads thru water vapor condensation.
Humidity is control thru adjustment of temperature and
ventilation.
In the next article we will study about another 2 environmental impact, electric static discharge and air
particles.
