The temperature and humidity balance effect on solder paste printing in SMT workshop

Do you know why dust free workshop in SMT factory needs to control temperature and humidity? And what will be the consequency if we failed to keep the balance?

Why we need to keep balance of temperature and humidity?

In the production flow, different procedure require specific conditions of enviorment, thus we need to control temperature and humidity. Manufacturers can reduce the dust, germ and virus in the air to provide a good production enviorment of constant temperature, pressure and noise.

A clean room means to eliminate the corpuscules, harmful air, germ and other contaminants in the air and keep the temperature, cleanliness, pressure, air flow, noise, viberation and light, static control in a specific range. It is a workshop designed in requirement. The internal enviorment will keep stable no matter what the external environment changes.

The temperature and humidity standard in specific industries

SMT work shop: temperature: 23+/- celsius degree, humidity 30%~70%

This is mainly for the performance of solder paste. The temperature will have an effect on solder paste activity, it also have an impact on the activity of some of the solvent in the scaling powder. Higher temperature will increase its activity, then it will have a bad influence on surface mount and reflow. Cold solder joint and rugged solder point happens. The humidity will cause the absorb rate of water from air for solder paste, if aborb more than need water, then in reflow oven there will be joint soldering, air bubble problems. So to ensure smooth surface mount it will require a balance of temperature and humidity.

Electronics manufacturing work shop: termperature 22 celsius degree, reletive humidity 50%~60%

The workshop of chip manufacturing, Integrated circuit manufacturing and disk manufacturing is a key part in electronics manufacturing industry. The requirement of copuscules and dust is quite rigid in their manufacturing process.

For packing industry

There are two types: Food packaging and medicine packaging. For medicine production and packaging, the dust free level is 100/10K/100K/300K. And its relevant air circyling frequency is: 300~400times/h, 25~35times/h, 15~20times/h.


  • 20~23 celsius degree at summer for 100/10K PPM dust free level

  • 24~26 celsius degree at summer for 100K/300K PPM dust free level

If the temperature is below, there will be statics which will made IC short circuit, increase the defects rate.

According to industry data, more than 60% defects of SMT is caused by solder paste printing problem, so it is quite important for SMT work shop to control relevant process.