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The correct way to choose the humidifier in SMT workshop
PCBA Tech
The correct way to choose the humidifier in SMT workshop

The correct way to choose the humidifier in SMT workshop

2021-11-09
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Author:Downs

With the vigorous development of the electronic information industry and the corresponding fierce competition and challenges, more and more companies have begun to discover and pay attention to the importance of the "workshop environment" to the optimization of production processes. Taking the SMT workshop as an example, in order to ensure the normal operation and assembly quality of the equipment, certain standards are generally required for the cleanliness, temperature and humidity of the environment; however, compared with the mature workshop cleaning and temperature control technology, the existing domestic The humidifier technology often makes many companies feel a little unsatisfactory. So, today let us discuss from three aspects, how to choose the right humidifier for the electronics factory and SMT workshop.

Hidden costs of electronics factories and SMT workshops

——The invisible cost is also amazing

Many domestic electronics factories and SMT workshops, which are not mature enough, understand the "workshop environmental standards" as follows: 1-SMT process equipment requirements, 2-national standard "hard" regulations; therefore, some companies "visible" in order to save The cost of the workshop environment is not strict or even disregarded; afterwards, many welding quality, production technology, product safety and other issues have been created invisibly, resulting in a high rate of defective products, and it is difficult for practitioners to detect them. The real reason.

Taking humidity as an example, the requirement for humidity setting in SMT workshop is 50%±10%RH, which is mainly based on:

pcb board

1. If the humidity is too high, the components are easy to absorb moisture, which is not good for moisture-sensitive components. At the same time, the solder paste is also easy to absorb moisture when exposed to moist air, causing soldering defects;

2. The humidity is too low, the air is dry, it is easy to generate static electricity, which is not good for electrostatic sensitive (ESD) components; the existence of this kind of static electricity (charged) phenomenon, on the one hand, may cause the surface charge of the object to attract the particles of the opposite sex in the air. , Causing degradation of the insulation performance of electronic sensitive components, structural corrosion or destruction; on the other hand, when the external conditions are suitable, this accumulated charge will also generate electrostatic discharge, causing partial damage or breakdown of the components, and in severe cases, it will also cause Fire, explosion, etc.

Humidity and humidity

——A little difference, a thousand miles away

When electronics factories and SMT workshops began to gradually show the need for environmental humidity control, humidifier suppliers in SMT workshops have sprung up, and many companies do not know how to choose; but from a process point of view, domestic SMT workshop humidifiers are the most common It is spray humidification, which is divided into ultrasonic spray and electric spray.

The feature of the spray humidifier is that the water is atomized by ultrasonic vibration or heating, and the scene of equipment swallowing and spitting fog can be clearly seen during use; from the perspective of industrial application, the advantages of this type of humidifier are: the initial investment cost is relatively The lower, short-term "humidification" effect is obvious (that is, you can see the change in the value of the humidity meter soon). However, many companies that have installed spray humidifiers have responded. The disadvantages of this type of humidifier are: on the one hand, it is impossible to control the equilibrium value of humidity. On the other hand, after long-term use, electronic components will still be found to have structural corrosion or corrosion. Destruction phenomenon.

This phenomenon is mainly due to the humidification performed by spraying. The particle diameter of liquid water entering the air is thousands of times larger than that of normal water molecules in the air. Therefore, although the humidity meter can be changed more quickly, It is also easier to condense into liquid water droplets; when the liquid water droplets adhere to the equipment or product components, it will take longer to overmoist or corrode. Regarding spray humidification, Hunan Satellite TV’s “News for the Truth” section did an experiment earlier. The spray humidifier was turned on next to the TV. After a certain period of time, the TV exploded for the same reason.

Therefore, for some electronic or damp-prone product production workshops, this type of spray humidifier should be used with caution.

Due to the fatal flaws in the application of spray humidification in the electronics industry, in recent years, more and more SMT workshops have begun to pay attention to the wet film humidification process. The principle is to increase the water surface by increasing the air flow rate on the water surface and increasing the water-air contact surface area The evaporation rate.

In terms of process principle, the advantages of this type of wet film humidifier are: the humidification effect is closer to the natural vapor form of the air, and the intelligent humidity control makes it easier to keep the indoor humidity at a relatively balanced value; for example, the Vatican Museum in Rome uses the German BRUNE Wet film humidifier.

But the shortcomings are also very embarrassing: because the core of this type of humidifier is the wet film. In addition to the function of absorbing water and adsorbing large particles in the air, the most important thing is its water-locking function; when the surface of the water is air When the flow rate reaches a certain value, ensure that the water enters the air in the form of water vapor; however, the practical application effect of the common metal wet film in China is difficult to achieve. We compare the parameters of the German BRUNE humidifier with a domestic wet film humidifier:

Since there is no national standard for humidification process in China, the above data like "humidification rate: 12 L/h" will appear. It seems that in a limited space (the target is applicable max: 180m2), 12L of water vapor enters the air every hour What is the concept? Matching with this type of "humidification rate" is the data "air volume: 6000m3/h". Therefore, some companies that use domestic wet film humidification equipment often feel that although compared with spray humidification, the equipment is no longer visible, but the phenomenon of humidity, influence on welding, corrosion of components, and equipment is still unavoidable. In fact, this phenomenon is not difficult to understand. Judging from the parameters provided by domestic wet film humidifiers, such high air volume and water consumption can only show that a large amount of water is still blown into the air in liquid form.

Relatively speaking, the BRUNE humidifier, a veteran industry in Germany, is at least much more reasonable in terms of parameters, and when the air outlet is tested for humidity, on the one hand, the value of the humidity meter can be seen to increase rapidly, on the other hand, there is no sign of humidity at all.

Therefore, for the selection of humidifiers in SMT workshops, it is recommended to learn to judge the "reasonability" of the realization of equipment parameters.

List your requirements

-To choose the right humidifier

After having a basic understanding of domestic humidification equipment, we returned to the original question, "How do electronics factories and SMT workshops choose humidifiers correctly?". The following suggestions:

1. Understand the characteristics of workshop equipment and products, and make a preliminary judgment on which type of equipment is more suitable for spray humidification and wet film humidification;

2. Judgment parameters, generally recommended key reference: applicable area, humidification rate, water storage, power; especially "humidification rate", normal humidification requires a relatively "reasonable value", not the larger the better; "power" is the process of use For the judgment of medium energy consumption, take the German BRUNE humidifier as an example. Under the same applicable area humidification condition, the power of domestic humidification equipment is generally 4-14 times that of the BRUNE humidifier.

3. Refer to the equipment material, some SMT workshop humidifiers will use stainless steel as the equipment shell. Although the initial investment cost is slightly lower, in actual use, water and impurities filtered into the water will corrode the stainless steel material, which will directly affect the humidifier. In the normal service life of the battery, the cost invisibly will be greater.