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PCBA cleaning process and cleaner

PCBA cleaning process and cleaner

In the electronic assembly process, the bare board needs to go through many processes to finally become PCBA, and any step during the period may be contaminated, resulting in a short circuit, leakage and a series of problems. Therefore, for electronic products, a reasonable cleaning is beneficial to improve the operational reliability of the product and improve the service life of the product. This article we will go over the comprehensive issues related to PCBA cleaning, as well as the recommended PCB cleaner.

1. PCBA cleaning process

PCBA manufacturing used in the cleaning process, for different levels of product requirements, the use of flux and after the process of the difference, the need to use the cleaning process and equipment is also different.

At present, the water-based cleaning agent is applied in the PCBA cleaning process, the more common cleaning processes are as follows.PCBA cleaning process

PCBA in-line cleaning process

The cleaning method controlled by the conveyor belt speed of the components continuously on the conveyor belt and production cycle time without interruption. It is suitable for cleaning of high volume PCBA, and the whole process of water-based cleaning, water-based rinsing and drying is completed online through different cavities.

Batch PCBA cleaning process

Batch cleaning process

As defined in IPC-CH-65B-CN, the batch cleaning process is a grouping of multiple parts or different batches of a part by controlled production time cycle.

Advantages of batch cleaning systems

● Smaller size, high utilization of energy.
● Low cost, lower usage of cleaning agents and versatility of the procedure, low energy consumption.
● Provides a wide range of adjustable cleaning processes. The possibility of varying not only the number of wash and rinse cycles, but also the ratio of these cycles.
● Significantly reduce operating costs while having a strict process control system.

Ultrasonic cleaning

Ultrasonic cleaning principle: ultrasonic cleaning is the use of ultrasonic energy in the detergent cavitation, acceleration and direct flow into the role, and the detergent on the super solubility of the combination of dirt, so that the dirt layer is dissolved, dispersed, emulsified, or stripped and achieve the purpose of cleaning.

“Cavitation erosion effect”: when the cavitation phenomenon occurs, tiny bubbles from the generation, growth and rapid rupture of the instant formation of more than 1000 atmospheres of instantaneous high pressure, continuous instantaneous high pressure is like a series of small bombs constantly bombard the surface of the cleaning object, so that the object performance, crevices and blind holes in the attachment of dirt quickly peeled off.

Ultrasonic cleaning process

1. Loading
2. Cleaning tank. Cleaning agent cleaning (one or more times)
3. Rinsing tank. Deionized water rinsing (one or more times)
4. Drying tank. Wind cutting or hot air
5. Unload

Ultrasonic cleaning process features

1. One or more cavities to complete the water-based cleaning, water-based rinsing, drying all processes.
2. Can be used to clean the tray high height low, the bottom gap narrow assembly structure.
3. Cleaning in the ultrasonic effectiveness of the best temperature near the effect of optimizing.

Blister Cleaning

Blister cleaning systems usually use ultrasonic energy or immersion jets for agitation. Depending on the position of the sensor, ultrasonic agitation can be made very sensitive to the shape, so it is important that the sensor is assembled in the correct position.

Batch immersion cleaning equipment is a series of individual cleaning cylinders or a series of cleaning modules for integration. It is suitable for some small batch or no high cleanliness requirements of PCBA cleaning.

2. PCBA cleaning effect evaluation

PCBA cleaning effect evaluation

Pollution of PCBA

Contamination is defined as any surface deposits, impurities, slag and adsorbed materials that reduce the chemical, physical or electrical properties of PCBA to a substandard level. The main aspects are as follows.

(1) The components that make up the PCBA, the pollution or oxidation of the PCB itself will bring about the contamination of the PCBA board.
(2) Residues generated by fluxes during the manufacturing process, which are also major contaminants.
(3) Hand imprints, chain claws and jig imprints produced during the soldering process, and other types of contaminants such as hole plugging adhesive, high temperature tape, hand traces and flying dust.
(4) Dust, water and solvent vapors, fumes, tiny particles of organic matter in the workplace, and contamination from charged particles attached to PCBA caused by static electricity.

The harm of contamination

Contamination may directly or indirectly cause potential risks to PCBA, such as
(1) Organic acids in the residue may cause corrosion to PCBA.
(2) Electric ions in the residue in the process of energization, due to the potential difference between the solder joints caused by electromigration, so that the product short-circuit failure.
(3) Residues affect the coating effect.
(4) After time and environmental temperature changes, the coating cracks and warps, thus causing reliability problems.

Pollution caused by PCBA failure of typical problems

(1) Corrosion
PCBA assembly is the use of iron substrate bottom lead foot components, iron substrate due to the lack of solder bottom cover, in the halogen ions and moisture corrosion quickly generated Fe3 + , so that the board surface reddened.
In addition, in a humid environment, acidic ionic contaminants can also directly corrode copper leads, solder joints and components, resulting in circuit failure.

(2) Electromigration
If there is ionic contamination on the surface of the PCBA, it is easy to electromigration phenomenon, ionized metal to the opposite electrode between the movement, and in the reverse end of the return to the original metal and dendritic phenomenon called dendritic distribution, (dendrites, dendrites, tin whiskers), the growth of dendrites may cause a local short circuit.

(3) Poor electrical contact
In the PCBA assembly process, some resins such as rosin-type residues often contaminate the gold finger or other connectors, in the PCBA work heat or hot climate, the residue will produce sticky, easy to adsorb dust or impurities, causing increased contact resistance or even open-circuit failure. bga solder joints in the pads of the PCB surface corrosion of the nickel layer and the presence of nickel layer surface phosphorus-rich layer reduces the solder joints and pads Mechanical bonding strength, when subjected to normal stress cracking occurs, resulting in point contact failure.

3. Necessity of PCBA cleaning

(1) Appearance and electrical performance requirements
The most intuitive impact of PCBA contaminants is the appearance of PCBA, if placed or used in a high temperature and high humidity environment, there may be residues of moisture absorption whitening phenomenon. Due to the extensive use of leadless chips, micro BGA, chip-level package (CSP) and 01005 in the components, the distance between the components and the board is reduced, the size miniaturized, and the assembly density is increasing. If the halide is hidden under the component where cleaning is not possible, local cleaning may result in disastrous consequences due to the release of halide.

(2) The need for three-proof paint coating
Resin residues that are not cleaned off before surface coating can cause delamination or cracks in the protective layer; active agent residues may cause electrochemical migration beneath the coating, resulting in a ruptured protective coating failure. Studies have shown that the coating bonding rate can be increased by 50% by cleaning.

(3) No-clean also needs to be cleaned
According to current standards, the term no-clean means that the residue of the board is chemically safe and will not have any effect on the board production line and can be left on the board. Detection of corrosion, SIR, electromigration and other specialized tests are mainly used to determine the halogen / halide content, and thus determine the safety of the clean-free assembly after the completion of the assembly.

However, even if the use of low solid content of no-clean flux, there will still be more or less residue, for the high reliability requirements of the product in terms of the board is not allowed any residue or contaminants. For military applications, even no-clean electronic assemblies are required to be cleaned.

4. Cleanliness requirements

Electronics manufacturers are faced with a difficult choice about the level of cleanliness required to produce reliable hardware. The question of “how clean is clean enough” brings more challenges to the increasingly narrow wires and lines. What is an acceptable level of cleanliness in one area of industry (such as a toy after SMT wave soldering) may not be acceptable for another area (such as flip chip packaging).

Many process professionals may not know much about cleanliness, and the challenge remains to determine how much residue affects the functionality of the hardware, or some aspect of long-term reliability related to residue.
There are several factors to consider, such as.
(1) End-use environment (aerospace, medical, military, automotive, IT, etc.)
(2) The design/service life of the product (90 days, 3 years, 20 years, 50 years, shelf life + 1 day)
(3) Technology involved (high frequency, high impedance, power supply)
(4) Failure phenomena corresponding to the end product classes 1, 2, and 3 as defined by the standard (e.g., cell phones, heart rate regulators)

5. PCBA Cleaning Considerations

1.The detection and analysis of residues after welding/cleaning is an important part of the component cleaning process.
2、Component geometry
3、The height of the device tray height and the impact on cleaning
4、The entrapped liquid
5、Component problems and residues
6、Contaminants from the components
7、Component degradation
8、Other components cleaning consideration points
9、Wetting of the surface
10、Surface tension and capillary force
11、Filling gap compared to unfilled gap
12, flux residue variability
13、Cleaner effect

6. Water-based cleaning agent

Water-based cleaning agent: is deionized water as the main solvent, with surfactants, co-solvents, additives and other combinations, with the help of containing surfactants, emulsifiers, penetrating agents, such as wetting, emulsification, penetration, dispersion, solubilization and other effects to achieve the cleaning of pollutants of a cleaning medium, IPC definition of deionized water is not less than 50%.

Water-based cleaning: As defined in IPC-CH-65B-CN, water-based cleaning is a process in which the components are cleaned first with pure water or organic or inorganic saponifiers, and then the effluent is rinsed off the components with pure water.

7. Application of water-based cleaning agents

With the miniaturization of components, component placement and structure of high density, the introduction of lead-free technology, increasingly stringent environmental and material control, promote the rapid development of water-based cleaning agents, water-based cleaning agents used in the SMT cleaning process has been very mature, and reflects the considerable advantages.Application of water-based cleaning agents

Offline Cleaning Of Stencil

Applicable water-based cleaning agent products: neutral water-based cleaning agent
Cleaning objects : Solder paste printing stencil and red glue printing plastic mesh. Before reflow soldering solder paste residue cleaning, uncured residual red glue cleaning, misprinted board cleaning.
Cleaning equipment: Ultrasonic cleaning machine Ultrasonic stencil cleaning machine, spray type stencil cleaning machine

Online Cleaning Of Stencil

Applicable water-based cleaning agent products: Neutral water-based cleaning agent
Cleaning object : Mainly used for cleaning SMT printing machine stencil and misprinted board on the residue of solder paste cleaning

Reflow Chamber Cleaning

Applicable water-based cleaning agent products: alkaline water-based cleaning agent
Cleaning objects: reflow oven wave soldering chamber was baked in a variety of flux residue cleaning, rosin, oil and other relatively stubborn residual material cleaning.

Jig Carrier Cleaning

Applicable water-based cleaning agent products: Alkaline water-based cleaning agent
Cleaning object: Flux baked on cyclone, welding jig, fixture, condenser tube, and rosin, oil, etc.
Cleaning equipment: Fixture cleaning machine, spraying cleaning machine suitable for workpiece external surface cleaning.

PCBA Cleaning

Applicable water-based cleaning agent products: Alkaline water-based cleaning agent
Cleaning objects: cleaning of rosin flux residue, cleaning of water-soluble flux residue, cleaning of no-clean flux/solder paste residue, fingerprints, oil, dust and other pollutants on the surface of PCBA after SMT/THT soldering
Cleaning equipment: batch cleaning equipment (multi-slot ultrasonic spray cleaner,), continuous (online) cleaning equipment

Conclusion

The evolving electronics market can see that modern and future electronic products are more demanding than ever for miniaturization, high performance and high reliability. Thorough cleaning is a very important and technically very strong work, it directly affects the working life and reliability of electronic products, but also related to the protection of the environment and human health, so to re-understand and solve the problem of welding cleaning from the perspective of the entire production process system.

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