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Washable solder paste
Water-washed solder paste plays an increasingly critical role in the production of circuit board soldering. On the one hand, after the PCBA connection of the water-washed solder paste soldering is completed, it can be directly cleaned directly through the circuit board cleaning equipment, which is convenient and fast. On the other hand, water-washed tin The paste is a non-corrosive flux and paste. The solder residue does not affect the environmental protection and does not cause pollution to the environment. There are two types of washable solder pastes, lead and lead-free. Choose the appropriate type of solder paste according to different needs.
1. Ingredients of water-washed solder paste
The water-washed solder paste is made of the following raw materials in parts by weight: fatty alcohol polyoxyethylene ether 3-4, sodium cumene 3-4, coco diethanolamide 5-6, ethanol 40-50, Tween 803-5, lauryl alcohol 4-5, sodium malate 2-3, acetic acid 2-3, additives 4-5, deionized water 100-120. The cleaning agent of the present invention has strong compatibilization, anti-static, anti-corrosion, and slow pH value
1. Application of water-washable solder paste
Solder paste is a kind of solder material, mainly used in the PCBASMT industry. Its broad categories include water-washable solder paste and no-clean solder paste. Most of the solder pastes currently on the market are no-clean solder paste, which is washed by water. The surface understanding of solder paste is solder paste that can be washed with water, also called water-soluble solder paste.
2. How to use water-washed solder paste
First wipe the solder joints clean, apply a little solder paste, and then eat some solder with a soldering iron. Use a pinch to press the wires or pins on the solder joints. Use the tip of the soldering iron to gently press the solder joints to allow enough tin to flow. After soldering the joint, quickly remove the soldering iron. After the soldering iron is removed, wait for the tin to cool and settle before releasing the pin! When using, add proper amount of solder paste and scrape it on the stencil.
The amount of solder paste on the stencil is kept at about 1CM. And keep the spatula and the container clean at all times. The remaining solder paste in the container after opening must be sealed. If it is used continuously, it should be placed in the working room, and new solder paste can be obtained when it is used up. 5.3.4 If the reheating time exceeds 12 hours, it needs to be returned to the refrigerator and the bottling should not exceed 2/3 of the empty bottle. After placing it in the refrigerator for 4 hours, use it according to 5.4.6. If special reasons cause the production line to stop the solder paste, such as stop If it takes more than 1 hour, it must be returned to a clean tin paste bottle and sealed, and the sealing time must be stored in the designated location of the refrigerator. The printed solder paste substrate must be burned within 2H, if it exceeds 2H, it needs to be cleaned and restarted. Printing. When the unused solder paste is used again, try to mix it with the ratio of 1/4 of the old solder paste and 3/4 of the new solder paste, and try to use it on models with IC pitch greater than 0.5mm.
Fourth, the disadvantages of water-washed solder paste
There are currently two types of solder pastes on the market: water-washable solder paste and no-clean solder paste.
5.1. Does the water-washable solder paste only need to be cleaned with pure water? After cleaning, is there any follow-up treatment required? Is it suitable for circuit board welding with high frequency characteristics?
5.2. Is there no residue after reflow soldering of no-clean solder paste? Will there be burrs or electromigration in extreme environments (such as humidity)? Is it suitable for circuit board welding with high frequency characteristics? .
Five, the advantages of water-washed solder paste
5.1. The biggest feature of water-washable solder paste is that it can be washed. The washing is to soak the circuit board in water or alcohol for 5 minutes after soldering to clean the residue with a brush, and then rinse it again. After cleaning, Use 60-80 degrees hot air to dry the circuit board or dry it naturally. This is a washing method. In addition, general patch manufacturers have regulations on the cleaning time of this water-washed solder paste, which must be cleaned within four hours, otherwise there will be a danger of white powder (white residue); generally there is no problem within four hours. After cleaning it out The solder joints are very bright and the board surface is also very clean. It can be washed with a PCBA water washing machine. The general principle is to first rinse with tap water, then rinse with DI water, and finally blow it with an air knife.
5.22. The water-washed solder paste is non-corrosive flux and paste, and the solder residue does not affect the impedance value of the product, and there is no problem of corrosion of the solder joints after long-term use. The water-washed solder paste residue has the problem of corroding the solder joints and has a certain influence on the impedance value.
Sixth, the reason why the water-washed solder paste printing does not form
6.1 Solder paste collapse
The printed solder paste is not enough to maintain a stable shape, and the edges collapse and gradually spread to the outside of the pad, forming a connection between adjacent pads. If this phenomenon cannot be corrected in time, a solder short circuit will definitely occur after reflow.
6.2 Improper solder paste coverage area
The coverage area refers to the area on the pad surface that needs to be covered with solder paste. Theoretically, the area of this area is equivalent to the area of the stencil opening. But in fact, the solder paste coverage on the pad may be smaller or larger than the stencil opening. When the area covered by the solder paste is smaller than the pad, it may lead to a low tin condition; otherwise, it may cause a short circuit or an excessive tin problem.
6.3 Solder paste short circuit
The solder paste connection between adjacent pads on the PCBA board is called wet bridging. Due to the surface tension of the solder when it melts, sometimes the wet bridge will automatically separate during the reflow soldering process. If it cannot be separated, it will form a short circuit defect.
6.4 Solder paste offset
The printed solder paste is not completely aligned with the actual pad position, which may cause bridging, or may cause the solder to be printed on the solder mask, thereby forming a solder ball.
Seven, water-washed solder paste production and supplier
Eight, the difference between water-washed solder paste and no-wash
8.1 No-cleaning refers to the use of low solid content, non-corrosive flux in the production of electronic equipment, soldering in an inert gas environment, and the residue on the circuit board after soldering is minimal, non-corrosive, and has a very high surface insulation resistance, Under normal circumstances, it can reach the standard of ion cleanliness without cleaning, and can directly enter the process technology of the next process.
8.2 No-clean solder paste is made of special solder paste and spherical tin powder with very little oxide content. It has excellent continuous printing resolution; the flux paste contained in it uses a highly reliable low-ion activator system, so that it has very few residues after reflow and has a fairly high insulation resistance, even if it is free Washing can also have extremely high reliability.
8.3 After the no-clean solder paste is soldered, the PCB surface is relatively smooth and has less residue. It has passed various electrical performance technical tests and does not need to be cleaned again; the flux residue of this solder paste is not easy to combine with water, even if it is damp The insulation resistance is also very high, there will be no short-circuit phenomenon and the phenomenon of erosion of the substrate. So there is no need to clean.
Nine, why water-soluble solder paste can be washed with water
Water-soluble solder paste can be understood as a solder paste that does not need to be cleaned after soldering, but in fact, after soldering, the PCB surface is relatively smooth and has less residue. It can be tested by various electrical performance technologies and does not need to be cleaned again; this type of tin Because the flux residue of the paste is not easy to combine with water, its insulation resistance is very high even after being damp, and there will be no short-circuit phenomenon and the phenomenon of erosion of the substrate. So there is no need to clean it.
10. The price of washed solder paste
The selling price of water-washed solder paste is related to the customer demand. If the quantity is large, it is 10 yuan per kilogram, and the small quantity is 20 yuan per kilogram. The wholesale price is 15 yuan/kg.
