The solder slag anti-oxidation reduction additive is gradually becoming one of the indispensable auxiliary materials in the electronic assembly wave soldering technology process. It is placed on the surface of the liquid solder to reduce the oxygen exposed to the air on the surface of the liquid solder. The protective effect prevents the liquid soldering tin from oxidizing and reducing the tin slag to remove surface impurities and reduce the amount of tin slag, thereby achieving the purpose of reducing the production cost of the liquid soldering tin. This article introduces the causes, hazards, and role, classification, performance requirements, and evaluation methods of anti-oxidation reduction additives for solder slag, which helps to choose anti-oxidation reduction additives for solder slag in actual production.

1. Introduction:In the electronics manufacturing process, the wave soldering process is indispensable and plays a critical role in the welding quality of electronic products. The characteristics of the wave soldering process determine that a large amount of tin slag will be continuously produced during the soldering process. Not only directly affect product quality, but also cause a huge waste of soldering production costs. After a long period of continuous research, it was found that the use of solder slag antioxidants is the most effective measure to solve the problem of tin slag.As people pay more and more attention to the anti-oxidation reduction additive of solder slag in recent years, according to statistics, about 35% of electronics companies are currently evaluating or using such products. It has become one of the indispensable auxiliary materials in the electronic assembly wave soldering technology process. Because solder slag antioxidants are new products, many people know very little about them (including companies that are already in use), which makes them very passive in the evaluation or use process. Unnecessary losses, so it is important to fully understand the solder slag antioxidant products and choose the right supplier.

2. Background of production of antioxidation reduction additive for solder slag:

2.1.) Source of tin slag:The characteristics of the wave soldering process determine that during the soldering process, new liquid solder surfaces are constantly exposed to the air, and the molten solder is in contact with oxygen in the air in a flowing state and continuously oxidizes to form tin oxide slag; solder tin oxide slag It is mainly a mixture of alloy solder oxide and a large amount of alloy solder, which is continuously generated and accumulated on the surface of molten alloy solder.

2.1.1.) Flux residue;

2.1.2.) Other solder compounds.

2.2.) Hazard of tin slag:

2.2.1.) Affects the fluidity of the tin and the height of the tin surface, and affects the welding quality;

2.2.2.) Adhering to the surface of the board, causing quality problems such as solder balls, directly affecting the electrical reliability of electronic products;

2.3 2.2.3) The handling and transportation of tin slag causes additional management problems and causes harm to the environment and human body;

2.2.4.) Loose oxide slag makes it easier for air to stay in the molten solder, thereby intensifying the oxidation of the solder;

2.2.5.) Useful metals are wrapped by tin slag and cannot be used, causing great waste.

3.The role and classification of anti-oxidation reduction additive products for solder slag:

3.1.) The role of solder slag anti-oxidation reduction additive products:

3.1.1.) Combining the tin oxide slag (tin) produced in the soldering furnace with the solid-liquid suspension gravity sedimentation system is based on natural forces, so as to maximize the dissolution and reduction and reduce the amount of solder;

3.1.2.) Reduce the exposure of the surface of the liquid solder to oxygen in the air to protect it, enhance the fluidity of the solder, and improve the quality of the solder. (No need to change, it is better to use the original)

3.2.) Classification of Antioxidation Reduction Auxiliary Products for Solder Slag:Solder slag anti-oxidation reduction additive products are currently on the market in a variety of styles, but these products have different performance. According to the composition, it can be divided into: inorganic non-ionic minerals and organic anionic polyethers. In terms of function and morphology, it can be mainly divided into two types: crystalline powder and liquid oil (ie, crystal and liquid). And the name is divided into: reducing agent, antioxidant, soldering surfactant and reducing oil.

3.2.1.) Inorganic non-ionic minerals (ie crystals):

Minerals are generally crystalline products. In the process of use, the element N has a greater affinity for oxygen, and the replacement reaction is used to achieve deoxidation, which further improves the oxidation resistance of the solder. The second is through the F in the material. Both element and element B achieve reduction through high-temperature displacement reactions. Their polar solubility can dissolve ionic compounds and dissociated covalent compounds. In combination with solid-liquid suspension gravity sedimentation system, natural forces are used to maximize dissolution and reduction. Due to the large amount of tin slag accumulation in the furnace, the dual action of N element has greatly enhanced the fluidity and wettability of liquid tin, thereby improving the welding quality process. The cleaning cycle is generally 10 hours over time until the active agent is consumed and removed. The soldering surfactant does not react with the metal, but only with the oxide slag, which is less odorless. When the metal oxide in the tin oxide slag is dissolved, the interconnected metal oxide arrangement is open, and any useful metal trapped in the slag can be dispersed and flowed back into the liquid solder without being affected by the solder surface. Effects of active agents. 10 hours can control the amount of tin slag less than 0.6kg per unit, the tin content of tin slag is less than 0.3%. Of course, it is not all good. The disadvantage is that the product’s professional counseling, on-site operator mentality, and operating tools will directly affect the use of the product.

3.2.2.) Organic anionic polyethers (ie liquids):

Polyethers are generally liquid oily products. During use, they undergo a reduction reaction with SnO2 and SnO in tin oxide slag. The disadvantages are: first, the single reduction function cannot prevent antioxidants in advance; second, the liquid products are in During use and the final tin slag is in the form of mud, and it feels dirty, which is not conducive to recycling; again, it will produce a large irritating odor and smoke during use, which is harmful to the human body and the environment; The volatilized gas may be left on the PCB, which will adversely affect the product quality. Finally, an auxiliary stirring device needs to be added during use, which is not convenient in operation. In particular, polyethers are subject to the REACH regulations.

4. General requirements and evaluation of anti-oxidation reduction additive products for solder slag:

4.1.) Requirements of anti-oxidation reduction additive products for solder slag:It can be seen from the above that no matter which type of solder slag oxidation-reduction additive product has some disadvantages during use, a good solder slag oxidation-reduction additive product must meet the following requirements:

4.1.1.) Non-toxic and harmless, comply with relevant environmental protection laws and regulations (RoHS, REACH, ISO14001, OHSMS18001, etc.);

4.1.2.) Easy to store and comply with sea, road and air transportation regulations;

4.1.3.) Convenient and tidy to use without causing second pollution;

4.1.4.) It is harmless to the equipment and will not affect the wave soldering machine during processing;

4.1.5.) Guarantee product quality without affecting PCB solder joints and board surface;

4.1.6.) Safe to use, not flammable and explosive.

4.2.) Evaluation of solder slag antioxidation reduction additive products:

4.2.1.) Material composition: must meet ROHS (Cd 100ppm, Pb 1000ppm, Hg 1000ppm, Cr 1000ppm, PBB 1000ppm, PBDE 1000ppm), halogen (GI≤900ppm, Br≤900ppm and GI + Br≤1500ppm), REACH and other Legal and regulatory requirements. Because different companies have different standard limit requirements, the specific judgment standard depends on the actual situation of the company.

4.2.2.) Physicochemical properties: The density, viscosity, specific gravity, humidity, flash point, odor and color of the material are stable at a temperature of 5–45 ° C, meanwhile, they are lighter than tin, and their limit values ​​(temperature resistance) Coefficient) to at least 280 ° C and above.

4.2.3.) Solder and tin slag composition content: Take the previous tin nuggets and tin slag for component inspection and comparison to evaluate whether the solder slag anti-oxidation reduction additive product will change its original composition (including addition or reduction) and whether The presence of some of this harmful (or restricted) substance.

4.2.4.) Solderability: It is expressed in terms of expansion rate. According to the standards of the flux industry, it is generally controlled at 80%-92%. Therefore, the solderability of the solder after the use of solder slag oxidation reduction additive products The test value of the solderability of liquid tin must also be achieved before use. If the anti-oxidation reduction additive of the solder slag indicates that it has enhanced solderability of liquid tin, the actual detected value should be greater than the original (before use) test value.

4.2.4.) Corrosiveness:

4.2.4.1.) For PCB: In order to ensure product quality, the anti-oxidation reduction additive of solder slag cannot cause any corrosion to the PCB or the solder joint. The copper corrosion test reflects the corrosiveness of the residue during the soldering process. The test refers to the GB / T9491-2001 standard. The test conditions are: temperature 22 ℃, humidity 70% RH, air pressure 101KPa, time 2 days (48 hours); the corrosion test of the copper plate reflects the corrosiveness of the residue after welding. The test reference JISZ3197-99 standard, test conditions: temperature 22–25 ° C, humidity 58–60% RH, air pressure 101KPa, time 10 days (generally 7-10 days).

4.2.4.2.) For equipment: The corrosion problem of wave soldering equipment has always existed and had a headache. Since the corrosion problem involves many aspects, and there is no specific standard in this regard, it is difficult when corrosion occurs. Accountability. In order not to break the existing balance and ensure the integrity of the equipment, it is necessary to ensure that the solder slag oxidation-reduction additive and wave soldering equipment are not corrosive. At present, wave soldering equipment on the market is mainly made of stainless steel and titanium alloy materials, so it is necessary to confirm the corrosion rate of the anti-oxidation reduction additive of the solder slag to the stainless steel and titanium alloy materials, and detect pure titanium or other specified in GB / T 3621 Grade titanium alloy; 304, 316 stainless steel specified in JIS G4304; gray cast iron standard inspection and evaluation specified in GB / T 9493.

4.2.4.3.) Test standard: Take an appropriate amount of tin slag anti-oxidation reducing agent in a test container that has been thoroughly cleaned, and immerse all the treated test pieces in the solder slag anti-oxidation reduction additive. Alternatively, the test piece can also be tested first. Put it in a container and pour the solder slag anti-oxidation reduction additive. Take at least three parallel samples for each group of tests. The test piece should be placed in the middle of the anti-oxidation additive of the solder slag as much as possible, and it is not allowed to contact the container wall. In general, only one test piece can be placed in each container. If more than two test pieces are required, the test piece spacing It should be above 1cm. Put the container with the test piece in a high temperature box at 270 ° C for testing. During the test, the changes of the test piece and the anti-oxidation reduction aid of the solder slag should be frequently observed and recorded. If the anti-oxidation reduction aid of the solder slag is reduced, When the test piece is about to be exposed, it should be added in time. After the test time is reached, remove the test piece, rinse it with water / acetone (wash with water or acetone depending on the polarity of the anti-oxidation additive of the solder slag), and then wipe away the corrosion products with a brush, rubber utensil, etc., or use ultrasonic waves. Method for cleaning. If the corrosion products are not easy to remove, refer to the chemical or electrolytic method of GB / T 10124 Appendix B for removal. After the corrosion products are removed, the test piece is rinsed with deionized water, washed with acetone, dried quickly, stored in a desiccator, weighed and visually inspected after being placed at room temperature.

4.2.4.4.) Inspection and evaluation: Use a 20 × microscope to check the test piece for discoloration and signs of corrosion, such as corrosion pinholes, surface looseness, etc., and calculate according to the following formula.a. Corrosion rate:8.76 × 107 × (M-M1);

R = STD × 100% (7).

In the formula:

R——corrosion rate, mm / a;

M——the mass of the sample before the test, g;

M1——mass of the sample after the test, g;

S——total area of ​​test piece, cm2;

T——test time, h;

D——Density of test material, kg / m3.

4.2.5.) Insulation resistance: According to GB or JIS, the minimum SIR value must not be less than 1010, and J-STD-004 requires the minimum SIR value not to be less than 108. (Test conditions: temperature 85 ℃, humidity 85% RH, Direct test under 168H under DC50V). Due to different test methods, the two required test values ​​are not comparable.

4.2.6.) Electromigration: In order to ensure the insulation performance of the products produced by the solder slag oxidation-reduction additive after a long period of time and whether there are residual solder slag oxidation-reduction additive ions migrated for a long time, resulting in PCB or soldering. Pitting corrosion, discoloration and tin whisker generation. This project is based on IPC J-SID-004B technical requirements and IPC-TM-650 2.6.14.1 testing standard requirements (temperature 20–25 ° C, humidity 50–60% RH, air pressure 101KPa , Time 596H), check to confirm that the minimum SIR value must not be lower than 108 and whether there is electromigration (filament growth) and corrosion and discoloration between the electrodes.

4.2.7.) Metallographic section: Through this test, fully check whether the quality of the solder joint is abnormal after using the solder slag antioxidant.

2.8 4.2.8.) Tensile test of solder joints: Through this test, the welding strength of solder joints can be fully checked after the use of solder slag antioxidants.

2.9 4.2.9.) High temperature and high humidity: To ensure that the products produced by the anti-oxidation reduction additive of solder slag are used in some harsh environments, and there will be no quality problems due to the anti-oxidation reduction additive products of solder slag. Can be tested according to standard IPC-TM-650

2.1.1 (test conditions are generally: temperature 20–22 ° C, humidity 55-65% RH, air pressure 101KPa), and specific experimental conditions (temperature, humidity, time, power on or not) Etc.) need to be determined according to the company’s products and regulations.

4.2.10.) Residual ions on the surface: Residual elemental substances on the surface of the PCB, some substances may be affected by the environment or in the course of use, some reactions may occur, affecting the quality of the product, in addition, if the solder slag anti-oxidation reduction additive is harmful Or restricted substances remain on the surface of the product and affect the quality of the product. In order to avoid such problems, testing and confirmation are required. Specific ion detection items (26 items) can be selected by yourself.

4.2.11.) Smoke and odor detection at the use site: The product will cause product smoke and irritating odor during use, causing serious harm to people and the environment. Therefore, the use site environment must meet the control requirements of ISO14001 and OHSMS18001. The test items can be based on solder The composition and actual situation of the slag anti-oxidation reduction auxiliary will be confirmed on its own.

4.2.12.) Benefit evaluation: The main purpose of using the solder slag anti-oxidation reduction additive is to reduce the amount of tin slag generated and control the welding cost. Therefore, the benefit evaluation is an inevitable part. To evaluate the benefit value generated, the simplest The method is to use the amount of tin slag generated before and after use to calculate (calculation formula: (amount of tin slag before use-amount of tin slag after use) × tin price-amount of tin slag before use × 50% off the tin price (slag Recovery price)-Antioxidant reduction additive amount of solder slag × Unit price of antioxidation reduction additive for solder slag = cost savings).

25) Summary:

The solder slag anti-oxidation reduction additive will soon be the same as the flux, an essential material in the electronic wave soldering technology process, but because the product and industry are in the initiation stage, they are emerging industries and products, and there is no corresponding industry and international Standards, resulting in a wide variety of products, mixed fish and dragons, and different performances. In order to choose a good tin slag antioxidation reduction additive product in the actual production process, it is necessary to understand more about the functional characteristics, functions and composition of the tin slag antioxidation reduction additive product, and to fully evaluate the solder slag according to the existing conditions The comprehensive situation of various aspects of anti-oxidation and reduction additives, only in this way can we really choose good quality anti-oxidation and reduction additives for solder slag, which guarantees the company’s interests to the greatest extent, and also guarantees human and environmental health.