The new wave of green electronics - halogen-free

After the implementation of EU RoHS and China RoHS and lead-free process conversion, the new green electronic wave -- Halogen-free (free) sweeps the electronic and electrical industry again. In addition, Norway also issued a new directive on the Control of Hazardous Substances (PoHS), in the PoHS directive, has clearly restricted the use of 18 hazardous substances that must be excluded in related products. Among them, the first group is bromo-series noncombustible agents, including hexacyclobromododecane (HBCDD) and tetrabromopropanediol (TBBPA), which is most commonly used in printed circuit boards. In addition to international laws, ASUS, Dell, HP, Apple, Intel, AMD and other international manufacturers have also announced that they will introduce halogen-free materials from 2008. Halides are widely found in printed circuit boards, welding masks, molding compounds, connectors, and other common electronic products. Nowadays, people pay increasing attention to the problem of halogens and actively restrict the use of halogens in electronic products. For halogens from many different sources, and for the minimal environmental impact of low levels of halogens, most establishments use the content levels specified by the International Electrochemical Commission (IEC) as requirements for their final assembly products. Specific requirements are: chlorine compounds < 900 PPM. Bromine compounds < 900 PPM. Total halogen 1500ppm halogen free could be another green revolution in the electronics industry following the implementation of the RoHS (Hazardous Substance Restriction) Directive on 1 July 2006.

Halogen-free and clean - free flux series

With the rapid development of electronic industry and the increasingly fierce market, each enterprise pays more and more attention to the quality of products, and the weldability and cleaning problems caused by various metal materials and electronic components are common technical and quality problems of relevant enterprises. Flux is the key material to ensure the welding quality in the process of micro-electronic welding. It should not only have high welding aid, but also can not corrode the welding material, but also meet a series of mechanical and electrical properties requirements. Therefore, the quality of flux directly affects the quality of welding products.

Different types of flux, the welding effect, environmental pollution, the production cost and has a big difference in the final quality of the electrical appliances, and electronics industry to use more than the flux for rosin flux and water-soluble flux, rosin flux, in particular, its main composition is rosin, halogen and solvent, the flux residues after welding, corrosive, need to use freon, Chlorine hydrocarbon and other ODS material cleaning agent for cleaning, and a large number of such cleaning agent emissions will lead to the destruction of the ozone layer, direct harm to the human living environment. To protect the ozone layer and meet the requirements of SMT high density assembly, the use of no-cleaning welding technology is an effective way to save cleaning equipment, reduce manufacturing costs, simplify the process, and avoid the damage of cleaning agents to the environment. However, the effective way to realize the no-cleaning process is to use halogen free and low solid content no-cleaning flux.

First of all, halogen-free no-cleaning flux should meet the following requirements:

1, does not contain halogen and other harmful substances;

2, welding surface less residue, no viscosity, dry surface after welding;

3, with excellent solder, connectivity and moisture, solder joints full bright, good tin penetration, effectively prevent the occurrence of tin deficiency and short circuit (tin bridge);

4, contains a variety of additives, greatly reduce the probability of tin ball tin bead generation;

5, flux residue is low, no corrosive residues, no lead, no halogen, completely free from cleaning;

6, the surface insulation impedance is very high, in the case of no cleaning board insulation impedance is still in line with IPC test specifications, high electrical reliability;

7, the product is low smoke, does not pollute the working environment, does not affect the health;

8, the price is moderate, no need to change the process, replace the equipment, excellent versatility.

Scope of application

Suitable for SMD components, red adhesive chip mixed substrate and high-density DIP components installed substrate, low residue, halogen free.

Such as: power supply products, computer motherboard, computer peripheral products, communication products, household appliances, LCD TV, automotive electronics, instrumentation and other processes suitable for: spray, foam, sticky dip coating, suitable for automatic welding operations.

1.1 Selection of activator

To develop a flux with excellent performance, the activator with good performance and high efficiency should be selected first. Therefore, in the welding process activator immediately oxidation with the metal surface, so as to remove it, purify the metal surface so that the solder and welding between the solder joint firm and reliable, remove fake welding, virtual welding phenomenon, therefore, the activation is an important component of flux, but the activation rate of general activation is proportional to the corrosion, This gives no clean type of halogen-free flux activator of difficult choice, this kind of no clean flux activator must have used in the welding temperature can be volatile or decomposed into corrosive materials, make the wettability of lead-free solder ability strong, can enhance the weldability of the lead-free solder, can adapt to all kinds of lead-free solder welding temperature, the lead-free solder alloy non-corrosive effect, therefore, Traditional acid salts and inorganic salts as activator can't use, after repeated experiment and test, found the C2 - organic acid has a good activation performance of C10, especially through theoretical analysis, choose mixed acid, so that it can reduce the cost of activator, can according to need, again by adjusting the proportion of various components to control its boiling point, make its can volatilize completely after welding. Tongfang company has made many tests on the selection of varieties and dosage and achieved success. The volatilization temperature of activator can be controlled at 150℃-265℃, and the dosage at 0.7%-1.5% can achieve good results.

1.2 Solvent selection

The solvent used in traditional flux is too much water-soluble fatty alcohol, generally ethanol or isopropyl alcohol. But if a single isopropyl alcohol or hexyl alcohol as solvent, to obtain a good welding effect, in addition to the activator, must also be adding surface active agent, wetting agent, foaming agent and so on, these additives commonly high boiling point, it is difficult to completely evaporate after welding, it is inconsistent with the purpose of cleaning free, through trial production and performance test for many times, The above problems can be solved by using a composite solvent, i.e. water-soluble alcohols and insoluble ethers, because the ethers used have the following characteristics:

1) The surface insulation resistance can be increased.

2) Can play the role of surfactant and wetting agent.

3) It can resist higher temperature before welding in the preheating zone, and will not make the active substance volatilize before welding.

4) In the welding process can be completely volatile, which not only improves the performance of the flux and greatly simplifies the composition of the flux.

1.3 Technical specifications and physical properties of solvent-free halogen-free cleaning flux.

(1) Colorless transparent liquid or light yellow transparent liquid with low viscosity

(2) Relative density 0.795-0.820

(3) Acid value 16-25MgKOH /g

(4) No halogen content

(5) Solid content 1.5-8%

(6) Expansion rate > 80%

(7) Resistivity of water tap liquid > 1×10⁵ (ω.cm)

(8) Surface insulation resistance >1 ×10¹⁰ ω (according to JIS3283 standard)

(9) There is no corrosion in copper corrosion test.

1.4 Application Scope

Suitable for SMD components, red adhesive chip mixed substrate and high-density DIP components installed substrate, low residue, halogen free.

Such as: power products, communication products, household appliances, LCD TV, instruments and meters

Suitable for: spray, foam, adhesive coating, suitable for full automatic welding.

2, halogen free washing film forming water-based flux (TF SJ-5505 series)

At present, another major type used in microelectronics welding in the electronic industry is water-based flux. The disadvantage of this type of flux is that after the use of this kind of flux, the residue left on the panel is easily dissolved by moisture, resulting in the decline of insulation resistance performance, and the PCB surface becomes damp and white. This is one of the reasons that water-based flux is not as widely used as organic solvent-based flux so far.

This series of fluxes are water-based fluxes with halogen free, low solid, free washing and film forming, aiming at the shortcomings of VOC as solvent. It not only eliminates the safety and pollution problems of organic solvents, but also avoids the problem of water-based flux residues being susceptible to moisture dissolution and whitening, resulting in the decline of insulation impedance. After use, the flux can form a protective film on the PCB welding surface. The film is not water-soluble, which can prevent dampness and moistureproof, improve the insulation and extend the service life of the product. This series of water-based flux with high purity water as the main solvent, carefully and scientifically prepared, no VOC, to overcome the shortcomings of VOC as a solvent, non-toxic to the human body, no pollution to the environment, non-flammable, safer to use, to meet the requirements of environmental protection. And has excellent welding performance, after welding full solder spot, no connection, and PCB board surface clean, high impedance.

Lead-free solder paste series

With the development of electronic products to large-scale integration, digitalization and miniaturization, surface mounting technology (SMT) has become the mainstream technology of electronic assembly, and solder paste printing is SMT is the first process, which directly determines the quality of electronic products. Solder paste consists of superfine (20-75um) spherical alloy tin powder and flux system. Flux system as the suspension carrier of tin powder, so that the solder paste has a certain activity, viscoelasticity, thixotropy and other properties, flux system contains solvent, catalyst, surfactant, rheological regulator, heat stabilizer and so on. Sn-pb solder paste has excellent performance and low cost, so it has become the main welding material in electronic assembly welding. However, due to the large amount of lead, long-term use will bring great harm to human living environment and safety. Therefore, it has become a top priority to develop green solder paste without lead.

Lead-free solders shall meet the following conditions: Low melting point, alloy eutectic temperature is similar to the eutectic temperature of Sn63/Pb37 183℃, roughly between 180℃ and 220℃, non-toxic and environmental pollution, thermal conductivity and conductivity of Sn63/Pb37 is similar, wettability, good mechanical properties, solder joints have enough mechanical strength and thermal aging resistance, compatible with existing welding equipment and process. The solder joints are easy to repair, low cost, and the selected materials can ensure adequate supply.

1, Sn-Ag-Cu system solder paste

This system contains two types of solder: Sn96.5Ag3.0Cu0.5 and Sn99Ag0.3Cu0.7, which are characterized by better mechanical properties, tensile strength, creep thermal properties and heat aging properties than Sn-Pb eutectic solder, and worse ductility than Sn/Pb eutectic solder. Its melting point is between 210 ℃ and 230℃.

Features:

(1) Good printing fluidity, precision printing can be completed on pads as low as 0.3mm spacing.

② Continuous printing, its viscosity change is very small, the steel net can operate long life, more than 8 hours will not dry, still maintain good printing effect.

(3) The original shape is still maintained for several hours after printing, basically without collapse, and the patch components will not produce deviation.

④ Has excellent welding performance, can be in different parts of the surface of the appropriate wettability.

(5) Can adapt to the requirements of different grades of welding equipment, no need to complete the welding in the oxygen-filled environment, in a wide range of reflow furnace temperature can still perform good weldability.

The welding residue is very small, the color is very light and has a high insulation resistance, the corrosion is very small, to achieve the requirements of free washing.

⑦ Excellent ICT test performance, no misjudgment.

2, SN-BI tin paste

This solder paste is characterized by low melting point (138℃) for those electronic components with poor heat resistance welding advantage, its preservation stability is good, wettability is quite excellent. Solder paste purchasing this system using special help tin solder paste and oxide content few spherical powder refined but become, excellence as continuous printing solutions, in addition, this system contains the help solder paste by solder paste, the low ionic activator system with high reliability, the residues after reflow small and high insulation resistance, High electrical stability and safety reliability after welding.