Technical requirements and printing characteristics of lead-free solder paste

Lead-free solder pasteThe technical requirements and printing characteristics?Lead-free solder paste must first be able to truly meet environmental protection requirements. Lead cannot be removed and new harmful or harmful substances will be added. In order to better ensure the forgeability of lead-free solder and the stability after soldering, many problems must be taken into account, such as the cost of customer responsibility. In conclusion, lead-free solder should meet the following requirements as much as possible:

　　First, the melting point of lead-free solder should be low and as close as possible63/37The carbide temperature of tin-aluminum alloy183℃. If the carbide temperature of the new product is only high183℃This should not be a problem, but lead-free solder has not yet been truly popularized and met the welding requirements. In addition, before developing and designing lead-free solders with low eutectic temperatures, the temperature difference in the molten section of the lead-free solder should be minimized as much as possible. That is, the temperature range between the solid heat wire neutral line and the high-performance liquid phase line should be reduced as much as possible, and the temperature of the solid heat wire neutral line should be at least150℃The high-performance liquidus temperature should be determined according to the actual application(Wave soldering machine solder tape:Less than265℃;Tin bar:375℃The following;Solder paste for surface mount welding:Less than250℃The temperature of the reflow soldering furnace is generally specified to be less than225~230℃.
　　Second, lead-free solder should have excellent lubricity. Generally speaking, the duration during which solder remains around the high-performance liquid phase line in a reflow soldering furnace is30-90The duration for which the solder pins and the surface layer of the circuit board substrate come into contact with the solder solution during the wave soldering machine is approximately seconds4Seconds. After applying lead-free solder, it is essential to ensure that the solder exhibits excellent lubrication performance during the above-mentioned time period to guarantee a high-quality actual soldering effect.
　　Thirdly, the electrical conductivity and thermal conductivity after welding should be close63/37Tin-aluminum alloy solder.
　　Fourth, the compressive strength, ductility, plasticity and stress relaxation resistance of spot welding should be similar to those of tin-aluminum alloy.
　　Fifth, try to control costs as much as possible;At present, it can also be adjusted in tin-aluminum alloy1.5~2This is an idealized price.
　　The packaging and printing characteristics of lead-free solder paste:
　　First, the packaging printing has good flipping and tin dropping properties, with a low interval0.3mmThe ink pad can Carry out exquisite packaging printing. In the continuous packaging printing process, the viscosity change of the ink pad is not significant, and the executability on the steel wire is long, exceeding12The printing pad does not dry out easily after a few hours, and the actual printing effect of the packaging is still very good. For the past few hours after printing, it has remained the same as before. Most of it has not collapsed and the patch elements have not deviated;
　　Second, excellent resistance to thermal and cold collapse. Because the viscosity is higher than averageSMTThe solder paste is low, and the high-temperature solder paste is relatively very prone to collapse. Moreover, the interfacial tension of the high-temperature solder paste during the melting process is higher than that of the traditional one63/37The solder paste is large, so if it collapses before melting and connects with other solder layers, the probability of bridging after reflow soldering is higher. Relay is one of the most common phenomena in the production and manufacturing of high-frequency tape drives. With the development trend of data high-frequency tape drives, more and more high-density designs have been developed, so good resistance to cold and hot collapse is of vital importance. Selecting the appropriate solder paste is an effective way to prevent relay, reduce rework, improve work efficiency and product stability.
　　Third, the viscosity change of high-temperature solder paste is small and its service life is long. The variation of viscosity can cause changes in the volume of packaging printing, especially during the printing process. Therefore, maintaining a relatively stable viscosity is crucial for ensuring the consistency of spot welding. In the vast majority of cases, when the viscosity of high-temperature solder paste increases, it will also decrease accordingly. For instance, after the solder paste dries, it basically loses its viscosity, which will cause Solder paste is released during the insertion process due to viscosity damage, thereby causing Solder leakage.
　　Fourth, high-temperature solder paste has excellent welding properties and can demonstrate appropriate lubricity at different positions;It can meet the requirements of different levels of welding machinery and equipment, and does not need to be welded in a nitrogen injection environment. It can still exhibit excellent welding properties within a wide range of reflow oven temperatures. "Temperature increase can be selected.-Two temperature control setting methods: "heat insulation and preservation" or "gradual temperature increase". After welding, there is very little residue, the color tone is very light, the grounding resistance is large, the printed circuit board is not corroded, and it can Consider the regulations on uncleanliness.

The printing characteristics of lead-free solder paste:

First, the printing has good rolling and tin dropping properties, and the spacing is as low as0.3A printing pad of millimeters can achieve exquisite printing. During the continuous printing process, the viscosity of the printing pad does not change much, and its operability on the steel screen is long, exceeding12The ink pad won't dry after a few hours and the printing effect is still very good. Several hours after printing, it still maintained its original shape, with basically no collapse occurring and the patch elements not shifting;

Second, good resistance to thermal collapse. Because the viscosity is higher than that of the ordinarySMTThe solder paste is low. High-temperature solder paste is relatively prone to collapse, and the surface tension of high-temperature solder paste during the melting process is higher than that of traditional ones63/37The solder paste is large, so if it collapses before melting and connects with other pads, the possibility of forming a bridge after reflow soldering is greater. Bridging is one of the most common problems in the production of high-frequency magnetic heads. With the development of digital high-frequency magnetic heads, more and more high-density designs have been developed. Therefore, good resistance to cold and hot collapse is particularly important. Choosing the appropriate solder paste is an important way to avoid bridging, reduce rework, and improve production efficiency and product reliability.

Third, the viscosity change of high-temperature solder paste is small and its service life is long. Changes in viscosity can cause variations in the print volume, especially during printing. Therefore, maintaining a relatively stable viscosity is crucial for ensuring the consistency of solder joints. In most cases, when the viscosity of high-temperature solder paste increases, it is accompanied by a decrease in viscosity. For instance, after the solder paste dries, it almost loses its viscosity, which will cause the solder paste to be pushed out during the insertion process due to the loss of viscosity, thereby resulting in solder leakage.

Iv.High-temperature lead-free solder pasteIt has excellent welding performance and can exhibit appropriate wettability in different parts;It can meet the requirements of welding equipment of different grades, does not need to complete welding in a nitrogen-filled environment, and still shows good welding performance within a wide temperature range of reflow ovens. "Heating up can be adopted.-There are two ways to set the furnace temperature: "heat preservation" or "gradual heating". After welding, there is very little residue, the color is very light, the insulation resistance is large, the printed circuit board does not corrode, and it can meet the requirement of no cleaning.

Shenzhen JJY has carried out mutually beneficial cooperation with electronic raw material producers. At the same time, it also produces solder wire, solder bar, solder paste and flux paste for other enterprises. With a rich variety of successful cases in the research and development of chemical raw materials, our overall strength has created a sales market that is of high quality and honest and trustworthy.