Weak current College】 【lead-free solder and characteristic】.

<br> <br> And temperature, mechanical, creep, fatigue characteristics, the melting temperature point is the most important characteristics of solder. Table 4 provides now can buy to the list of lead-free solder. <br> Table 4, lead .-free solder and its characteristics <br> The chemical composition of lead-free solder <br> Melting range <br> Description <br> <br> 48Sn/52In <br> 118 ° C eutectic <br> Low melting point, expensive ., strength, low <br> <br> 42Sn/58Bi <br> 138 ° C eutectic <br> Has developed, Bi of concern <br> 91Sn/9Zn <br> 199 ° C eutectic <br> Multiple, potentially corrosive slag .<br> <br> 93.5Sn/3Sb/2Bi/1.5Cu <br> 218 ° C eutectic <br> High strength, good temperature fatigue properties <br> <br> 95.5Sn/3.5Ag/1Zn <br> 218 ~ .221 ° C <br> High strength, good temperature fatigue properties <br> <br> 99.3Sn/0.7Cu <br> 227 ° C <br> High strength, high melting point <br> <br> 95Sn/5Sb <br .> 232 ~ 240 ° C <br> Good shear strength and temperature fatigue properties <br> <br> 65Sn/25Ag/10Sb <br> 233 ° C <br> Motorola patent, high strength <br> <br> 97Sn/2Cu ./ 0.8Sb/0.2Ag <br> 226 ~ 228 ° C <br> High melting point <br> <br> 96.5Sn/3.5Ag <br> 221 ° C eutectic <br> High strength, high melting point <br> .<br> It should be noted that the lead-free solder the chemical composition is also optimized to achieve the desired characteristics. Table 4 in the chemical composition of solder may commercially purchased in solder has slightly different. For example, table 5 shows some from .different vendors purchase of solder brand. <br> Table 5, different vendor's lead-free solder <br> Solder name <br> Chemical composition <br> Melting point <br> Description <br> <br> Indalloy22777.2Sn/20In / .2.8Ag187 ° C potential In / Pb incompatibility, requirements on PCB pads and components-pin lead-free plating <br> AlloyH84.5Sn/7.5Bi/5Cu/2Ag212 ° C liquid temperature is too high, the requirements above 260 ° C soldering .temperature <br> Tin/Zinc/Indium81Sn/9Zn/10In178 ° C potential In / Pb incompatibility, requirements on PCB pads and components-pin lead-free plating <br> Castin96.2Sn/2.5Ag/0.8Cu/0.55Sb215 ° C .liquid temperature is too high, the requirements above 260 ° C soldering temperature <br> Tin/Silver/Copper93.6Sn/4.7Ag/1.7Cu217 ° C liquid temperature is too high, the requirements above 260 ° C soldering temperature <br> Contains .a high amount of Indium (In)-free solder (such as table 5 in the first alloy) have the potential of indium and lead not compatibility, if the Board and component pins on the lead. In order to get the real lead-free .process, if you use the Indium alloys, it may be necessary in the PCB use lead-free surface treatment. Industry is focusing on the development of alternative of plating layer. For example the AlphaLevel AlphaMetal Flash silver plating, and Motorola's on board and component .pins of Tin / bi plating. <br> From table 4 we can see that lead-free solder to not than tin / lead eutectic alloy melting temperature is much lower, not higher. As shown in table 5 are mostly high temperature lead-free .solder. When using the low-temperature solder, require special flux because standard flux may have no activity at low temperatures. And low-temperature solder related another temperature that is due to the time the eutectic temperatures, lower liquidity caused by the reduced wetting. .<br> Low temperature applications, indium solder is accepted. Some companies are using a 52In/48Sn of Indium solder because its better rework / repair features. Because the melting point of the alloy in 118 ° C (221 ° F), rework is .at a low temperature, the temperature generally do not cause damage. If the printed circuit board is gold-plated anti oxidation, indium solder can be used to prevent the loss of gold. <br> Another low melting point of lead-free solder is .58Bi/42Sn. If we look at Sn / Bi alloy metallography figure, will find its melting point in 138 ° C. BI for welding alloys to meet the low welding temperature, but the alloy general display of liquefaction characteristics on a business trip. < .br> Table 4 lists the many other alloys, than tin / lead eutectic 183 ° C of the melting point is much higher. Such as high temperature, zinc / lead-free solder Tin melting point to 198 ° C. <br> High melting .point solder will and now widespread use of substrate material, such as fusing FR-4, not. In addition, rework had to adopt high-temperature, will significantly increase the likelihood of damage to the Board. <br> There is also no mixed .-type lead-free solder alternatives, although some vendors make their solder described as "almost-mixed in." Even these requirements rework soldering iron temperature up to 400 ° C (750 ° F), which in some aspects of the application is a .too high a temperature, the temperature may cause potential damage. <br> Also, in the wave soldering of high melting point solder used in one of the key issues is to increase the capacitance of the possibility of rupture. Soldering temperature needs to be maintained .at approximately 230 ~ 245 ° C, higher than tin / lead solder melting point approximately 45 ~ 65 ° C. A melting point 220 ° C lead-free solder, requested 265 ~ 280 ° C temperature of soldering, which increases the warming and the .temperature difference between the wave, has increased the possibility of rupture of capacitance. <br> In General, almost all of the lead-free solder than tin / lead eutectic wetting performance difference (spread) That caused bad leg. In order to improve the .wetting performance, require special flux **. Lead-free solder fatigue characteristics are not very good, though in a study, using high-temperature 95.6Sn/3.5Ag (table IV final alloy) temperature cycle, no observation to the welding point integrity .of degradation. <br> Ideal solder melting point should be approximately 180 ° C, this return temperature 210 ~ 230 ° C, wave soldering furnace temperature to 235 ~ 245 ° C, hand soldering temperature of 345 ~ 400 ° C (650-700 .° F). Only very skilled operator can operate higher hand soldering temperature and avoid temperature damage. <br> Electronic Industries Association (IPC) standards, J-STD-006, provides detailed tin / lead or lead-free solder in the list. .However, no lead-free solder was designated as mixed-eutectic tin / lead substitute products. Industries are also looking for a real alternative to eutectic tin / lead in lead-free solder correctly. This is an industry must meet the challenge..