Temperature selection of lead-free alloy for the h

2022-07-27
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Temperature selection of lead-free alloys for wave soldering

preface

for a long time, wetting balance test has been an effective laboratory method to evaluate the wettability of solders. Wetting balance test is required for three kinds of materials, namely substrate, flux and solder. The base material can be a metal area on the surface of the printed board, or a lead or terminal of an electronic component. The wetting balance test is used to evaluate the weldability of metal surfaces. The test procedure is detailed in IPC  J  002 and IPC  J  003. Wetting balance test is also used as a screening tool to evaluate the wetting effect of flux

in recent years, wetting balance test has been used to evaluate the wettability of various alloy solders, especially the wettability of lead-free alloy solders. The wetting balance test method is a part of the comprehensive study on reflow soldering and wave soldering of lead-free solder. The purpose of wetting balance test is to evaluate the adaptability, weldability and welding quality of materials. The research contents include the main proportion of alloy, flux and solder paste, the appearance of plug-in board, surface installation, through holecomponents and specially designed test board. In this paper, the wetting balance tester is selected to measure the temperature suitable for various lead-free alloy solders in the metallographic research of wave soldering, which provides a new product selection and solution for customers in the medical industry

wetting balance test method

1 alloy solder

evaluate the following five kinds of lead-free alloy solder, including tin silver and silver copper binary alloy solder, tin silver copper ternary alloy solder, tin silver copper bismuth and tin silver copper antimony quaternary alloy solder, as well as eutectic tin lead solder. See Table 1 for the assessed special alloy and its melting temperature range. Table 1 alloy solder and melting temperature range

alloy melting temperature range tin 63/lead 37183 ℃ tin 99.3/copper 0.7227 ℃ tin 96.5/silver 3.5221 ℃ tin 95.5/silver 4/copper 0.5217 ℃ ~ 218 ℃ tin 96/silver 2.5/bismuth 1/copper 0.5214 ℃ ~ 218 ℃ tin 96.2 silver 2.5/antimony 0.5/copper 0.8210 ℃ ~ 216 ℃

2 test preparation

25.4mm for wetting balance test of substrate × 12.7mm × 0.13MM copper attached test plate. The attached test board shall meet the HA conditions in iso1634cu  ETP. The attached test plate shall be pre cleaned according to the following steps:

remove oil in boiling isopropanol

deoxidize with copper surface treatment agent

wash with deionized water

finally, clean with isopropyl alcohol

the wetting balance test shall be carried out on the newly cleaned attached test plate which has been oxidized at 100 ℃ for 1 hour

③ add all the pendulums to the

3 wetting balance test

conduct the solder wetting test with the wetting tester, and the solder groove of the tester shall be filled with each alloy tested in sequence. Immerse the attached test plate in the no clean flux with low curing point to a depth of 2.54mm, then preheat the attached test plate at 2.54mm above the solder bath for 5min, and then immerse the attached test plate at 2.54mm above the solder bath for 5S. The immersion and removal speed is 25.4mm/s. No matter whether the oxidized copper attached test board or the non oxidized copper attached test board uses flux, the test is conducted within the solder temperature range, and 15 attached test boards are used for each solder alloy, solder temperature and surface condition of the attached test board

test results

record 2 measurement results for each wetting test, i.e. wetting time and wetting force. The wetting balance test results obtained from this study are shown in Figures 1 to 4. Each point in the figure represents the average of the measurement data of 15 attached test plates

Fig. 1 wetting time between each alloy solder and copper oxide when using flux Fig. 2 wetting force between each alloy solder and copper oxide when using flux Fig. 3 wetting time between each alloy solder and copper oxide when using flux Fig. 4 wetting force between each alloy solder and copper oxide when using flux Fig. 1: tin 63/lead 37 alloy

2: tin 95.5/silver 4/copper 0.5 alloy

3: tin 99.3/copper 0.7 Gold

4 means tin 96.5/silver 3.5 alloy

5 means tin 96/silver 2.5/bismuth 1/copper 0.5 alloy

6 means the root of tin 96.2/Silver 2 salad plant 5/antimony 0.5/copper 0.8 alloy

figures 1 and 2 show the results of wetting time and wetting force of each test alloy and flux when using non oxidized copper. Figures 3 and 4 show the results of wetting time and wetting force of each test alloy and flux when oxidized copper is used

the results show that: (1) when using low solidifying point, no clear rosin flux, the temperature of near sighted lead-free alloy solder appears at 271 ℃. When using non oxidized copper and low solidifying point flux, the wetting time is shortened as the lead-free alloy temperature reaches 271 ℃, and then the wetting reaches equilibrium or the wetting force increases slightly with the increase of temperature. Similarly, when the temperature reaches 271 ℃, the wetting force increases, then reaches equilibrium or decreases slightly with the increase of temperature. (2) The wetting time of Sn Ag binary alloy and Sn Ag Cu ternary alloy is faster and the wetting ability is stronger than that of 4-ary alloy and Sn Pb alloy; (3) The minimum temperature for tin copper alloy to meet the requirements of complete wetting is 260 ℃; (4) The minimum temperature for the 4-element alloy to meet the requirements of complete wetting is 249 ℃; (5) The minimum test temperature for complete wetting of Sn Ag and Sn Ag Cu alloys is 232 ℃; ⑥ The minimum test temperature for tin lead alloys to achieve complete wetting is the same as that for tin silver and tin silver copper alloys. When using oxidized copper and low solidifying point flux, the results of different alloys are very similar. With oxidized copper substrate, the solder temperature of 271 ℃ can usually obtain better results than at lower temperature. However, some alloys have better edge effect at the maximum test temperature of 277 ℃. When using non oxidized copper, the wetting time of tin silver binary alloy and tin silver copper ternary alloy is slightly faster and the wetting force is slightly stronger than that of oxidized copper. This trend is just opposite to that of quaternary alloy and tin lead alloy, that is, the wetting effect of oxidized copper is better than that of non oxidized copper

conclusion

the results of wetting balance test show that windformxt2.0 is a top-level laser sintering material when using low curing point non cleaning rosin flux to evaluate the temperature of lead-free alloy solder. At 271 ℃, it is close to the temperature of lead-free alloy solder. Tin silver alloy, tin copper alloy and tin silver copper alloy generally have short wetting time and strong wetting power; The adaptability and solder temperature of each lead-free alloy solder must be verified in the actual wave soldering process of double-sided metallized orifice plates and surface mounted electronic component printed boards. (end)

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