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Precautions for lead-free dip soldering and lead-free wave soldering

Date: 2014/12/13 10:32

1) The temperature of the tin furnace during lead-free dip soldering should generally be set to ≤300oC. The biggest problem of lead-free dip soldering is the removal of Cu-Sn intermetallic compounds. This aspect will bring unexpected difficulties compared with Sn-Pb solder. No matter it is a copper wire, a printed circuit board, or a transformer, such as a dipping process, the copper thereon will dissolve into molten solder in a tin furnace to varying degrees. Intermetallic compounds are easily formed between Cu and Sn, generally Cu6Sn5, and the melting point of the compound is above 500oC, so it exists in solid form. The density of traditional Sn63-Pb37 alloy is 8.80g / cm3, while the density of Cu6Sn5 is 8.28g / cm3. Therefore, the compound will float on the surface of the molten solder in the leaded process, which is relatively easy to remove. However, in the lead-free process, since the density of lead-free solder is generally about 7.40 g / cm3, its density is smaller than that of Cu-Sn intermetallic compounds, so Cu-Sn intermetallic compounds will sink to the bottom of the tin furnace and Could not be cleared. These Cu-Sn intermetallic compounds sunk in the bottom of the tin furnace will adhere to the accessories at the bottom of the device, causing problems such as poor heat transfer. Therefore, for the lead-free dip soldering process, regular furnace cleaning is a necessity. According to the production density of customers, we recommend that the furnace be cleaned once an month on average.

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2) Another problem of dip soldering process is the problem of flux evaporation. The carrier of the liquid flux is an organic alcohol substance, which is easy to volatilize and cause the specific gravity of the flux to increase, that is, the relative percentage of the active ingredient in the flux increases. This will cause many problems such as increased surface residue after welding. Therefore, it is necessary to strictly control the specific gravity of the flux in the dip soldering process. It is recommended to use a hydrometer to test once every day. If it is found that the specific gravity exceeds the data index of the flux supplier, the specific gravity is adjusted to a standard value by adding a thinner.

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Lead-free wave soldering

1) In the lead-free wave soldering process, two basic characteristics must be noticed at all times: lead-free solder has a higher melting point, and therefore requires a higher soldering temperature; because lead-free solder has poor wettability, it needs to be matched with it Lead-free special flux.

2) At present, lead-free wave soldering equipment generally uses a spray method to apply flux. The spray parameter is adjusted so that the flux can be evenly distributed on the surface of the printed circuit board without dripping. On the premise of meeting this requirement, the spray pressure should not be too high. At the same time, well-designed wave soldering equipment generally reduces the volatility of the solvent in the liquid flux to a small level, but you should also remind yourself to regularly check the proportion of the liquid flux. If it is too high, add diluent in time to adjust.

3) The tin furnace temperature should be set to 255-270oC during lead-free wave soldering, generally 260oC. At the same time, in view of the corrosiveness of the high-tin solder described in 5.3, titanium alloys should be used in the parts of the tin furnace that are often in contact with the molten solder.

4) The preheating temperature should be increased during lead-free wave soldering. We recommend two sets of data, one is the preheating temperature of 150oC, and the other is the preheating temperature of 120oC. In general, we recommend the former. At the same time, lead-free wave soldering equipment should have 2 or more preheating temperature zones, and the temperature can be set to the same value.


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