Wave soldering temperature

TABLE 6 Solder Alloy Properties Affecting Stress Levels in Through-Hole Joints During Cooling from the Wave Soldering Temperature... 

Most commercial wave soldering machines have a preheating section before the PCB or assembly is immersed into the solder wave, the thermal shock is reduced As the ambient temperature has already been raised before the solder wave, the thermal gradient in the reed switch seal is reduced. 

In general, standard industrial cyanoacrylates do not operate effectively above 180°F (see Fig. 4). However, the new allyl types of cyanoacrylates can operate as high as 480°F before the bond loses sufficient strength to be operationally effective (see Table 2). Allyl cyanoacrylates for metal-bonding applications have proven effective in wave solder and under-hood (automotive) applications. In Fig. 4, bonded assemblies are cured at room temperature for 24 h. The assemblies are heated for 2 h and tested hot. 

Pin in paste (PIP) technology, also know as alternate assembly and reflow technology (AART) by Universal Instruments and others, allow the use of THT parts with solder paste and reflow soldering. Paste is deposited onto the board at through-hole locations, the leads of a THT part are placed through the paste, and at the conclusion of the placement process the board and components are reflowed. The two major concerns with the use of the PIP process are the deposition of an adequate volume of solder paste and the use of THT components whose body can withstand reflow soldering temperatures. In the wave solder process, only component leads were raised to soldering temperatures, but in the reflow process the entire part must withstand the process temperatures. 

Glass fibers and inert mineral fillers can be used to provide additional rigidity, and it has been shown that reinforcements may be needed to prevent warpage during high-temperature wave soldering. 

Solder Float Resistance. This test addresses the thermal resistance of the laminate material floating on the solder bath. Becanse this method subjects the sample to a thermal gradient across the z-axis of the material similar to an actual wave solder operation, the resnlts of this test are particnlarly important and—as mentioned previously—either solder pot temperatures or exposure times should be increased if the laminates are intended for use in lead-free assembly processes. 

Immersion tin dissolves very quickly into SMT and wave solder. The tin may not melt (m.p. 232°C) but dissolves into the liquefied solder readily. Even before soldering, the immersion tin begins to form intermetallics with the copper beneath. In fact, with extended storage, the tin may be completely consumed by intermetallics before soldering. At soldering temperatures, the copper-tin intermetallics form at much higher rates. Areas of the PCB exposed to the assembly temperatures, but not soldered, will form thicker and thicker intermetallic layers until the pure tin is consumed. 

The impact of Pb-free technology on wave soldering has largely occurred in the equipment performance. It has been determined that the same solder bath temperatures that are used for Sn-Pb processes (250 to 270°C) are suitable for the Sn-Ag-XCu Pb-free alloys. Therefore, excessive dross formation and flux residue removal have not become a significant problem during equipment operation. The lack of shiny fillets with the Sn-Ag-XCu alloys has been addressed by modified alloys having Ni and Ge additions that alter the solidification process, which leads to shinier fillet surfaces. 

Zinc Solders. Zinc (Zn) alloys, favored by some Japanese companies, oxidize rapidly. Solder paste shelf-life has been an issue even when these alloys are refrigerated at very low temperatures. Dross formation in wave soldering has also been problematic. Zn alloys are also known to have some corrosion problems. 

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