Lead-free soldering equipment

The thermal performance is improved without any changes to existing processing equipment, such as molding machines, dies, molds, or extruders. The compositions can also be molded into various shapes and forms, such as connectors, circuit boards, pipes, rods, films, sheets, and bearings, which render them useful in electrical applications that might result in contact with lead-free solder [86]. 

If adhesiveless laminates are used as the major materials, high temperatures can be used with lead-free soldering. In the case of SMT assembling, the flexible circuit should be fixed on a carrier frame. This allows it to be processed by the same mounting and soldering equipment as used for rigid boards. 

Processes, Equipment, and Quality For Lead-Free Soldering... 

Rework for lead-free solders has been found to be more difficult, because the lead-free solder alloys typically do not wet or wick as easily as the Sn-Pb solder due to their difference in wettability. This can be easily seen with QFP packages. In spite of these differences, successful rework methods (both manual and semi-automatic) have been developed (Ref 74-75) with lead-free solders (Sn-Ag-Cu, or Sn-Ag), for many different types of components. Most of the rework equipment for tin-lead can still be used for lead-free solder. For area array packages, it is helpful to use a rework system with split vision and temperature profiling features. The soldering parameters must be adjusted to accommodate the higher melting temperature and reduced wettability of the lead-free solder. The other precautions for tin-lead rework (such as board baking) still apply to lead-free rework. 

The lead-free transition will have some impact on the stencil printing process. Printability of solder paste depends on flux formulation, but not for all alloy types. Experience has proven that there are no differences when printing lead-free solder pastes than when printing tin/lead solder pastes. Formal testing has verified that the printed volume of several lead-free solder pastes and tin/lead solder pastes were the same statistically when using the same stendl, printing equipment and boards (Figure 2). 

Lower-budget operations and/or those that have a relatively new wave machine that is not depreciated fully may want to continue using their current wave-soldering equipment after lead-free soldering has been implemented. However, if you are using an SnAgCu alloy, baffles, pumps, and... 

In this test, multiple, stainless steel stencils and PCBs were prepared with the latest lead-free solder pastes available. After an hour of drying time, each stencil, in conjunction with a misprinted board, was cleaned at room temperature in spray-in-air equipment for three to six minutes (Table 2). Subsequently, cleaning tests were repeated at room temperature in ultrasonic equipment. Test substrates cleaned were visually inspected under a microscope (lOx) and tested for solder-paste residues. It was shown that all tested cleaning agents removed all lead-free solder pastes (Table 3). Differences were observed in the cleaning times for the different cleaning applications. 

Directive 2002/95/EC Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment (RoHS) requires the components to be free of toxic substances, with only a few exceptions. Only lead-free solder can be used. Lead-free solders generally have higher melting points, so soldering operations have to be hotter and the components correspondingly temperature-resistant. 

Accommodating the heating profiles of lead-free solders will require that some reflow and wave soldering equipment be modified or reconfigured. 

Reflow equipment utilized for lead-free PCB assemblies should be flexible, especially in the ability to manipulate and control heating and cooling rates, because temperature control is critical. In general, lead-free soldering suffers from a lack of standardization [53]. 

Many North American companies are concerned that lead-free components and assemblies will not meet the reliability or functionality requirements necessary for high-end equipment supplied to banks, air traffic control systems, web-based businesses, and other mission-critical applications. Accordingly, manufacturers of aerospace and military electronics have no plans to introduce lead-free solders. There are too many reliability concerns to utilize lead-free solder materials in high-reliability equipment related to the mechanical characteristics of the materials themselves and the effects of high temperatures to process them. The effect of new and modified intermetallic compound phases within solder joints and at the interfaces is yet an additional concern, and there are many more. 

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