How to ensure the quality of lead-free wave soldering

    According to the EU's RoHS Directive (European Parliament and European Council on the restriction of electrical and electronic equipment, the use of certain Hazardous Substances Act), requiring from 1 July 2006 on the market in the European Union banned the sale of 6 containing harmful lead material

Electrical and electronic equipment, known as the  "green manufacturing" lead-free process is an irreversible trend.
wire cable trays, cable management systems, basket cable tray
    Currently, many Chinese manufacturers of electronic products are now actively lead solder from a large number of transition to lead-free solder testing. Experience shows that to improve the quality of lead-free wave soldering from equipment, materials, technology, and many other Canadian

To consider.

    Lead-free wave soldering of the cost factors

    Widely used in wave soldering is lead-free solder alloy SnAgCu solder it with the traditional SnPb solder than the melting point of solder and soldering temperature is much higher, see Table 1.

    Table 1 lead-free solder and leaded solder comparison of welding temperature

    Welding temperature melting point solder alloy

    Sn63Pb37183 ℃ 240-250 ℃

    Sn96.5Ag3.0Cu0.5217 ℃ 250-260 ℃

    Lead-free solder Sn content is much higher than those with lead solder, lead-free solder is more easily oxidized therefore,  produce more dross (SnO2), a large number of tin slag not only affect the quality of lead-free wave soldering, and generated a lot of waste.

    Typically, lead-free solder is 3-4 times the cost of lead solder. Assume that the factory produced three shifts of 15-30 kg of lead-free solder dross, the cost could reach RMB 3600-7200 yuan / day, a year is 100-200 million yuan.

    How to reduce lead-free wave soldering in the future a large number of expensive dross it? One effective method is introduced in the wave soldering technology a "full nitrogen tunnel protection technology", shown in Figure 1. That in the wave soldering process, including the long

Preheat zone and the wave of the tunnel areas are protected with a closed nitrogen. Very low oxygen concentration in the welding environment.

    Figure 2 shows that the nitrogen in the tunnel environment, the generation of dross rate has dropped by about 80%, so savings can be up to a year to 80-160 million yuan.

    Nitrogen technology can improve the whole quality of welding

    Nitrogen technology not only reduces the full operating costs, on the welding quality has greatly improved. As lead-free wave soldering in the surface tension of the liquid than the tin-lead solder large, less liquid, less invasive capacity, and therefore the peak through-hole components

Welding, multi-layer printed circuit board through  v holes in the lead-free solder fill and poor climbing ability, directly affect the solder joint strength and reliability.

    Large number of experiments show that the whole charge in the nitrogen environment, can reduce the lead-free solder liquid surface tension, improve mobility and invasive ability, it can improve the multi-layer PCB holes to climb in the capacity of lead-free solder. (Figure 3 holes

Metallographic section, the experiment shows the whole nitrogen in the environment climb through holes in the solder height is much higher than the atmospheric environment)

    Above reasons, lead-free wave soldering, solder bridging between adjacent solder joint defects than leaded wave soldering is much higher, and in the nitrogen environment throughout the welding joints can be greatly reduced bridging defects. Figure 4, Figure 5.

    Wave soldering process for through-hole components in addition to welding, but also widely used for soldering surface mount components.

The typical process for the dispensing patch → → → curing adhesive flip board (component side down) → wave soldering.

    OSP board PCB is used, also known as bare copper, bare copper pad coated with a thin layer of transparent organic protection layer. The board of the PCB with HASL pad compared with a good flatness is very suitable for fine pitch surface mount element

Device assembly, compared with nickel and gold plate cheap economy. But the board's pads easily oxidized, poor solderability.

    Most manufacturers of electronic products in  the cleaning process for the abolition of cumbersome and expensive cleaning equipment, commonly used no-clean process, that is, use no-clean flux. No-clean flux due to low activity, once the PCB pad oxide, weldability

Reduction will not be welded. Thus to obtain no-clean flux and bare copper lead-free wave soldering quality is very difficult. The solder joint defects are often exposed copper pads as shown in Figure 6. Experience shows that exposed copper pad to eliminate defects, not

Wave soldering machine tin bath only to nitrogen, and nitrogen in the preheat zone also, the entire nitrogen tunnel wave soldering technology to solve this problem. After welding is not exposed copper pads as shown in Figure 7.