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Finishing coating Lead Free HASL

Lead Free HASL is a lead-free tinning method. This finishing coating is made from a combination of Sn96 or Sn100 alloys with Ag / CuO, Cu/Ni, Ag2/Ni and it fully meets all the requirements of the international RoHS directive.

The reasons for the popularity of lead-free condensation soldering method:

The efficient production process, the ease of production and low cost of raw materials are the initial reasons for the rapid development of this finishing coating.

In addition, it is worth noting the safety and high strength characteristics of a connection of the copper contacts of the areas, as well as the possibility of repeated thermal cycling.

— Excellent solderability.

— The finishing coating is easy and inexpensive to produce.

— Significant temperature range of heat treatment.

— The intermetallic compounds between copper contacts and solder.

— The durability of the original characteristics of components, regardless of special storage conditions and the additional protection.

— Ability during the process of soldering to combine with lead solders (the recommended material to combine with - FR-4 High Tg) and multiple temperature fluctuations.

The temperature of the lead-free coating LF HASL during the application: 260−270˚. In its turn, such a temperature regime can deform the printed circuit board and cause several coplanarity problems — heterogeneous thickness of application. However, it should be noted that the heterogeneity of the application of this finishing coating is much lower than that of HASL Pb/Sn.

This technology is not suitable for SMD/BGA components with a pitch of elements less than 20 mm. Otherwise, shortings are possible. In addition, during the application the vapors are exuded, which does not meet modern international requirements of the production process.

Feature: if the printed circuit boards are not subjected to soldering more than 2 times and/or the overall process temperature is not higher than acceptable, then LF HASL method does not damage FR-2, CEM-2 and CEM-1 laminates. Note that with increasing heat resistance, the probability of damaging the materials is reduced.

Processing stages:

— Purification of printed circuit boards and application of flux.
— The immersion of the board for a while in a recyclable solder bath. The most popular are vertical methods of immersion.
— Removal of excess solder residues using air knives (high temperature air flow) and flux.
— Drying and quality control of the printed circuit board.
Technology opportunities
Period of storage, months
Solderability quality
Multiple solderability
Thermal profile state when flowing solder
Not critical, but it requires the application of methods that ensure the preservation of gold thickness within 0.3 mm
Availability of gold welding process compatibility
Availability of aluminum welding process compatibility
Finishing coating thickness, μm
Optimum pitch of landing areas, mm
≥ 0,5
Process temperature characteristics, ˚С
Torsion, bending and dimensional stability problems
Complanarity state of landing areas
Surface cleanness state
Corrosion resistance index
Visual defects
Qualitative risks
The possibility to reduce the sizes of the holes
Solder reliability index
Compatibility with lead free methods
Index of the environmental damage, safety for the human body
Cost characteristics