Vapor Phase Soldering

Introduction to Vapor Phase Soldering

Vapor phase soldering, also known as condensation heating, is a direct contact process that occurs in a zone of heated, saturated vapor. The process utilizes the latent heat of vaporization when hot, saturated vapor condenses on a surface. This technology has been successfully adapted for mass reflow soldering, paint and polymer coating, and polymer fusing applications, providing precise temperature control in a clean, non-oxidizing, and non-flammable environment.

Process Principles and Methodology

The VPS process involves heating a special inert liquid to create a saturated vapor atmosphere. When the product requiring soldering is immersed in this atmosphere, the vapor contacts the product and releases its latent heat of vaporization during condensation. This results in highly efficient and uniform soldering across the entire product surface.

Figure 1: Vapor phase soldering method

Technical Advantages and Benefits

1. Superior Heat Transfer
   • Exceptionally high efficiency in heat transmission
   • Uniform heating regardless of component geometry
   • Independent of circuit assembly mass, color, or composition
2. Temperature Control
   • Precise temperature regulation through latent heat
   • Component temperature never exceeds vapor temperature
   • Lower processing temperatures compared to IR or hot air methods
3. Environmental Protection
   • Minimal oxidation of soldered sections
   • Clean, non-oxidizing atmosphere
   • Reduced contamination risk
4. Process Efficiency
   • Short processing times
   • Minimal thermal stress on packages
   • High reliability with reduced rework requirements

Limitations and Considerations

The primary disadvantage of VPS technology is:

• Higher operational costs compared to traditional methods

Comparison with Other Soldering Technologies

There are three types of commonly used production soldering stations:

1. Wave solder systems
2. Convection systems (Including three SMEMA classifications)
   • Class 1 IR (radiant dominant)
   • Class II IR (combination convection and IR)
   • Class III (convection dominant)
3. Vapor phase reflow (VPR) systems

While these systems share the basic function of heating boards above the solder's liquidous point, they differ in:

• Heating methodology
• Solder application timing and technique
• Temperature change rates
• Process control capabilities

Equipment Configuration

The standard VPS equipment configuration includes:

• Primary vapor phase chamber for batch reflow soldering
• Preheating system
• Cooling mechanism
• Secondary vapor phase for liquid containment