PCB HASL and Lead-Free HASL Processes

HASL process

HASL (Hot Air Solder Leveling) is one of the most classic and cost-effective surface treatment processes in PCB manufacturing and plays an important role in the electronics manufacturing industry. This process involves covering the copper surface with a tin-lead alloy layer to provide reliable soldering performance and oxidation protection for PCBs.

1.1 Differences between HASL and lead-free HASL

HASL (Hot Air Solder Leveling) is one of the most classic and cost-effective surface treatment technologies in PCB-productie. This process coats copper surfaces with a tin-lead alloy layer to provide reliable solderability and oxidation resistance. With increasing environmental requirements, lead-free HASL has become the industry standard.

Material Composition Differences:

• Traditional HASL uses Sn63/Pb37 alloy (63% tin + 37% lead), melting point: 183°C
• Lead-free HASL primarily uses:
• SAC305 (96.5% tin + 3% silver + 0.5% copper), melting point: 217-220°C
• SnCu0.7 (99.3% tin + 0.7% copper), melting point: 227°C
• Pure tin (Sn100), melting point: 232°C

Process Characteristics Comparison:

Practical Performance Differences:

• Soldeerbaarheid:

• Leaded HASL offers better solder activity with shorter wetting time (1-2 sec)
• Lead-free HASL requires stronger flux and tighter temperature control

• Betrouwbaarheid:

• Leaded solder joints exhibit better thermal fatigue resistance (more temperature cycles)
• Lead-free solder joints maintain higher mechanical strength after long-term aging

• Process Window:

• Leaded HASL has a wider process window (±10°C)
• Lead-free HASL requires tighter temperature control (±3°C)

Professional Tip: Topfast optimizes lead-free HASL parameters to achieve >99.5% soldering yield while meeting IPC-6012 Class 3 standards.

1.2 Core HASL Process Flow

As a professional PCB manufacturer, Topfast employs fully automated HASL production lines with strict standardized processes:

1.2.1 Pre-Treatment Stage

• Chemical Cleaning:
• Acid cleaner (pH 2-3) removes copper oxides
• Temperature control: 40-50°C, duration: 2-3 min
• Micro-etching ensures surface roughness Ra 0.3-0.5μm
• Rinsing:
• Three-stage countercurrent rinsing (DI water resistivity >15MΩ·cm)
• Hot air drying (60-80°C)

1.2.2 Flux Application

• Application Methods:
• Foaming (traditional): Flux thickness 0.01-0.03mm
• Spray (advanced): More uniform, 30% less flux consumption
• Flux Types:
• No-clean rosin-based (ROH)
• Solid content: 8-12%, acid value: 35-45mgKOH/g

1.2.3 Hot Air Leveling Key Steps

• Preheating:

• Leaded: 130-140°C
• Lead-free: 150-160°C
• Duration: 60-90 sec

• Solder Dipping:

• Solder pot temperature:
  • Leaded: 210±5°C
  • Lead-free: 250±5°C
• Dwell time: 2-4 sec (±0.5 sec precision)
• Immersion depth: 3-5mm

• Hot Air Leveling:

• Air knife parameters:
  • Pressure: 0.3-0.5MPa
  • Temperature: 300-350°C
  • Angle: 4° downward tilt
  • Air velocity: 20-30m/s
• Processing time: 1-2 sec

• Cooling:

• Forced air cooling (rate: 2-3°C/sec)
• Final temperature <60°C

1.2.4 Quality Inspection

• Online AOI (100% coverage):
• Solder thickness inspection (1-40μm)
• Surface defect detection (solder balls, exposed copper, etc.)
• Sampling Tests:
• Solderability test (245°C, 3 sec)
• Adhesion test (tape method)

Technological Breakthrough: Topfast’s nitrogen-protected lead-free HASL process reduces solder oxidation from 5% to <1.5%, significantly improving soldering yield.

1.3 Process Advantages and Limitations

Voordelen

• Kostenefficiëntie:

• Low equipment investment (~1/3 of ENIG)
• Significant material cost savings (40-60% cheaper than ENIG)

• Solder Reliability:

• Withstands >3 reflow cycles (peak 260°C)
• High joint tensile strength (leaded: 50-60MPa; lead-free: 55-65MPa)

• Wide Applicability:

• Suitable for various pad sizes (min. 0.5mm pitch)
• Compatible with through-hole and SMT processes

• Storage Performance:

• 12-month shelf life (RH <60%)
• Excellent oxidation resistance (48-hour salt spray test)

Beperkingen

• Fine-Pitch Restrictions:

• Not suitable for <0.4mm pitch BGA/QFN components
• Solder bridging risk for fine-pitch designs

• Planarity Issues:

• Surface unevenness: 15-25μm (affects HDI assembly)
• Thickness variation up to 20μm between large/small pads

• Thermal Stress:

• High-temp process (especially lead-free) may affect high-Tg materials
• Higher warpage risk for thin boards (<0.8mm)

• Environmental Considerations:

• Leaded HASL non-RoHS compliant
• Lead-free HASL consumes more energy (30-50°C higher temperatures)

Need professional HASL support? Contact Topfast engineers voor oplossingen op maat

ENIG (Electroless Nickel Immersion Gold) Process

2.1 Process Principles

ENIG forms a composite protective layer through electroless nickel plating and immersion gold:

• Nickel layer: 3-6μm (7-9% phosphorus)
• Gold layer: 0.05-0.1μm

Belangrijkste parameters:

• Nickel bath temp: 85-90°C
• Plating rate: 15-20μm/h
• Gold bath temp: 80-85°C
• pH: Nickel bath 4.5-5.0, Gold bath 5.5-6.5

2.2 Advantages

• Superb Flatness (Ra<0.1μm):

• Ideal for <0.3mm pitch BGA/CSP
• Pad coplanarity <5μm/m

• Oxidation Resistance:

• 18-month shelf life
• J-STD-003B Class 3 certified

• Electrical Conductivity:

• Gold resistivity: 2.44μΩ·cm
• Contact resistance <10mΩ

2.3 Challenges

• Black Pad Issue:

• Causes: Nickel over-etching or abnormal phosphorus content
• Solution: Topfast’s patented passivation reduces black pad rate to <0.1%

• Cost Factors:

• High material costs (gold price volatility)
• Complex process (8-10 steps)

• Solder Joint Strength:

• Brittle Ni-Au IMC layer
• Tensile strength ~40-45MPa

Topfast’s ENIG achieves ±10% thickness uniformity, surpassing industry ±15% standards.

OSP (organisch soldeerbaarheidsbewaarmiddel)

3.1 Process Principles

OSP forms a 0.2-0.5μm organic protective film on bare copper, containing:

• Benzotriazole compounds
• Imidazole compounds
• Carboxylic acids

Processtroom:

1. Acid clean (5% H2SO4, 2min)
2. Micro-etch (Na2S2O8, remove 1-2μm copper)
3. OSP treatment (40-50°C, 1-2min)
4. Drying (60-80°C hot air)

3.2 Advantages

• Kosteneffectief:

• 60% cheaper than HASL
• Low equipment investment (~1/5 of ENIG)

• Signaalintegriteit:

• Stable dielectric constant (ΔDk <0.02)
• Ideal for high-frequency applications (>10GHz)

• Eco-Friendly:

• No heavy metals
• Simplified wastewater treatment

3.3 Limitations

• Solderability Window:

• Must use within 24 hours of opening
• Only suitable for 1 reflow cycle (yield drops 30% for second reflow)

• Inspection Difficulties:

• Hard to measure film thickness optically
• Requires special ICT treatment

• Storage Conditions:

• Vacuum packaging required (RH <30%)
• Storage temp: 15-30°C

Topfast’s enhanced OSP extends shelf life from 3 to 6 months and withstands 2 reflow cycles.

Process Selection Guide

4.1 Comparison

4.2 Recommendations

• Consumentenelektronica:

• Lead-free HASL (best cost-performance)
• Control solder paste volume for fine-pitch components

• HDI-borden:

• ENIG (superior flatness)
• Strict nickel quality control

• PCB's met hoge snelheid:

• OSP/ENIG (better signal integrity)
• Avoid HASL’s uneven surface

• Prototyping:

• OSP (fastest turnaround)
• Ensure timely assembly

4.3 Topfast Capabilities

Complete surface finish solutions:

• 20 automated HASL lines (500,000㎡/month)
• 10 ENIG lines (±8% thickness uniformity)
• 5 OSP lines (nano-enhanced available)
• 100% inline inspection (AOI+SPI)

Download PCB Surface Finish Selection Guide