Laminated Structure of Multilayer PCBs

Solder Alloy Used:

• Composed of lead-free alloys, such as Sn-Cu (Tin-Copper) or Sn-Ag-Cu (Tin-Silver-Copper).
• Complies with Restriction of Hazardous Substances (RoHS) directives for environmental safety.

Typical Thickness:

• The solder coating thickness typically ranges from 1 μm to 40 μm.
• Thickness can vary depending on board design, feature density, process parameters, and the specific alloy used.

Cost:

• Lead-free HASL is considered one of the most economical PCB finishes.
• The process is cost-effective due to simple equipment requirements and fast throughput, making it suitable for prototypes and mass production.

IPC Standards Compliance:

• Generally conforms to IPC-6012 (for rigid PCBs) and IPC-6013 (for flexible and rigid-flex PCBs).
• These standards specify requirements for finish thickness, appearance, adhesion, and overall product quality.

Solderability:

• Provides good solderability for most through-hole and surface mount components.
• The finish is compatible with lead-free assembly processes, which operate at higher temperatures than leaded processes.

Surface Planarity:

• May result in an uneven surface due to the nature of the solder leveling method.
• Less suitable for fine-pitch surface-mount device (SMD) components or ball grid arrays (BGAs), which require excellent planarity for reliable solder connections.

Assembly Requirements:

• Requires higher reflow temperatures compared to leaded HASL due to the higher melting point of lead-free solder alloys.
• Special care must be taken during assembly, as repeated heating cycles may impact solderability.
• More attention is needed to avoid solder bridging or issues with uneven pads, especially for boards with high-density or fine-pitch features.

Shelf Life and Reliability:

• Offers moderate to good shelf life when compared to bare copper.
• May not be as corrosion-resistant as gold-based finishes but provides adequate protection during storage, transport, and assembly.

Environmental Impact:

• Lead-free HASL is environmentally friendly due to the absence of hazardous lead content.
• Supports compliance with global environmental regulations such as RoHS and WEEE.

Common Use Cases:

• Widely used for consumer electronics, industrial controls, automotive, and other applications where cost-efficiency and reasonable performance are priorities.
• Selected for general-purpose PCBs where ultra-flat surfaces or high-density features are not required.