What does PCB manufacturer tell you about PCB board tin spraying process?

What does PCB manufacturer tell you about PCB board tin spraying process?

The common production processes in PCB factories include rosin OSP, gold deposition, electroplating, carbon oil, nickel plating, and tin spraying. Today, let's talk about PCB tin spraying HAL

Hot Air Solder Leveling (HASL) is a common method for surface treatment of printed circuit boards (PCBs), mainly used to coat a layer of tin lead or lead-free tin alloy on copper pads to improve soldering performance and oxidation resistance. The following is a detailed introduction to the tin spraying process:

1. Purpose of tin spraying process

Protect copper pads: prevent oxidation of the copper layer and ensure long-term solderability.

Improve welding performance: The tin layer provides good wettability for subsequent component welding.

Low cost: Compared to other surface treatments such as immersion gold and silver, the tin spraying process has a high cost-effectiveness.

2. Tin spraying process flow

pretreatment

Clean copper surface: Remove oxides and contaminants from copper pads through chemical cleaning.

Micro etching: Use micro etching solution (such as sodium persulfate) to roughen the copper surface and enhance the adhesion of the tin layer.

Coating flux

Spray soldering flux (usually rosin type) on the surface of copper to prevent oxidation and promote wetting of tin.

Tin immersion

Immerse the PCB into a molten tin furnace (tin lead alloy or lead-free tin, such as Sn Cu, Sn Ag Cu) at a temperature of approximately 250 ° C~280 ° C.

Hot air leveling (HASL)

Use high-temperature hot air (hot air knife) to blow the surface, remove excess tin material, and make the tin layer uniform and flat.

Cooling and cleaning

Quickly cool and solidify the tin layer, and clean the residual flux with clean water or solvent.

test

Check the thickness (usually 1-3 μ m), uniformity, and presence of defects such as solder beads and bridging of the tin layer.

3. Classification of tin spraying process

(1) Lead spray tin (Sn Pb HASL)

Ingredients: Tin (63%)+Lead (37%), with a melting point of approximately 183 ° C.

Advantages: Good welding performance, low cost, mature process.

Disadvantages: Contains lead, does not meet environmental requirements (such as RoHS), and is gradually being phased out.

(2) Lead Free HASL

Composition: Tin (Sn) as the main component, with added silver (Ag), copper (Cu), etc. (such as Sn96.5-Ag3-Cu0.5).

Advantages: Environmental protection, compliant with RoHS directive.

Disadvantages: High melting point (about 217 ° C~227 ° C), possibly rough tin layer, slightly higher welding difficulty.