The Tin Plating Process: A Step-by-Step Guide

Perhaps the biggest reason is that tin plating — or “tinning” — is an extremely cost-effective process. Because tin is so readily available, it is much less expensive than pricier metals such as gold, platinum or palladium.

 

Author: Anna

The Benefits of Tin in the Electroplating Process

 

Perhaps the biggest reason is that tin plating — or “tinning” — is an extremely cost-effective process. Because tin is so readily available, it is much less expensive than pricier metals such as gold, platinum or palladium. It also provides excellent solderability and superior corrosion protection.

 

Tin plating can achieve a whitish-gray color, ideal for a dull or matte finish, or a shiny metallic look for those seeking more luster. Additionally, tin offers a reasonable level of conductivity, making it suitable for manufacturing various electronic components. Importantly, tin is FDA approved for use in the food service industry.

 

Industries That Utilize Tin Plating

 

These benefits make tin the metal of choice for plating applications across a wide range of industries, including:

 

- Aerospace

- Food Service

- Electronics

- Telecommunications

- Jewelry Manufacturing

 

automatic tin plating machine

Basic Tin Plating Processes

 

There are three primary types of tin plating, each involving the deposition of an electrolytic tin solution onto the surface of a metal object:

 

- Barrel Plating: This method is typically used for smaller parts. The objects are placed in a specially designed barrel that slowly rotates while submerged in the electrolytic plating solution. While barrel plating is highly cost-effective, it takes a relatively long time to complete the process.

 

- Rack Plating: Ideal for larger or more delicate parts that aren't suitable for barrel plating, rack plating involves hanging the objects on a rack and immersing them in the plating solution. Though more labor-intensive and costly than barrel plating, it allows for better control over plating thickness and is more effective in reaching deep cavities.

 

- Vibratory Plating: Also used for delicate components, vibratory plating places parts in a basket with metal buttons and an electrolytic plating solution. A generator creates a vibrating action that causes the parts to move and contact the metal buttons. This method is typically the most expensive form of tin plating and requires a special drying process, which may lead to bending of the parts.

 

Tin Plating Process Elements

 

Tin can be electrodeposited onto just about any type of metal. Let’s take a closer look at the specific components of an effective tin plating process:

 

1. Cleaning

 

Before immersing the substrate—the part receiving the tin coating—into the plating bath, it’s crucial to clean it thoroughly. This process removes oil, grease, and other surface contaminants that can compromise the effectiveness of the plating.

 

Cleaning is a multi-step process that may vary based on the substrate's composition, the level of grime, and the available cleaning equipment. Generally, the cleaning process includes:

 

- Grit Blasting: This method uses pressurized air to project media such as crushed glass, aluminum oxide, silicon carbide, steel, corn cob, or walnut shells to eliminate foreign matter from the surface.

 

- Boiling: Boiling the substrate in water effectively removes grease and oil without needing chemical additives.

 

- Electrolytic Degreasing: Immersing the substrate in an electrolytic solution helps eliminate grease and oil that accumulate in cracks, crevices, and other hard-to-reach areas.

 

- Rinsing: After electrolytic degreasing, rinsing the substrate in water removes any remaining cleaning solution and surface debris.

 

2. Preparing the Plating Bath

 

The next step involves preparing the electrolytic solution, commonly referred to as the plating bath. Electrolytic tin plating baths can consist of acid tin, alkaline tin, or methyl sulfonic acid solutions. The plating bath contains dissolved tin that forms positively charged ions suspended in the solution, along with various chemical additives. This bath acts as the conductive medium during electrodeposition.

 

Acid baths are more frequently used because they achieve a higher deposition rate. While they generally provide a uniform coating, they may not consistently reach holes or other surface irregularities.

 

3. The Electrodeposition Procedure

 

After cleaning, the substrate is immersed in the electrolyte bath, preparing it for the tin coating electrodeposition. The object is positioned at the center of a specially designed tank filled with electrolytic solution, acting as the cathode—the negatively charged electrode in the circuit. Meanwhile, anodes, or positively charged electrodes, are placed near the tank's edge.

 

Next, a low-voltage DC current is introduced into the plating bath using a rectifier to convert AC power. This electrical current causes positively charged ions at the anode to flow through the electrolyte towards the negatively charged cathode (the substrate), where they are deposited onto the surface. The current then returns to the anode, completing the circuit.

 

4. Post Electroplating Process

 

Post-treatment is typically not required after the tin plating process. However, in certain applications, passivation—a light coating of protective material—may be applied to enhance corrosion protection or improve the reactive properties of the tin. Additionally, heat treatment may be utilized to prevent hydrogen embrittlement, a condition that weakens the metal due to exposure to hydrogen.

 

Common Tin Plating Issues

 

Several issues can arise during the tin plating process, negatively affecting the final product. These include:

 

Tin Whiskers: Small, sharp protrusions known as whiskers can develop on the surface of pure-tin-plated objects long after plating. Although these microscopic metal fibers are not visible to the naked eye, they can cause significant damage, particularly in electronic components where they may lead to short circuits. Tin whiskers have been linked to failures in computer systems, satellites, and disruptions in nuclear power plant operations. The exact cause of tin whisker formation is not fully understood, and there is currently no proven method to entirely prevent their occurrence. However, modifying the crystalline structure of the tin deposit has shown some success in reducing their formation, though this approach is not foolproof.

 

Lack of Uniform Thickness: In some instances, tin may not be deposited evenly across the plated object. The shape and contour of the object can make it challenging to achieve the desired thickness, typically ranging from ten to twenty microns. On metal objects with sharp corners, for example, tin may accumulate more on the outer edges while being thinner in recessed areas. This issue can often be addressed by repositioning the anodes and adjusting the density of the DC current.

 

Perishable Solderability: While tin-plated metals are renowned for their excellent solderability, this property can diminish over time. To extend the soldering lifespan, proper deposit specification, appropriate substrate preparation, and effective packaging of the plated components are essential. For instance, sealing plated products in nitrogen-filled bags can significantly enhance solderability shelf life, sometimes by as much as tenfold.

 

Tin Alloy Plating

 

One way to enhance the tin plating process is by co-depositing tin with another metal or multiple metals. Commonly applied tin alloys include:

 

- Tin-Lead: Offers corrosion resistance and excellent solderability, producing a soft, ductile finish while helping to prevent tin whiskers.

  

- Tin-Copper: Increases the overall strength of the coating, though it may also make it more brittle and lead to insufficient wetting for soldering applications, promoting tin whisker development.

 

- Lead-Tin-Copper: Often used to reduce friction on sliding engine bearings.

 

- Tin-Silver: Enhances mechanical strength and raises maximum service temperatures, but the silver content can make this alloy cost-prohibitive for many companies.

 

- Tin-Zinc: Provides a high melting point and superior fatigue strength, though it may result in poor wettability and limited corrosion protection.

 

- Tin-Bismuth: Ideal for low-temperature plating applications, this alloy offers good wettability and limits whisker formation but may not be compatible with lead-containing objects. Its low melting point makes it unsuitable for most high-temperature plating processes.

 

As an experienced tin coating machine supplier founded in 2008, Ruisite provides one-stop service for high-end electroplating/chemical plating equipment, anodizing and supporting equipment. Widely applied in military, aerospace&semiconductor integrated circuit, automotive parts, new energy industry. Automatic plating plant for sale has passed CE certification, SGS certification, ISO 9001:2015 certification.