Chemical Nickel Plating

Electroless nickel plating / chemical nickel plating / electroless nickel deposition.

Overview of One-stop Electroless Nickel Plating Processing Capabilities:

1.Materials that can be processed include copper/copper alloys, aluminum/aluminum alloys, iron/iron alloys, steel/stainless steel, zinc/zinc alloys, magnesium/magnesium alloys, titanium/titanium alloys, plastic parts, etc. In addition, materials such as tungsten steel, canna alloys, ceramics, glass, etc. can also be processed with one-stop electroless nickel plating.

2.Workpiece dimensions: 0.1mm-1500mm (workpieces within 1.5 meters can be processed).

3.Coating thickness: 1μm-20μm.

Introduction to Electroless Nickel Plating Processing Technology.

Chemical nickel plating, also known as electroless nickel plating, chemical deposition of nickel, or non-electrolytic nickel plating, is a method of depositing a layer of nickel on a metal component surface through oxidation-reduction reactions without the use of external current. The specific process involves the reduction of metal ions in an aqueous solution under certain conditions, which then precipitate onto the surface of a solid substrate. According to ASTM B374 (American Society for Testing and Materials), autocatalytic plating is defined as “deposition of a metallic coating by a controlled chemical reduction that is catalyzed by the metal or alloy being deposited.” This process differs from displacement plating in that the coating can be continuously thickened, and the plating metal itself has catalytic properties.

Chemical nickel plating is used to improve corrosion resistance and wear resistance, increase gloss and aesthetics, and is suitable for bright nickel plating of small parts with complex shapes or tubes, without the need for polishing. The component to be plated is generally immersed in a mixed solution containing nickel sulfate, sodium dihydrogen phosphate, sodium acetate, and boric acid. Under certain acidity and temperature conditions, the nickel ions in the solution are reduced to atoms by sodium dihydrogen phosphate and deposited on the surface of the component, forming a fine and bright nickel coating. Steel components can be directly plated with nickel. Tin, copper, and copper alloys must be contacted with an aluminum sheet on their surface for 1-3 minutes to accelerate chemical nickel plating.

Classification of Chemical Nickel Plating:

According to the pH value of the plating solution, it can be classified into three categories: acidic, neutral, and alkaline.

According to the deposition temperature, it can be classified into three categories: low temperature, medium temperature, and high temperature.

According to the alloy composition, it can be classified into three categories: low-phosphorus, medium-phosphorus, and high-phosphorus.

According to the reducing agent used, it can be classified into Ni-P, Ni-B, etc.

Materials Suitable for Chemical Nickel Plating:

Chemical nickel plating is almost suitable for nickel plating on all metal surfaces, such as steel nickel plating, stainless steel nickel plating, aluminum nickel plating, copper nickel plating, etc. It is also suitable for nickel plating on non-metal surfaces, such as ceramic nickel plating, glass nickel plating, diamond nickel plating, carbon sheet nickel plating, plastic nickel plating, resin nickel plating, etc. Its scope of application is very wide.

Technical characteristics and effects of Chemical Nickel Plating:

Strong corrosion resistance:

The metal surface treated by this process is a non-crystalline coating, which has excellent corrosion resistance. Compared with 1cr18Ni9Ti stainless steel, its corrosion rate is lower in sulfuric acid, hydrochloric acid, caustic soda, and saltwater comparative tests.

Good wear resistance;

Since the catalyzed surface is in a non-crystalline state, it is in a basic plane state and has self-lubricating properties. Therefore, the friction coefficient is small, the non-sticking performance is good, and the wear resistance is high. Under lubrication, it can replace hard chrome.

High glossiness:

The surface of the catalyzed plating has a glossiness of LZ or ▽8-10, which is comparable to stainless steel products and has a bright stainless steel color. After the workpiece is coated, the surface smoothness is not affected, and no further processing or polishing is required.

High surface hardness:

After processing with this technology, the surface hardness of the metal can be increased by more than twice, reaching Hv570 on steel and copper surfaces. The hardness of the coating can reach Hv1000 after heat treatment, and the service life of the tool and die coating can be increased by more than three times.

Strong adhesion:

The alloy layer processed by this technology has a stronger adhesion to the metal substrate, generally without peeling, flaking, or bubbles under the conditions of 350-400 Mpa, and the adhesion strength with aluminum can reach 102-241 Mpa.

Good conformity:

There is no excessively obvious thickening at the sharp corners or protruding edges, that is, it has good conformity, and no grinding is required after plating. The thickness and composition of the deposited layer are uniform.

High adaptability to process technology:

Uniform plating can be obtained on the inner surface of blind holes, deep holes, pipes, corners, and gaps. Therefore, no matter how complex your product structure is, this technology can handle it with ease, without any missed plating areas.

Low electrical resistance and good weldability.

H High-temperatureresistance:

The melting point of the catalytic alloy layer is 850-890 degrees Celsius.

Chemical nickel plating processing technology process.

Basic Steps:

Electroless Nickel Plating:

Tin is a silver-white metal that is non-toxic and has excellent welding and ductility properties. It is widely used in industries such as electronics, food, and automobiles. There are two main types of tin plating on brass solutions: alkaline and acidic. The acidic system is further divided into sulfate, methylsulfonic acid, and fluoroboric acid tin plating on brass systems. In actual production, the acidic bright tin plating on brass process using sulfate and methyl sulfonic acid systems is more commonly used.

The Tin plating on brass has the following characteristics and uses:

A.

Electroless nickel plating is generally divided into "displacement type" and "self-catalytic" type, and there are many formulations, but high-temperature plating produces better quality coatings regardless of the type used.

B

Nickel chloride is commonly used as the nickel salt.

C

Commonly used reducing agents include hypophosphite, formaldehyde, hydrazine, borohydride, and amine borane.

D

Citrate is the most commonly used chelating agent.

E

The acidity and alkalinity of the bath solution need to be adjusted and controlled. Traditionally, ammonia is used, but some formulations use triethanolamine, which can adjust the pH and is stable at high temperatures. It also forms a chelating agent with sodium citrate to facilitate the efficient deposition of nickel on the plated parts.

F

The use of hypophosphorous acid can not only reduce pollution problems, but also has a significant impact on the quality of the coating due to its phosphorus content.

G

This is one of the formulations for an electroless nickel plating bath.

Analysis of formula characteristics:

A.

PH effect: PH below 8 will cause turbidity, PH above 10 will cause decomposition, but has no significant effect on the phosphorus content and deposition rate.

B

Temperature effect: Temperature has a significant effect on the precipitation rate. The reaction is slow below 70°C and the rate is too fast and uncontrollable above 95°C. The optimal temperature is 90°C.

C

Sodium citrate content in the composition concentration is high, and increasing the chelating agent concentration will decrease the deposition rate, but increase the phosphorus content. The phosphorus content of the triethanolamine system can even reach around 15.5%.

D

Increasing the concentration of sodium dihydrogen phosphate as a reducing agent increases the deposition rate, but if the concentration exceeds 0.37M, the solution will decompose. Therefore, the concentration should not be too high, which can be harmful. There is no clear relationship between the phosphorus content and the reducing agent, so the concentration is generally controlled at around 0.1M.

E

The concentration of triethanolamine affects the phosphorus content and deposition rate of the coating. Increasing its concentration will decrease the phosphorus content and slow down deposition, so it is best to keep the concentration at around 0.15M. It can be used not only to adjust the acidity and alkalinity but also as a metal chelating agent.

F

It is found that adjusting the concentration of sodium citrate can effectively change the phosphorus content of the coating.

G

Generally, reducing agents are divided into two categories: sodium hypophosphite (NaH2PO2H2O) series and sodium borohydride (NaBH4) series. Sodium borohydride is expensive, so sodium hypophosphite is mainly used in the market. The commonly accepted reaction is as follows:

The surface of copper is usually non-activated, so it needs to be negatively charged to achieve "start plating". The copper surface is first treated with a non-electrolytic palladium plating method, and there is co-deposition of phosphorus in the reaction, so a phosphorus content of 4-12% is common. Therefore, when there is a large amount of nickel, the coating loses its elasticity and magnetism, and becomes brittle and glossy, which is beneficial for rust prevention but not for wire drawing and welding.

Non-electrolytic gold plating:

A.

Non-electrolytic gold plating is divided into "replacement gold plating" and "non-electrolytic gold plating". The former is also called "immersion gold plating", where the plating layer is thin and stops when the bottom surface is fully plated. The latter accepts a reducing agent to supply electrons, allowing the plating layer to continue to thicken without the use of an electric current.

B

The reduction reaction can be expressed as follows: reduction half-reaction: Au + e- → Au0, oxidation half-reaction: Reda + Ox + e- → Red a Ox.

C

In addition to providing gold source complexing agents and facilitating the reduction reaction with reducing agents, chemical gold plating formulas must also use chelating agents, stabilizers, buffering agents, and swelling agents to achieve their full potential.

D

Some research reports have shown improvements in efficiency and quality of chemical gold plating, and the choice of reducing agent is crucial. From early use of formaldehyde to more recent borohydride compounds, potassium borohydride has the most common and effective results, and better results can be achieved by using it with other reducing agents. The representative reaction formulas are as follows: reduction half-reaction:

E

The deposition rate of the plating layer increases with increasing concentrations of potassium hydroxide and reducing agents, and with increasing bath temperature, but decreases with increasing potassium cyanide concentration.

F

The operating temperature of the commercialized process is mostly around 90°C, which is a big challenge for material stability.

G

If lateral growth occurs on fine line substrates, there is a risk of short circuits.

H

Thin gold layers are prone to porosity, which can lead to galvanic cell corrosion. The problem of porosity in thin gold layers can be solved by post-treatment passivation with phosphorus-containing methods.

Key Process Points

Alkaline Degreasing

To prevent lateral diffusion during palladium deposition, a citric acid-based cleaner was used initially. Later, due to the hydrophobic nature of the green paint and the better performance of alkaline cleaners, a non-ionic cleaner based on phosphate was adopted, with easy cleaning as the goal and to prevent acidic cleaners from causing copper passivation.

Microetching

The goal is to remove oxides and obtain a fresh copper surface while achieving an absolute roughness of about 0.5-1.0μm on the copper surface, so that a corresponding roughness can still be obtained after nickel plating, which is helpful for the tensile strength during wire bonding. The plating solution consists of SPS 150g/l with a small amount of hydrochloric acid to maintain a chloride ion concentration of about 200ppm and improve etching efficiency.

Copper surface activation treatment

Palladium is about 3ppm, operated at about 40°C for one minute. Since chloropalladite is faster than sulfide palladium in passivating copper surfaces, sulfide palladium is more appropriate for better nickel adhesion. Since there will be a small amount of Cu generated due to the action of palladium, which may be reduced to Cu or oxidized to Cu, if it becomes a copper atom, it will affect the reduction of palladium. To ensure smooth palladium reduction, air agitation is required with a flow rate of above 0 to promote the oxidation of cuprous ions and release of electrons to reduce palladium and complete the electrodeless nickel deposition.

Activated Water Rinse

To prevent the diffusion of nickel, it is essential to remove residual palladium between the lines. In addition to strong water rinsing, some people use dilute hydrochloric acid immersion to convert dead-end sulfided palladium to prevent nickel diffusion. To promote nickel reduction, a hot water pre-soak will help with growth and uniformity. The idea is to increase activity to make the difference between size, area, and high and low voltage smaller and achieve uniformity.

Electroless Nickel

The operating temperature is 85±5°C, pH 4.54.8, and the nickel concentration is about 4.95.1 g/l. The nickel concentration in the bath should be kept below 5.5 to prevent the precipitation of hydroxides. If it is lower than 4.5 g/l, the plating speed will slow down. Normal precipitation should be at 15μm/hr, and the bath loading should be kept at about 0.51.5)dM2/l. The standard nickel content in the plating solution is 5 g/l, and the tank must be replenished after 5 turns; otherwise, the quality of the deposited nickel will deteriorate. The nickel tank can be made of 316 stainless steel, and the tank should be passivated with 50% nitric acid beforehand. The cathode can be connected to the stirring blade with a low current of 0.20.4 A/M2 (0.0180.037 ASF), but care must be taken not to produce bubbles in the blade area, which indicates that the current is too strong or the nickel plating layer is too thick and the tank must be burned. The pH of the plating solution should be maintained between 54.7, which can be adjusted with NaOH or H2S04. If the pH is lower than 4.8, turbidity may occur, and the pH operating range of the bath solution will gradually increase as it ages to maintain normal precipitation speed. Because the bottom of the line is a dead-end, it is easy to leave residual alkali after the reaction, which may have an adverse effect on the green paint. Therefore, it is necessary to strengthen the stirring and vibration to remove residual alkali and bubbles.

Electroless Nickel Phosphorus Content

Generally, electroless nickel uses “sodium hypophosphite” as a reducing agent, so the coating will contain a certain amount of phosphorus, about 46%, some of which are in a crystalline form. If the phosphorus content is in the range of 68%, most of the content is in a non-crystalline form. When it is above 12%, almost all of it is in a non-crystalline structure. As far as wire bonding is concerned, the medium phosphorus content and hardness are best at 500~600HV, and the solderability is also best at 9%. Generally, after adding four times, the precipitation phosphorus content will reach 10%, and the tank should be considered for replacement. The wire bonding thickness should be above 130μ.

Non-electric gold plating

Using citric acid as a complexing agent, a chemical gold bath is prepared with a gold concentration of 5g/L, and the bath body is made of PP material. At a pH of 5.1-5.3, it can react with copper, and at a pH of 4.5-4.8, it can react with nickel to carry out gold plating, which can be adjusted by citric acid. The general operating temperature is around 85°C, and the thickness will stop at about 2.5μm. This thickness can be achieved in about five minutes. Although a higher temperature can accelerate the process, the corrosion resistance may be worse due to the coarsening of crystals. Since most of the reactions are replacement reactions, a significant amount of nickel will dissolve into the solution. Therefore, it is best to keep the nickel concentration below 200ppm. When the concentration reaches 40ppm, the appearance and adhesion of the metal will deteriorate, and the solution may even turn green or black, which requires a new bath. The gold bath is highly sensitive to copper ions, and the precipitation of copper ions above 20ppm will slow down the process and increase stress. The plated nickel should not be left for too long to avoid passivation, which can prevent the deposition of gold. Therefore, after rinsing, it should be promptly placed in the gold bath. Sometimes, soaking in 10% citric acid can improve the adhesion in specific situations.

After gold plating, the plated surface may still have some porous spots. Therefore, the plated parts should be treated with a sealing process after rinsing with water. This can increase the corrosion resistance of the bottom nickel layer by treating it with organic phosphorus.

Chemical Nickel Plating

Chemical Nickel Plating

Overview of One-stop Electroless Nickel Plating Processing Capabilities:

Introduction to Electroless Nickel Plating Processing Technology.

Classification of Chemical Nickel Plating:

Materials Suitable for Chemical Nickel Plating:

Technical characteristics and effects of Chemical Nickel Plating:

Strong corrosion resistance:

Good wear resistance;

High glossiness:

High surface hardness:

Strong adhesion:

Good conformity:

High adaptability to process technology:

H High-temperatureresistance:

Chemical nickel plating processing technology process.

Basic Steps:

Electroless Nickel Plating:

A.

B

C

D

E

F

G

Analysis of formula characteristics:

A.

B

C

D

E

F

G

Non-electrolytic gold plating:

A.

B

C

D

E

F

G

H

Key Process Points

Alkaline Degreasing

Microetching

Copper surface activation treatment

Activated Water Rinse

Electroless Nickel

Electroless Nickel Phosphorus Content

Non-electric gold plating

Chemical nickel plating processing sample case.

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