Ginplate Electroless Nickel Coatings
GENERAL REACTION SCHEME
Ginplate Electroless Nickel are chemicals plating processes that auto-catalytically deposit nickel alloys with up to 12% by weight phosphorous or up to 5% by weight boron. Electroless Nickel deposits are produced by chemical reduction of nickel onto catalytic metallic or catalyzed non-metallic substrates. Since the process requires no electrical current (as used in electrolytic deposition of chromium or nickel), the result is a very uniform coating that has a dense, essentially amorphous structure as plated.
Blind holes, threads, channels, recesses or internal areas receive the same amount of plate as sharp corners, edges or flat surfaces. Therefore, total as plated thickness can often be reduced and close tolerances (within 1.2 to 2.5 µm) maintained. Although Electroless Nickel deposits can be machined; machining to size is frequently eliminated. Deposition of nickel phosphorous or nickel boron coatings occur by the following chemical reactions.
Hypophosphite reduced process
H2PO2 -+ Ni++ + H2O +Nio + Po + H2PO3 -+ 2H+
Amine Borane reduced process
[CH3]2NHBH3 + 3Ni ++ + 3H2O +3NiO + B + H3BO3 + 2H2 + H+ + [CH3]2H2N+
FEATURES OF GINPLATE ELECTROLESS NICKEL
Ginplate Electroless Nickel coatings offer excellent deposit uniformity coupled with a wide variety of important features. These features can vary considerably from one Ginplate Electroless Nickel process to another. Specific product recommendations are available from our Growel representative.
Features of Ginplate Electroless Nickel Coatings
SUBSTRATES THAT CAN BE PLATED WITH GINPLATE ELECTROLESS NICKEL
- Corrosion resistant
- High hardness
- Abrasion resistant
- Low friction and wear characteristics
- Quick release properties
- Non-magnetic or magnetic deposits
- Solderability, bondability
- Diffusion barrier
- Compressive stress, good fatigue properties
Ginplate Electroless Nickel can be plated onto a variety of substrates with excellent adhesion, if proper surface preparation procedures are followed.
Grauer & Weil has developed a number of Ginplate Electroless Nickel processes designed to meet specific performance needs. Among them are processes to meet the demands of high volume production plating operations where low cost, high speed and consistency in process reliability is necessary. Processes are also available to satisfy deposit requirements needed in engineering and electronic applications. Tables 1, 2, 3, 4 and 5 provide specific product information on different Ginplate Electroless Nickel processes.
SUBSTRATES PLATEABLE WITH GINPLATE ELECTROLESS NICKEL
- Beryllium Copper, Leaded Brass
- Carbon Steels
- Stainless and High Alloy Steels
- Cast Iron
- High Nickel Alloys
- Aluminum and its alloys
- Aluminum Die or Sand Castings
- Other Non-conductors
- Zinc Die castings
- White or Slush Metal (Tin alloys)
- Brass, bronze
GINPLATE ELECTROLESS NICKEL PRODUCT LINE
- Low phosphorous, alkaline electroless nickel bath that provides very thin deposit at low temperature
- Aids in plating aluminum, promotes adhesion
- It is excellent for electronics applications including ceramics
- Has good solderability and conductivity.
- Highly stable electroless nickel bath that rapidly deposits uniform, conductive coating in plastics and other non-conductors
- It is designed primarily for use in no-rerack cycles
- Bulk electroless nickel plating may also be followed by plating in bright acid copper as a basis for further plating operations.
- Stable, high-speed, bright production bath
- Economical to operate
- Optional pH adjustment with NH4OH or liquid K2CO3.
- Stable, semi-bright, functional electroless nickel process
- Superior deposit properties including excellent corrosion resistance
- Nonmagnetic properties
- Good elongation and low stress.
- Stable functional process for high wear and abrasion applications in high temperature exposure
- Suited for electronics applications where solderability, conductivity, etc, are needed
- Multi-temperature operation at near neutral pH.
- Highly stable, high-speed, high hardness and wear resistant
- It has excellent brightness and a low operating cost.
- Excellent corrosion resistance, suitable for high build-up applications
- Good lubricity, wear & abrasion resistance
- Narrow melting temperature
- Suitable for brazing & welding
- Good stability.
- Lead, Cadmium free
- Meets ROHS & ELV directives
- Mid phosphorous (~ 6 - 8%)
- Brighter in apperance
- Stable & easy to control.
- Uyemuras unique electroless Nickel - PTFE composition coating
- Good mold releasing and wear resistance properties
- Excellent in lubricity & uniform pore free coating.
PROCESS SELECTION GUIDE
- Uyemuras unique electroless Nickel - boron Coating
- Excellent solderability, deposit hardness, wear resistances & conductivity.
PERFORMANCE PROPERTIES OF GINPLATE ELECTROLESS NICKEL COATINGSDEPOSIT STRUCTURE
Ginplate Electroless Nickel-Phosphorous deposits have a dense structure, which is essentially amorphous as plated. This structure varies with phosphorous content, deposition rate and process control methods. Deposits with greater than a 10% phosphorous content tend to have a particularly dense, amorphous structure. Figures 1 and 2 show the deposit structure of a 10 to 12 weight percent phosphorous content deposit (Ginlate Ni-422) plated on a smooth polished aluminum surface and on a rough sand blasted surface.
Nimuflon ~ electroless Nickel-PTFE (Polytetrafluoroethylene) composite coating is non-magnetic & amorphous in nature. Embeded PTFE influence the lubrication properties by reducing coefficient of friction of the deposit. The SEM images of the deposits using Nimuflon process at different PTFE content are shown in fig.1a.
BEL 801 ~ Electroless Nickel - Boron deposits have a dense structure which is essentially amorphous as plated. The structure varies with boron content, deposition rate and process control methods. The deposits produced with low boron content and slow plating rates have reduced porosity. All Electroless Nickel-Boron deposits tend to have high plated hardness vales, particularly for the deposits with boron content greater than 3%.
An important feature of Ginplate Electroless Nickel deposits, compared to alternative electrolytic deposits such as hard chrome or electrolytic nickel, is its excellent uniformity. The chemical nature of the electroless plating process avoids areas of high and low current density which are typical of electrolytic plating. Thus, as shown in Figures 3, 4 and 5, problems associated with heavy deposit build-ups at corners along with minimal or no coverage in recesses can be eliminated using Ginplate Electroless Nickel.
This excellent deposit uniformity allows complex shaped parts, recessed areas, channels, threaded components, etc. to be coated evenly and accurately to within required tolerances (see Figure 6). Deposits can be plated to within 50 to 100 millionths tolerance consistently on most production parts. Closer tolerances are also achieved commercially, but require very close process controls during plating. Large parts, such as cylinders can be plated directly to thickness with electroless nickel avoiding costly post grinding or honing operations (see Figure 7). In certain instances an initial deposit layer of electroless nickel is used to help eliminate 'under-plate' or 'no plate' in low current areas on complex parts that specify an electrolytic deposit such as hard chromium, for the final finish.
PHYSICAL AND MECHANICAL PROPOERTIES OF ELECTROLESS NICKEL DEPOSITS
Electroless Nickel deposits have a number of important physical and mechanical properties. Typical results for 'as plated' nickel-phosphorous deposits are noted below in Table 3.
PERFORMANCE PROPERTIES OF NICKEL COATINGS
When optimum corrosion protection, low stress, good elongation and/or reduced pitting at high thicknesses are desired, the recommended electroless nickel processes normally do not have a high level of decoration brightness.
Following the recommended pre-treatment procedure, Ginplate Electroless Nickel coatings can achieve bond strengths of 2800 to 4200 Kg/cm2 on steel and 1050 to 2450 Kg/cm2 on aluminum. (Determined by the Ring Shear Method).
The 1800 Mandril Bend Test (ASTM B-571) is easily passed with Ginlate Electroless Nickel coatings. Heavier deposits of Electroless Nickel (>25 µm) may show parallel line cracks and/or eventual panel fracture due to the added stresses imparted to the base metal. Proper adhesion of the coating, however, should still be evidenced by no flaking or exfoliation of the plated deposit. Ginplate Electroless Nickel coatings can also pass other adhesion tests such as Thermal Shock or Impact Test (ASTM B-571-84).
HYDROGEN EMBRTITTLEMENT / STRESS RELIEF
Hydrogen embrittlement, attributable to the Electroless Nickel plating process, has not been found to be significant. Generally, if the tensile strength of the base metal is above 1050 MPa, heat treatment of the Electroless Nickel deposit at 190 to 230oC for two hours or more (depending on the tensile strength of the steel) within a specified time period after plating is recommended to achieve stress relief (ref ASTM B-656). Embrittlement relief is required after plating on high strength steels and other high tensile strength base materials.
Stress relief of base metals before plating is also necessary if the substrate has a tensile strength above 1050 MPa. Stress relief should be performed at similar temperatures to those specified for hydrogen embrittlement relief.
Most Ginplate Electroless Nickel-Phosphorous coatings have similar 'as-plated' hardness values of 500 to 550 vickers (HV100) while BEL 801 Electroless Nickel-Boron coatings have values of 700 to 750 HV100 hardness value which can be increased by heat treating and are affected by variations in time and temperature during heat treatment. Typically, a minimum temperature of 230oC is needed to initiate precipitation hardening of nickel phosphides (Ni3P) in the nickel-phosphorous deposit. A minimum temperature of 180oC is needed to initiate precipitation hardening of nickel borides (Ni3B) in the nickel-boron deposit.
The hardness of Ginplate Nickel-Phosphorous deposits can be increased to 900 to 950 HV100100 when heat treated at a temperature of 400oC for one hour. For BEL 801 Nickel-Boron deposits heat treating at 350oC 350oC for one hour will increase the hardness to 1100 HV100 or greater. Above these temperatures, the deposits become softer due to re-crystallization. When corrosion resistance along with additional hardness is required from nickel-phosphorous deposits, a lower heat treatment temperature (300oC) is suggested. This can prevent significant micro-cracking of the coating and limit the increase in deposit porosity which can occur.
The overall relationship of hardness to heat treatment conditions is shown in Figure 8. Growel has developed high hardness Electroless Nickel deposits for special applications (see Table 3). Ginplate Ni-426 is 1 to 3% phosphorous deposits with an 'as-plated' Vickers hardness of 700 HV100. Heat treatment of the deposits increases the hardness to 950 - 1000 HV100.
Special Electroless Nickel-Phosphorous or nickel boron deposits provide superior abrasion resistance approaching the values normally obtained from hard chromium.
WEAR AND GALLING RESISTANCE
The excellent wear characteristics of Ginplate Electroless Nickel coatings make them suited for a wide range of applications and problem solving tasks. This is due to their high hardness, good adhesion, excellent lubricity, low co-efficient of friction, and uniform coverage capability. The overall wear properties of Ginplate Electroless Nickel deposits, under lubricated conditions, can be equal or even superior to hard chromium plating.
Wear tests have been conducted on Ginplate Electroless Nickel coatings in several different tests including the Falex and crossed cylinder wear tests. Results for Ginplate Ni-418 deposits in the crossed cylinder wear test are shown in Figures 9 & 10. These tests were performed with 10W lubricant and a shaft (unplated) which had a rotational speed of 100 RPM. A plated sleeve (1/2 ring) was used on the shaft which had a variable load applied to it.
Figure 9 represents crossed cylinder wear results for both hard chromium and Ginplate Ni-418 over a 664 hrs period at low load (90.7kgf). The hard chromium deposit shows low wear, but significant wear was produced on the counter face. This is attributed in part to the lack of coating uniformity. The heat treated Ginplate Ni-418 deposit shows much better overall performance for the 'wear pair' i.e. the unplated shaft and the plated sleeve. When the Electroless Nickel is sand blasted, the wear is severe on the counterface. This emphasizes the important benefit of deposit uniformity in achieving low overall wear.
Figure 10 gives wear results for Ginplate Ni-418 when the test is conducted under low load condition for a test period of 140 to 150 hrs. Lower thickness of Electroless Nickel, 7 to 18 µm tend to give better results overall due to better base metal support for the coating. The extremely high wear of Ginplate Ni-418 at 75 µ thickness is theorized as being related to a work-hardening of the surface layer which then begins to gall the softer under layer of Electroless Nickel.
Wear performance of a particular 'wear pair' is also optimized for Electroless Nickel deposits when the hardness of the Electroless Nickel deposit is adjusted (by heat treatment) to be greater than that of the mating, unplated part. Electroless Nickel coatings also tend to give slightly lower total wear if they are applied to the stationary member of the 'wear pair' rather than the rotating member. However, both situations have achieved success; commercially. When Ginplate Electroless Nickel coatings are mated against themselves under lubricated conditions, they also tend to provide good wear values and galling resistance. Under higher loads, more attention should be paid to maintaining a lower deposit thickness. Threaded components, which have acceptable tolerances remaining after plating, can be mated and re-mated easily, when both parts are coated with Electroless Nickel. Commonly up to 37 µm of Electroless Nickel can be applied without creating galling problems. Electroless Nickel coatings can provide excellent wear and anti-galling properties, when mated against stainless steel or hard chromium in a lubricated environment. In fact, these coatings are common solutions to the wear and galling problems associated with stainless steel or hard chromium. In contrast, Electroless Nickel coatings mated against soft electrolytic nickel or brass; tends to gall. CORROSION RESISTANCE
Ginplate Electroless Nickel coatings provide a range of corrosion protection from good to excellent, depending on the process selected (See Table 4 & 5). Figure 11 shows results from a 1000 hr salt spray test on two Ginplate Electroless Nickel deposits. The superior performance of Ginplate Ni-422 coating is evident at both 12.5 and 37.5 µm thickness. For relatively smooth surfaces (such as panels) deposit thickness between 12.5 and 25 µm are necessary to optimize the performance of Electroless Nickel in the salt spray test. Figure 12 shows the effect of heat treatment at 400oC for 1 hr on the salt spray performance of Ginplate Electroless Nickel.
Figure 13: WEIGHT LOSS CORROSION TEST OF COATED AISI 4130 STEEL COMPARED TO VARIOUS UNCOATED MATERIALS
The data shown in Figure 13 indicates the significant improvement in component life for AISI 4130 steel coated with Ginplate Ni-422 compared to uncoated steel in 65oC sea water. Figure 13 also shows the cost effectiveness of a 75 µm coating of Ginplate Ni-422 versus more expensive high alloy materials.
Ginplate coatings have also been evaluated in various petroleum environments and compared to uncoated carbon steel and highly
alloyed materials. Figure 14 shows the excellent corrosion resistance of a 75 µm deposit of Ginplate Ni-422 when exposed to 0.7 kg/ cm2 H2S, 14 kg/cm2 CO2 and 9% chloride. The cost effectiveness of this coating compared to the highly alloyed materials is also evident.
In general, Ginplate Ni-422 and Ginplate Ni-425 with their high phosphorous content are preferred for applications where minimal or no porosity is critical. Deposit thickness should be a minimum of 20 to 25 µm m on smooth surfaces (<50 RMS) and, typically 50 to 75 µm on rougher surfaces (>100 RMS) in order to achieve optimum results. Improper cleaning and roughness of the metal surface will increase coating porosity as well as produce poor adhesion. Heat treatment of Ginplate Electroless Nickel deposits above 300oC will tend to create micro-cracking; significantly increasing coating porosity.
Grauer & Weil has developed a number of suggested pretreatment cycles for cleaning and activating a variety of substrates. (Pretreatment brochures for steel, copper alloys and aluminum are available at Grauer & Weil on request). Special cycle modifications have also been identified for specific alloy variations. Recommended pretreatment procedures for aluminum, steel, copper alloys, other metallics and non-metallics are available from Grauer & Weil on request.
POST TREATMENT- HEAT TREATMENT
Heat treatment of Electroless Nickel deposits should be performed in an inert gas atmosphere (i.e. Nitrogen or Argon) to avoid severe discoloration due to oxide formation on the surface. Baking of the deposit to enhance adhesion on steel can be performed at temperatures of 250oC to 400oC. Lower temperatures of 250oC to 300oC can be selected to avoid metallurgical changes in the deposit. Aluminum plated parts should be baked at temperatures of 150oC to 200oC to avoid metal deformation (developed on the alloy).
Electroless Nickel deposits are covered by military specification MIL-C-26074 entitled "Coatings, Electroless Nickel, Requirements for" and by AMS specifications AMS 2404 A and AMS 2405. These specifications list the requirements for the final coating and not the requirements of the solution or the process used to obtain the coating.
When used in accordance with the recommended operating instructions and preceded by proper cleaning, de-scaling, etc. Ginplate Electroless Nickel solutions will produce an Electroless Nickel deposit which can meet the requirements of MIL-C-26074 and AMS 2404 A and AMS 2405 specifications.
PROPERTIES FOR THE ELECTRONIC INDUSTRY
ELECTRICAL AND MAGNETIC PROPERTIES
Ginplate Electronics Nickel coatings vary in both electrical and magnetic properties based primarily on the phosphorous content of the deposit. Ginplate Ni-422 and Ginplate Ni-425 are non-magnetic coatings with a phosphorous content above 10%. These non-magnetic characteristics are retained at elevated temperatures up to 275oC. Other Ginplate Electroless Nickel processes with lower phosphorous contents may be slightly magnetic as plated and will increase in magnetic properties with heat treatment. The resistivity of Ginplate Ni-422 and Ginplate Ni-425 Electroless Nickel are 75 to100 microohm/cm, due to their high phosphorous content. Resistivity values for other Ginplate Electroless Nickel deposits are lower; 20 to 25 microohm/cm, due to their reduced phosphorous contents. These values can be lowered further by heat treatment of the deposit above 250oC. Ginplate Ni-426 have very low resistivity values of 15 to 20 microohm/cm as plated.
Soldering to Ginplate Electroless Nickel is best done immediately after plating. Direct soldering to aged deposits becomes more difficult due to oxide formation on the deposit surface. When soldering must be done to aged deposits, highly active acid solder fluxes are suggested to aid in obtaining adequate wetting of the solder to the coating. Special cleaning and activation techniques may also be necessary to achieve successful soldering of aged deposits. In cases where mildly active or non-activated fluxes are dictated, the time between plating and soldering of the deposit should be kept to a minimum (<48 hrs).
BARRIER TO DIFFUSION
Ginplate Electroless Nickel deposits of approximately 100 µm are effective in preventing migration of copper or nickel into gold surface finishes.
WIRE BONDING, WELDING
Ultrasonic wire bonding and resistance welding techniques have been successfully performed on Ginplate Electroless Nickel deposits.
COMMON RANGES OF DEPOSIT THICKNESS FOR ELECTROLESS NICKEL ( µm )
Ginplate Electroless Nickel coatings are used in a wide range of industry applications. Table 6 summarizes the range of deposit thickness suggested for different types of intended service. Table 7 provides a list of common applications for Ginplate Electroless Nickel. Specific recommendations can be provided by Grauer & Weil representative.
Ginplate Electroless Nickel coatings are cost-effective compared to alternative coatings when a part has a complex configuration and good deposit uniformity is required. Deposit thickness can be controlled in commercial production within 1.2 to 2.5 µm thickness. Ginplate Electroless Nickel coatings also very cost effective when thickness up to 75 to 125 µm are specified on parts that need good deposit uniformity. Above this thickness Ginplate Electroless Nickel coatings are most cost effective in applications where part configuration and specifications demand excellent uniformity (or certain properties not achievable with other coatings).
Selective plating with Ginplate Electroless Nickel can be achieved through masking of those areas where deposition is not required. Maskants are available that can be sprayed, dipped or brushed onto parts. Special tapes are also available that can be used for masking. Consult Grauer & Weil for special recommendations.
In addition to the above specialized electroless Nickel processes are designed to meet the specific requirements. Nimuflon process is preferred to obtain the technical requirements for good lubrication due to its low co-efficient of friction. e.g. sliding components, camera parts etc.
BEL 801 is preferred to obtain higher hardness and also on electrical accessories due to its higher deposit hardness & reduced electrical resistivity.