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Electroless Nickel-Phosphorus-M value/procedure

Properties of Electroless Nickel

The properties of electroless nickel including corrosion resistance are influenced by the type of alloy. This can be a low phosphorous nickel coating, a medium phosphorous nickel coating, a high nickel phosphorous coating or a nickel boron coating.

The table below outlines the various properties and nickel alloy type.

Property / Level of alloy High a Mid a Mid-Low a Low a Mid-Low Bb Low Bb
% Phosphorous 10 – 13 7 – 9 4 – 6 1 – 3
% Boron 3 – 5 0.2 – 1
Deposit density Range (g/cm3) 7.6 – 7.9 8.0 – 8.2 8.3 – 8.5 8.6 – 8.8 8.25 8.8
Plating rate (µ/Hr) 7.5 – 15 7.5 – 15 18 – 30 11 – 19
Hardnessc,f 400 – 525 500 – 600 625 – 750 725 – 800 650 – 750 600 – 700
Rockwell C (Rc) Hardness 41 – 46 45 – 51 53 – 59 57 – 61 54 – 59 51 – 56
Hardness after heat treatc 850-950 850-1000 850-1100 900-1100 1100-1200 500-600
Taber wear indexe,f 22 – 24 16 – 20 10 – 14 7 – 12 3 – 10 7 – 9
Coefficient of thermal expansiong 8 – 10 10 – 15 11 – 14 12 – 15
Electrical resistivityh 75 – 110 40 – 70 15 – 45 10 – 30 40 – 90 10 – 20
Thermal conductivityi 0.010 0.012 0.016 0.015
Tensile strength (MPa) 650-900 800-1000 350-600 200-400
Elongation 1 – 1.25 0.5 – 1 0.5 -1 0.5 – 1.5 0.2
Modulus of elasticity (GPa) 55 – 70 50 – 65 45 – 65 55 – 65 120
Melting rangeoC 880-900 880-980 1100-1300 1250-1360 1040-1080 1350-1390
Coercivity (Oe) 0 1 – 8 10 -15 15 – 80
Magnetic propertiesf Non Slightly Magnetic Magnetic Weakly
Internal stressf Neutral to comp Slightly tensile Slightly comp Slightly tensile Tensile
Step by Step procedure for Electroless Nickel Plating PN: (For Deposit Stress Analyzer System)

Step 1: To remove finger oils, dip the test strip in a soak cleaner solution, water rinse.

Step 2: If a nickel strike is necessary, place the test strip in a Wood’s nickel strike bath.

Step 3: With the test strip negatively charged, plate the test strip for 30 seconds at 0.42 amps.

Step 4: Rinse the test strip in water and rinse in isopropyl alcohol and dry.

Step 5: Weigh a PN: 270NI test strip to the nearest thousandth of a gram and record the weight so the weight of the deposit can be determined later after plating. This value is necessary to calculate the deposit thickness prior to calculating the deposit stress.

Step 6: Place it in the electroless nickel alloy plating bath. Plate the test strip until the test strip leg tips separate at a distance of no more than 20 total units spread on the Deposit Stress Analyzer.

Step 7: Then remove the test strip, rinse it in water and isopropyl alcohol, blot it between a folded paper towel and gently pull it from between the layered paper towel to dry it. This will not alter the test strip leg tip spread distance since its tension memory remains unaffected.

Step 8: Place the plated test strip in the PN: 683 Deposit Stress Analyzer and read and record the total number of increments spread between the test strip leg tips. If the test strip leg tips are not close to an even distance from the zero mark on the scale, bend the test strip with a thumb at the top where suspended from the measuring stand gently to cause the leg tips to hang at a more equal distance from the zero mark.

For example, 2.4 on the left side of zero + 3.1 on the right side of zero = 5.5 which becomes the value for U in the formula S = UKM / 3T.

NOTE: The plating test should be continued until the test strip legs deflect from up to 20 units spread for the most accurate results. The required plating time can be determined experimentally by examining the degree of spread after each minute of plating. Metallic deposits should not exceed and average thickness of 100 microinches. If the stress is near zero, a reading as low as 1 unit may result.

Step 9: Weigh the test strip and obtain the deposit weight by subtraction.

Step 10: Solve the formula T = Grams of Deposit divided by the multiplication of the Deposit Specific Gravity x 7.74 square centimeters x 2.54 centimeters per inch.

The value of T will be in inches.

K is the calibration value determined by Specialty Testing and Development Company and is marked on each package.

M = the plating deposit modulus of elasticity as PSI (pounds per square inch), divided by 30,000,500 PSI (the nickel test strip material modulus of elasticity).

The deposit value for the electroless nickel alloy coating can be obtained from the Table- select the mid range that pertains to the alloy that is being deposited. Note the values on the Table are in GPa.

Step 11: Solve the DSA formula to determine the deposit stress as PSI per above chart.


Deposit Thickness Formula For Chemically Applied Deposits:

T  =    ──────────────────   =   cm      where
            D (87.53cm²) (2.54cm²/in²)

W = Deposit weight in grams,

D = Deposit specific gravity in grams/cm³= 8.88g/cm³ for pure nickel deposits.

Electroless Nickel

The values for E and M are required to accurately solve the Stoney Formula and the value M is required to solve the Deposit Stress Analyzer Formula.

M = EDeposit ÷ ESubstrate

Frequently, the increase that the Modulus of Elasticity effects on the internal deposit stress of electroless applied alloy coatings is not recognized. Numerous formulas for calculating the internal deposit stress of metallic deposits do not include a correction for the difference of the Modulus of Elasticity between the deposit and the substrate material. In such cases, the calculated result can be far from the actual value. Call the supplier of your electroless nickel alloy plating chemistry for the Modulus of Elasticity value of the deposit.

Note: how necessary it is to use the value for M to determine the actual internal deposit stress value in calculating results for the bent strip method or for the spiral contractometer method. Often the results are calculated without incorporating the correct value of E in these formulas by assuming that electroless nickel deposits have a Modulus of Elasticity similar to that of pure nickel deposits, or they fail to include the value for M in the equations altogether.