Chap. Introduction plating
Plating Definition: electroless gold plating is a method for short. Plating is plated parts (products), immersion plated with metal ions like syrup, and connected in the cathode, the other end put the appropriate medicine anode (soluble or insoluble), through to direct current, the plating surface of the precipitation a layer of metal film method.
The basic five elements plating：
1. Cathode: The coating material, means a variety of connector terminals.
2. Anodes: If the soluble anode, was like gold-plated case. If the insoluble anode, most of precious metals (platinum, iridium oxide).
3. Electroplating solution: For gold-plated with the plating metal ion solution.
4. Electroplating tank: affordable, storage tank plating medicine, general considerations strength, corrosion, temperature and other factors.
5. Rectifier: to provide DC power equipment.
Plating Objective: In addition to requirements beautiful plating, the plating according to the needs of a variety of different purposes.
1. Copper: primer used to increase plating adhesion, and resistance to corrosion.
2. Nickel: primer used to enhance resistance to corrosion.
3. Gold: to improve the conductivity of contact resistance and enhance signal transmission.
4. Palladium Nickel: Improving the contact resistance of conductive and enhance signal transmission, wear better than gold.
5. Tin-lead: to enhance welding ability for the material quickly replaced by another.
Plating process: copper alloy substrate as the general (excluding washing Engineering)
1. Skim: skim is usually prepared using both alkaline and electrolytic degreasing.
2. Activation: dilute sulfuric acid or related use of mixed acid.
3. Nickel: nickel sulfate and nickel sulfamate.
4. Palladium Nickel: Department of ammonia are all present.
5. Gold: a gold cobalt, gold nickel, Gold and Iron, the most commonly used gold cobalt.
6. Tin-lead: alkyl acid series.
7. Drying: drying with hot air circulation.
8. Sealing treatment: a use of solvent-soluble type and two.
Composition of plating solution；
1. Water: at least the total impurities less than 5ppm.
2. Salts: To provide an ion plating.
3. Anodic dissolution aids: to promote and balance the anodic dissolution rate.
4. Conductive salt: enhancing medicine conductivity.
5. Additive: buffer, gloss, smoothness agents, softeners, wetting agents, inhibitors.
Plating conditions：
1. Current density: area under the plating unit to withstand the current, current density, the higher the film thickness is usually thicker, but the rough is too high, coating will burn dry.
2. Electroplating Location: plating position in the syrup, and the relative position of the anode, will affect the thickness distribution.
3. Stirring condition: the better mixing, plating efficiency is higher, air, water, wobble, etc. cathode agitation.
4. Current waveforms: the better the filter is usually the coating more uniform.
5. Bath temperature: 50 ~ 60 gold-plated, nickel-plated about 50 to 60, about 18 to 22 tin lead, nickel-palladium about 45 ~ 55.
6 bath PH: gold-plated about 4.0 to 4.8, about 3.8 to 4.4 nickel, nickel-palladium of about 8.0 to 8.5,
7. Bath weight: Basically the proportion of low conductivity solution is poor, poor plating efficiency.
Plating thickness: in all the electronic connector terminal of the plating thickness of the representation have a. Μ ``. Micro-inches, b. μm, micron, 1 μm is approximately equal to 40μ ``.
1.Tin-Lead Alloy Plating: tin-lead alloy plating
As welding purposes, the general thickness in the 100 ~ 150μ `` most.
2.Nickel Plating Nickel Plating
The electronic connector begin with primer (underplating), so in the 50μ `` general specifications above, lower standard for the 30μ ``, (may take into account the bending or cost)
3.Gold Plating Gold Plating
Electroplating process is expensive, so the electronics industry in the selection of the general specifications, taking into account the fact with the environment, the use of the object, the manufacturing cost, For through the general corrosion test must be strong over 50μ ``.
Coating Inspection
1. Visual inspection: Visual method, a magnifying glass (4 to 10 times)
2. Thickness testing: X-RAY fluorescence film thickness instrument.
3. Adhesion experiments: bending method, tape method or both.
4. Solder experiment: soldering method, the general area of over 95% of wetting can be uniform and smooth.
5. Steam aging test: test if discoloration or corrosion spots, and the subsequent solderability.
6. Anti-color experiment: using oven method, if discoloration or peeling.
7. Corrosion experiment: salt spray test, nitrate experiment, sulfur dioxide test, hydrogen sulfide experiments.
Chapter current density
The definition of current density:
Through the electrode per unit area in amperes, generally A/dm3 said. Current density in the plating operation is very important parameters, such as the nature of the coating, the coating distribution, the current efficiency, which have a great relationship. Current density is divided into anode and cathode current density, current density, the general calculation of the cathode current density of more.
Current density calculation:
Average current density (ASD) === amperage power plating tank (Amp) / plating area (dm2)
Terminals in the plating, the calculation of the cathode current density, it must first know the length of the bath and single terminal plating area, and then calculate the total plating area aqueduct.
Example: There is a continuous plating machine terminals, nickel slots length of 1.5 meters, like a terminal plating, the pitch of 2.54 mm terminals, each terminal plating area is 50mm2, today opened the current 50 Amp, how much does the average current density?
1. Electroplating tank terminal number == 1.5 × 1000/2.54 == 590 支
2. Electroplating bath plating area == 590 × 50 == 29500 mm2 == 2.95dm3
3. The average current density == 50/2.95 == 16.95ASD
Current density and plating area:
The same (or the same component) current, the plating area is smaller, the current density, plating the larger the area, the current density is smaller. As shown, if the open 100 amperes, A the exposed area the current density may be is a B, twice.
Anode current density and distance:
Structure of the different rules of terminal-like appearance, in the common current, the terminal site of the short distance from the anode of high current area known as the local (b), the site distance from the anode is called the local low-current region (a).
Current density and Harrington tank test:
Each plating solution has a certain operating range of current density generally results from the tank to see out of Harrington, Harrington slot because the anode surface and cathode surface is not parallel between the surface, away from the anode closer to the cathode surface The current density far away from the anode surface are large, therefore, can be part of a high current density and low current density portion of the plating conditions.
Sub-current density and plating tank:
Terminals in the dip, due to the conductive terminals at both ends in the external tank plating promoter, so cathode (terminal) electron flow is from both ends of the sub-tank to tank transfer, resulting in the sub-tank plating both ends of the terminal is exposed the current (high current region), much larger than the sub-slot at the terminal is exposed to the middle of the current (low current area).
Current density and the location of terminals in the plating bath:
Trough in the plating bath as the anode is fixed, and the height is much larger than the anode terminal height, so the cathode (terminal) in the plating bath in local areas often have to withstand high current group.
Chapter III, electroplating calculations
Productivity calculation:
Production capacity = speed / distance between terminal
Capacity (KPCS / HR) = 60L / P (L: Production speed (m / min), P: pin pitch MM)
For example: the production of a certain kind of terminal. Terminal spacing is 5. 0MM, production speed of 20 m / min, what capacity?
Capacity (KPCS / Hr) = 60 × 20 / 5 = 240KPCS/Hr
Of calculating consumption: gold plating (or palladium plating) the use of insoluble anodes (such as white Jintai Gang), so the consumption of liquid transition metal ions can not only supply their own. Add a way to add to rely on. Gold is generally gold salt (gold potassium cyanide) PGC to supplement, and palladium metals are palladium salts (such as palladium chloride. Palladium nitrate or palladium chloride) to add.
The amount of this paragraph will be added simplified formula:
Metal consumption (g) = 0.000254AZD (D: for the metal density g/cm3)
① gold consumption (g) = 0.049AZ (gold density 19.3g/cm3)
PGC consumption (g) = 0.0072AZ
② palladium consumption (g) = 0.00305AZ (Pd density 12.0g/cm3)
③ silver metal consumption (g) = 0.02667AZ (silver metal density is 10.5 g/cm3)
A: for the plating area of Z: for the plating thickness
Theoretically 1PGC gold as 0.6837g, but in fact create 1Gpgc, gold content is about 0.682g
Of the spectrum.
For example: there is a continuous terminal plating machine, want to produce a terminal 10000, gold plated full 3μ ``, each terminal plating area of 50mm2, the average thickness of the actual plating 3.5μ ``, Will need to add much gPGC?
① 10000 total area = 10000 × 50 = 500000 mm2 = 50dm2
② consumption of pure gold content = 0.0049AZ == 0.0049 × 50 × 3.5 == 0.8575g
③ consumption volume == 0.8575/0.682 == 1.26g PGC
Or the amount of consumption PGC == 0.0072AZ == 0.0072 × 50 × 3.5 == 1.26g
Cathode plating efficiency calculated as follows: General Calculation of cathode plating efficiency (referring to average efficiency) in two ways, as follows:
Cathode plating efficiency E == actual average plating thickness Z `/ Z theory plating thickness
For example: Suppose nickel plating, plating thickness theory 162μ ``, but the actual measured thickness of 150μ ``, ask the cathode plating efficiency?
E == Z `/ Z == 150/162 == 92.6%
Cathode nickel plating efficiency generally are above 90%, 90/10 tin-lead plating efficiency of the cathode about 80%, gold plating solution depends on the size of the metal ion content is very different. If you can not achieve the desired cathode plating efficiency, you can upgrade from the blender or the ability to check the composition of plating solution.
Calculation of plating time：
Plating time (min) == plating sub-slot length (m) / Production speed (m / min)
Example: a continuous plating equipment, nickel plating for each sub-slot length of 1.0 meters, a total of five, the production rate of 10 m / min, may I ask how much plating time?
Plating time (min) == 1.0 × 5 / 10 == 0.5 (points)
Calculation of theoretical thickness: two Faraday's law derived from the following formula:
Theoretical thickness of the Z (μ ``)== 2.448CTM / ND
(Z thickness, T the time, M atomic weight, N charge number, D the density, C the current density)
For example: Nickel density 8.9g/cm3, charge number 2, atomic weight 58.69, how can the theoretical thickness of nickel plating?
Z == 2.448 CTM / ND
== 2.448CT × 58.69 / 2 × 8.9
== 8.07CT
If the current density is 1Amp / dm2 (1ASD), plating time was one minute, the theoretical thickness
Z == 8.07 × 1 × 1 == 8.07μ ``
Theoretical thickness of gold == 24.98CT (density 19.3, molecular weight 196.9665, charge 1)
Theoretical thickness of copper == 8.74 CT (density of 8.9, molecular weight 63.546, charge 2)
Theoretical thickness of silver == 25.15 CT (density 10.5, molecular weight 107.868, charge 1)
Theoretical thickness of palladium == 10.85 CT (12.00-density, molecular weight 106.42, charge 2)
Theoretical thickness of the Pd-Ni 80/20 == 10.42 CT (11.38-density, molecular weight 96.874, charge 2) |
