The following states what an operator who runs the electrolytic Plating process must be able to demonstrate to the trainer and be able to answers questions on, as this is about training, the answers are below in blue.
Does the Operator Understand what P.P.E. (Personnel Protective Equipment) they should be wearing at all times when operating this line
The operator should be wearing safety glasses, lab coat and safety shoes
Does the Operator know where the Emergency Spill kit is Located
The emergency spill kit is located in the big yellow drum at goods inward
Does the Operator know where the list of First Aiders is located, and who they are
The list of first aiders are displayed at the notice bard at the entrance to the department
Does the Operator know where the Safety Datasheets are
The safety datasheets are located in the current procedures on a central point in the server, hyperlinked on all pcs and a paper copy is held in lab
Does the Operator understand the importance of the Manufacturing Route Card and that they cannot start a job before obtaining, reading and ticking additional comments if necessary.
The operator must understand that they cannot ever start a job without a jobcard, the operation column of the jobcard must be signed, the columns must be ticked, anbnd the job must be started in the shopfloor module
Can the operator demonstrate to the assessor how to jig up panels, and can the operator explain the theory of the jigging process, and the connections required
The operator must be able to show that they can jig up panels, ensuring a good connection is obtained, and that they do not jig over dry film codes etc…, and the operator must show that the current from the plating rectifier passes through the cables to the cathode rail, the current is then used to plate the coper onto the pads/holes, and varies with each job.
Can the operator demonstrate that they can use the ShopFloor Data collection terminal to start and end the job, and input any defects as required.
The operator must be able to show that they can start/end a job in the shopfloor module, and also able to explain how to record defects, and the importance of recording defects, also what is to be done with defective panels. Defects should also be recorded in the defects table on the back page of the route card.
Can the operator demonstrate to the assessor the timings of each process step and how they use the timers to ensure the panels get the correct time, and what temperatures are expected for each process step
Acid Clean – 4 mins – +/- 1min
Water Rinse – 2 mins +/- 30 secs
Microetch – 10 seconds – +/- 2 secs – wait with hand on jig
Water Rinse – 2 mins – +/- 30 secs
Sulphuric Acid Predip – Max 10 mins
Electrolytic Copper – as required typically 60 mins
Water rinse – 2 mins +/-30 secs
Tin Plate – 5 mins +/- 1 min
Water rinse – 2 mins +/- 30 secs
A typical plating cell looks like the following
Can the operator demonstrate to the assessor that they spin the panels 180 degrees half way through the plating cycle to ensure that the plating is even.
Because of the nature of plating, a more even plating is achieved where the panels are rotated half way through the plating cycle, helps top to bottom distribution, so the operator must show the assessor that they carry out this practice.
Can the operator demonstrate to the assessor that they can detect when a panel is over/under plated, i.e. the use of the hole Copper Thickness Measuring scope.
The most important aspect of electrolytic plating is the thickness of copper plated in the hole, too thin and they are scrap too thick and the customer cannot get the component legs in the holes, plus overplating is one of the main reasons for short circuits, therefore the operator must show that they can select the right hole size ( very important as the process are apprx £500 each) and that they can place the probe in the hole to measure the plating thickness and then record the result on the plating chart. Also the operator must state the minimum thickness plated is typically 25um ( unless stated on the job card other wise and they must state where this is)
Because we cannot measure the copper plating thickness in flex (too thin), does the operator understand the reason why we need to microsection, flex to check thickness, plus can the operator demonstrate to the assessor that they can detect by feel that panels are under or overplated, i.e. overplated – higher than the dry film, underplated lower than the dry film.
Because the dry film is 50 microns thick, it is possible to feel if the panel is plated with approx. 40 – 50 microns of copper on the surface, with flex what is plated in the holes is typically plated on the land.
As can be seen from the above section of a panel coming of the plating line, the copper plating (& 5um tin) is practically level with the dry film this would typically produce copper in the holes of 30 microns plus, and as can be seen it is close to level with the dry film but not above, this is our target
If the panel was under plated it would look like the following
Now if the panel was overplated it would look like the following
As you can see the copper is plated level with the dry film, however the tin then plates over the edges of the dry film and will cause resist entrapment, which is the principle cause of short circuits after etch.
Can the Operator demonstrate to the assessor that they can perform the maintenance on the plating connections, and understand the importance a good clean connection.
The operator must show the assessor that they will clean the cathode connections ( plating jig rail) often enough as required to maintain a good connection, this is assessed visually, if the copper rail is oxidised or has copper sulphate salts on this, this needs to be clean with scotchbrite (green pads), and the operator must state to the assessor that where the connection is not clean it may raffect the quality of plating, by increasing the resiatance of the plating connection
Can the operator explain to the assessor the importance of ensuring the water rinses and plating tanks are clean and free from debris.
The plating rinses must be clean and free from debris, debris may get trapped in the hole during the plating process, and affect the plating of the hole.
Can the operator demonstrate to the assessor how to correctly complete the process maintenance record
The operator must demonstrate to the assessor that they understand the importance of process operator maintenance, and that it is their responsibility to ensure this is completed at the right time, it is always done, and that there is a record of all these checks being completed
At this Level – The Operator can run the Plating Line – Whilst having someone else present they can refer to
Can the operator demonstrate to the assessor the plating current calculation from the panel areas.
State Area/side, Total Area, Current Density Used, then Current calculated
Example 100 sq inch on top side, 130 sq inch on bottom side.
230 sq inches = 32 amps for the copper and 32 amps for the tin per panel, with 2 panels per jig then its 64 amps for 80 mins.
What is the purpose of the Pattern Copper Plate process?
The purpose of the pattern plating process is to plate a minimum of 25 microns of copper down the holes ( or as specified on the jobcard), this is to then connect the internal layers if multilayer and to provide enough copper that with withstand the z expansion of the board during the subsequent assembly and soldering of the finished printed circuit.
What is the purpose of the Pattern Tin Plate process?
The tin plating process is to provide an etch resist, to protect the copper of the holes and tracks during the subsequent etching process. This must be thick enough not to be attacked by the ammonicial etching chemistry, which is approx. 5 microns
Give another name for the Pattern Plate process
Other names are Copper Plating, Electrolytic Copper Plating
Can the operator explain microns, thousands of an inch, the conversions, what the thicknesses are, and can the operator compare the thickness he/she is plating to a human hair
A Micron is 1/1000 of a Millimetre
There are 25.4 microns on 1 thou ( 1/1000 of an inch)
A human hair is approx. 75 microns, so the plating of copper is typically 1/3 of the thickness of a human hair
Where is the Procedure / 1 page summary located?
The page 1 summary is displayed at the start of the line
Name the Previous process & the Subsequent process
The previous process to electrolytic plating is the developing operation
The next operation is the resist stripping operation, this is where the dry film is chemically removed, this is an immersion/spraying process.
Describe what the acceptable output from the Pattern Plate process should be, in terms of Finish / Quality
The finish/quality should be of an even finish with no granular deposits or burning of the plated tracks, this should be plated to the thickness specified on the jobcard or to a minimum of 25um in the holes.
The plated copper should be correctly adhered to the electroless copper, this is tested by using a scalpel to test plating adhesion, now adhesion testing tape could be used, but the scalpel test is actually a more aggressive test and should be performed on a feature on the robber bar, the track interface should not separate, if it seperates something is wrong with the precleaning chemistry.
What is the Purpose of the Acid Cleaner
The acid cleaner is there to remove any alkaline developer residues, and also to remove any oxidation or light finger prints prior to the microetching process, the copper must be very clean prior to being microetched
Why is it Critical “not to over etch”, during copper pre-clean?
The electroless copper deposit is very thin, typically 2 microns, and the Microetch could remove the copper, which would then produce voids and scrap the panel, so the Microetch combination of time/temperature and etch chemistry concentration is very important.
Why is it Critical to apply correct plating currents and times?
The correct combination of plating current and plating time is required to produce the correct plating in the holes.
If the plating current is too high for the plating area on the panel, we will get poor plating distribution, and possibly shorts or holes being undersize.
If the plating current is too low we would get too low plating in the holes, leading to panels being scrapped, as copper is too thin.
If the time plated is too short, then there will be too little plating in holes
If the time plated is too long then we will get overplating as above.
What is a possible consequence from “over-plating”? – list 3 items
Resist Entrapment and short circuits
Holes being under sized
If controlled impedance design then signal integrity would be affect
What is a possible consequence from “under-plating”? – list 3 items
Boards will not be able to be soldered correctly
Holes will be oversized
Current carrying capacity of tracks could be too low
What is the purpose of Anodes and why is it important to maintain sufficient Anode mass / area ?
The copper anodes provide the copper that is plated onto the holes via the plating solution, and there must be the right ammount of copper anodes and these anodes must be in the position i.e. within 80% of the plated area of the panel
What do you understand by a “High Current Density area” and what care / precautions should you take?
A high current density area, is sparse tracking, i.e. the plating from the aodes is concentrating on a small area.
The following demonstrates high current density area, i.e. not much tracking, less than 25% of plated area
In comparison to a low plating density area, i.e. a lot of areas to be plated
What is the minimum & preferred copper thickness, and, how do you monitor & record ?
The minimum unless otherwise stated is 25 microns
The preferred is 30 microns
This is monitored by the Cu Scope and record on the plating thickness chart
List 3 aspects that may contribute to rough plating
Chemical Constituents in bath are out of specification
Plating Current too high
Filters blocked and particles are floating in batch
At this Level – The Operator is deemed to be a fully competent plating operator
Can the operator demonstrate to the assessor that they can make up chemical baths.
The operator must then show how the chemical batches such as the acid cleaner and Microetch are made up, the operator must demonstrate they know where the process data sheets are, what the make-up is, the importance of ensuring the bath is analysed after make up to ensure it is within specification.
The operator must also demonstrate where the old spent chemistry is put for disposal. The operator must also be wearing the correct safety equipment, gloves, goggles, lab coat, safety shoes.
The operator must also show that they understand that the heater must be switche doff before emptying bath, and that when empty the batch must be checked to see there are no build up on tank edges or debris in the tank etc..
Can the operator demonstrate to the assessor that they fully understand the workings of the process, and have the necessary process knowledge to fault find issues and provide corrective actions
At this point the operator must now going through each stage of the process, and describe everything above, without referring to this in writing, this must be explained in detail, each stage, covering all of the above.
Then the operator must explain the causes of overplating, and underplating to the assessor.
Can the operator explain the Environmental implications of this process, and how we control the effluent from this process
The operator must now explain that they understand that this is a chemical process that can seriously affect the environment, and that acid & copper is the biggest issue from this process, and that we only have a limit of 3ppm of copper, so even if a small ammount of copper solution got into the water outfall, then this would be a significant environmental issue, this is controlled by our effluent plant.
Can the operator explain the process costings for this process.
A fully competent operator is aware of the following as these affect the process running costs of this process.
Acid Cleaner Cost
Carrier and brightner Cost
Cost of Copper solution make-up
Cost of Carrier and Brightner
Cost of copper Slugs
Cost of Tin Solution
Cost of Tin Slugs
Once the plating operator gets to this point and understands all of the above then this person, once they have operated the line for 6 months, can call themselves a competent electrolytic plating operator.
For the absolute plating expert, they should be able to explain Faradays law of electroplating
Faraday’s Laws of Electrolysis
Before understanding Faraday’s laws of electrolysis, we have to recall the process of electrolysis of a metal sulfate.
Whenever an electrolyte like metal sulfate is diluted in water, its molecules split into positive and negative ions. The positive ions or metal ions move to the electrodes connected with negative terminal of the battery where these positive ions take electrons from it, become pure metal atom and get deposited on the electrode. Whereas negative ions or sulphions move to the electrode connected with positive terminal of the battery where these negative ions give up their extra electrons and become SO4 radical. Since SO4 cannot exist in electrically neutral state, it will attack metallic positive electrode and form metallic sulfate which will again dissolve in the water. Faraday’s laws of electrolysis combine two laws and these are,
Faraday’s First Law of Electrolysis
From the brief explanation above, it is clear that the flow of current through the external battery circuit fully depends upon how many electrons get transferred from negative electrode or cathode to positive metallic ion or cations. If the cations have valency of two like Cu++ then for every cation, there would be two electrons transferred from cathode to cation. We know that every electron has negative electrical charge − 1.602 X 10 − 19 Coulombs and say it is – e. So for disposition of every Cu atom on the cathode, there would be – 2.e charge transfers from cathode to cation. Now say for t time there would be total n number of copper atoms deposited on the cathode, so total charge transferred, would be – 2.n.e Coulombs. Mass m of the deposited copper is obviously function of number of atoms deposited. So, it can be concluded that the mass of the deposited copper is directly proportional to the quantity of electrical charge that passes through the electrolyte. Hence mass of deposited copper m ∝ Q quantity of electrical charge passes through the electrolyte.
Faraday’s First Law of Electrolysis states that only,
According to this law, the chemical deposition due to flow of current through an electrolyte is directly proportional to the quantity of electricity (coulombs) passed through it.
i.e. mass of chemical deposition,
Where Z is a constant of proportionality and is known as electrochemical equivalent of the substance.
If we put Q = 1 coulombs in the above equation, we will get Z = m which implies that electrochemical equivalent of any substance is the amount of the substance deposited on passing of 1 coulomb through its solution. This constant of passing of electrochemical equivalent is generally expressed in terms of milligram per coulomb or kilogram per coulomb.
Faraday’s Second Law of Electrolysis
So far we have learned that the mass of the chemical, deposited due to electrolysis is proportional to the quantity of electricity that passes through the electrolyte. The mass of the chemical, deposited due to electrolysis is not only proportional to the quantity of electricity passes through the electrolyte, but it also depends upon some other factor. Every substance will have its own atomic weight. So for same number of atoms, different substances will have different masses. Again, how many atoms deposited on the electrodes also depends upon their number of valency. If valency is more, then for same amount of electricity, number of deposited atoms will be less whereas if valency is less, then for same quantity of electricity, more number of atoms to be deposited. So, for same quantity of electricity or charge passes through different electrolytes, the mass of deposited chemical is directly proportional to its atomic weight and inversely proportional to its valency.
Faraday’s second law of electrolysis states that, when the same quantity of electricity is passed through several electrolytes, the mass of the substances deposited are proportional to their respective chemical equivalent or equivalent weight.
Chemical Equivalent or Equivalent Weight
The chemical equivalent or equivalent weight of a substance can be determined by Faraday’s laws of electrolysis and it is defined as the weight of that subtenancy which will combine with or displace unit weight of hydrogen. The chemical equivalent of hydrogen is, thus, unity. Since valency of a substance is equal to the number of hydrogen atoms, which it can replace or with which it can combine, the chemical equivalent of a substance, therefore may be defined as the ratio of its atomic weight to its valency.