Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/60—Electroplating characterised by the structure or texture of the layers
  • C25D5/615—Microstructure of the layers, e.g. mixed structure
  • C25D5/617—Crystalline layers
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/38—Electroplating: Baths therefor from solutions of copper
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/18—Electroplating using modulated, pulsed or reversing current
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/60—Electroplating characterised by the structure or texture of the layers
  • C25D5/623—Porosity of the layers
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/22—Secondary treatment of printed circuits
  • H05K3/24—Reinforcing the conductive pattern
  • H05K3/241—Reinforcing the conductive pattern characterised by the electroplating method; means therefor, e.g. baths or apparatus
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/40—Forming printed elements for providing electric connections to or between printed circuits
  • H05K3/42—Plated through-holes or plated via connections
  • H05K3/423—Plated through-holes or plated via connections characterised by electroplating method

Definitions

• This invention relates to improved means for carrying out electrochemical processes, particularly electro- deposition.
• FIG. 1(a) of the accompanying drawings The basic arrangement for a typical elect rode position process is shown diagrammatically in Figure 1(a) of the accompanying drawings, in which a source of electrical power is shown at 1. This is most commonly a transformer-rectifier but may alternatively be a battery or a rotary generator. Means for varying the output voltage are provided.
• the current source 1 is connected to a workpiece 2 and another electrode 3 which are suspended in a cell or bath 4 of electrolyte solution forming an electrolytic cell.
• a reversing switch unit 5 is interposed between the power source 1 and the cell 4.
• the unit 5 may be a number of switches operated mechanically, appropriate electromechanical relays or solid state devices.
• the unit 5 operates at intervals, producing the effect shown in Figure 1(b), which is a graph of the voltage applied to the cell against time.
• the normal voltage V is replaced at intervals by the same voltage in the opposite sense.
• FIG. 2(a) Another known technique is "Pulse Plating".
• the basic arrangement is shown diagrammatically in the accompanying Figure 2(a). It is the same as that of Figure 1(a), except that a pulsing unit 6 replaces the switch unit 5.
• the unit 6 periodically interrupts one or both of the connections between the power source 1 and the cell but does not reverse them. This produces the effect shown in Figure 2(b), again a graph showing the relationship between voltage applied to the cell and time.
• a fairly high frequency is required, up to 5,000 cycles per second or more and the only suitable construction for the unit 6 is a solid state device, such as an array of field-effect transistors which may be controlled by a microprocessor.
• Pulse plating can have various beneficial effects. It can refine the crystal structure of the deposit, reduce its porosity or stress, or improve throwing power.
• the facility for varying the voltage of the source 1 can be retained and further control of the process is usually provided by adjustment of the frequency at which the unit 6 "chops" this supply or the proportion of each cycle for which it is “on” or “off", that is, the "mark-space ratio".
• electrolytes used for electrodeposition purposes generally contain, apart from appropriate metal ions, organic additives which are there for the specific purpose of modifying the structure and/or brightness of the metal deposit. These additives are usually adsorbed or diffused onto the deposit surface and cause changes in deposit structures some of which are not always desirable.
• the object of the invention is to improve the performance of an electrochemical process, more particularly - but not exclusively - electrodeposition.
• a method of operating an -electrochemical process comprises the application of at least two independently-controlled voltages in alternation. It will be evident that if more than two independently-controlled voltages are utilised they will be applied cyclicly. Preferably, one of the two or more voltages will be reversed. Alternatively one of the voltages may modulate the other or another voltage. One or each voltage may be pulsed.
• Another aspect of the present invention is the provision of equipment for operating an electrochemical process comprising at least two independently-controlled electrical power sources and switching means for applying them in alternation.
• the switching means could be adapted to apply more than two independently-controlled voltages cyclicly.
• the switching means is adapted to reverse one of the two or more applied electrical power sources.
• the switching means is adapted to cause one electrical power source to modulate the other or another.
• the switching means may also be adapted to pulse one or each electrical power source.
• a third aspect of the invention is the provision of an electrolyte for enhancing the process as operated in accordance with the invention, the electrolyte comprising at least two organic additives, at least one being a polariser the effects of which are inhibited by reverse voltages, and the other being a depolariser that is preferentially adsorbed.
• a basic arrangement of equipment in accordance with the invention is shown diagrammatically in Figure 4(a) of the accompanying drawings.
• the unit 9 switches in the source 8 to modulate the output from source 7.
• Figure 5 shows a typical control arrangement for such a unit.
• the control unit is normally capable of producing pulses of frequency and mark-space ratio which are independently adjustable for each supply and for adjustable periods before switching from one to another.
• the programme may provide for more than one such setting for either or both supplies.
• Several different voltages may be applied to the cell in each direction, in which case the control unit may need to provide for connection to more than two power supplies.
• An example of the use of such a facility would be a requirement for the pulsed voltage to fall not to zero but to some other value •'during each pulse.
• the settings of the control unit or the voltages of the power supplies may be arranged to vary with time or with total current passed so as to provide optimum conditions at various stages of a process.
• Electrodepo sited copper is used to provide electrical conduction in through holes used for component connection and for connection between surfaces and intermediate layers.
• the conventional, process employs an aqueous electrolyte of copper sulphate and sulphuric acid to which are usually added chloride ions and organic additives to assist with anode dissolution and to give deposits with suitable mechanical properties.
• the current distribution on many boards makes it very difficult to deposit sufficient copper on some parts of the board, eg. high aspect ratio through holes, without excessive thicknesses on other areas, eg. fine tracks and isolated pads. This in itself causes problems with dry film solder resists applied at a subsequent stage.
• the electrolyte comprises an acid copper sulphate solution containing high molecular weight polyethers, sulphur propyl sulphides and chloride ions which together change the polarisation characteristics of the solution at different current densities thus effecting an improvement in the distribution of copper over complex shapes such as printed circuit boards. It is true that the above additives, singly or together, have little or no beneficial effect on the distribution of copper when using direct current. It is also true that singly these additives have no effect on distribution when using pulsed or differential pulse reverse current.
• the polarisation of the cathode is primarily effected by adsorption of the polyether and sulphide.
• diffusion effects of the sulphide become dominant.
• the polyether has an inhibiting effect on the deposition of copper and the sulphide has a depolarising (stimulating) effect which is therefore diminished at higher current density areas giving an overall improvement in metal distribution.
• the acid copper solution which forms part of the invention preferably contains: Copper Sulphate 10 - 350 g/1
• R is a sulphur containing group eg. mercapto propane sulphonic acid Polyether HO - (CH 2 - CH 2 - 0) n - (CH 2 - CH - 0) m - R (10 - 70ppm)

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Crystallography & Structural Chemistry (AREA)
• Electroplating Methods And Accessories (AREA)
• Hybrid Cells (AREA)

Applications Claiming Priority (2)

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• 1988
  • 1988-01-27 GB GB888801827A patent/GB8801827D0/en active Pending
• 1989
  • 1989-01-18 AU AU29471/89A patent/AU2947189A/en not_active Abandoned
  • 1989-01-18 WO PCT/GB1989/000042 patent/WO1989007162A1/en not_active Application Discontinuation
  • 1989-01-18 EP EP89901720A patent/EP0396610A1/en not_active Withdrawn
  • 1989-01-18 GB GB8901091A patent/GB2214520A/en not_active Withdrawn
  • 1989-01-26 ES ES8900270A patent/ES2010390A6/es not_active Expired

Non-Patent Citations (1)

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