Classifications

• • 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
  • H05K3/10—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern
  • H05K3/12—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using thick film techniques, e.g. printing techniques to apply the conductive material or similar techniques for applying conductive paste or ink patterns
  • H05K3/1216—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using thick film techniques, e.g. printing techniques to apply the conductive material or similar techniques for applying conductive paste or ink patterns by screen printing or stencil printing
  • H05K3/1233—Methods or means for supplying the conductive material and for forcing it through the screen or stencil
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K3/00—Tools, devices, or special appurtenances for soldering, e.g. brazing, or unsoldering, not specially adapted for particular methods
  • B23K3/06—Solder feeding devices; Solder melting pans
• • 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
  • H05K3/30—Assembling printed circuits with electric components, e.g. with resistor
  • H05K3/32—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits
  • H05K3/34—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by soldering
  • H05K3/3457—Solder materials or compositions; Methods of application thereof
  • H05K3/3485—Applying solder paste, slurry or powder
• • 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
  • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
  • H05K2203/01—Tools for processing; Objects used during processing
  • H05K2203/0104—Tools for processing; Objects used during processing for patterning or coating
  • H05K2203/0134—Drum, e.g. rotary drum or dispenser with a plurality of openings
• • 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
  • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
  • H05K2203/11—Treatments characterised by their effect, e.g. heating, cooling, roughening
  • H05K2203/1105—Heating or thermal processing not related to soldering, firing, curing or laminating, e.g. for shaping the substrate or during finish plating

Definitions

• the present invention is directed to a technique for multipoint dispensing of viscous materials and more particularly, to a method and an apparatus for multipoint dispensing of solder paste for surface mounting of chip carriers on circuit boards.
• the quantity of solder deposited should not be excessive to avoid an electrical short between two adjacent solder joints.
• an alternative method for depositing solder paste on PWB's is a technique using a multipoint dispensing tool comprising a hollow chamber having a multiorifice nozzle attached at one end thereof.
• the nozzle orifices are spaced to match the PWB footprint pattern and the corresponding chip carrier lead geometry.
• Some of these problems include the poor control of the volume and geometry of the dispensed solder paste, clogging of the orifices of the nozzle, variations in the paste viscosity, and difficulty in achieving uniform paste distribution among the orifices due to paste crust and/or void formations within the dispensing tool.
• a method for multipoint dispensing of viscous material onto a board comprises positioning a viscous material dispenser having a plurality of orifices at a predetermined distance from the board; during a first time interval, increasing the pres ⁇ sure within the dispenser to a predetermined value thereby forcing viscous material out of the dispenser orifices onto the board? moving the dispenser, at the end of the first time interval, relative- to the board at a substantially constant velocity while maintaining the dispensing pressure substantially at said predetermined value for a predetermined second time interval; and removing the pressure within the dispenser at the end of the second time interval.
• Another embodiment of the invention comprises the steps of placing a supply container of solder paste in transfer relationship with the top portion of the dispensing tool; applying vacuum to two regions of the dispensing tool thereby pulling solder paste out of the supply container into the dispensing tool; vibrating the dispensing tool for a first predetermined time period substantially along its axial direction while the vacuum is applied; and removing the vacuum while maintaining the vibration of the dispensing tool for a second predetermined time period.
• a further embodiment of the invention relates to a method for handling solder paste within a solder paste dispensing tool which comprises covering the top surface of the paste within the tool with a liquid seal for preventing crust layer formation therein.
• a method for handling solder paste within a multiorifice paste dispensing tool comprises placing the orificed portion of the dispensing tool, when not in use, in a container including a liquid seal material for preventing the paste in the orifices from drying.
• a still further embodiment of the invention is directed to a method for controlling the viscosity of solder paste within a multiorifice solder dispensing tool comprising the steps of monitoring the temperature within the tool; and circulating a flow of heating fluid proximate to the exterior surface of the dispensing tool in response to the temperature monitoring step.
• FIG. 1 shows a known multipoint solder paste dispenser
• FIG. 2 is a perspective schematic representation of the interior of a multipoint dispensing nozzle in
• FIGS. 3A and 3B show time diagrams of the dispensing parameters in accordance with one embodiment of the invention.
• FIG. 4 illustrates a solder paste loading technique in accordance with another embodiment of the invention.
• FIG. 5 schematically shows a technique for preventing paste crust formation in accordance with a further embodiment of the invention.
• FIG. 6 illustrates the effect of temperature on solder paste viscosity
• FIG. 7 illustrates a technique for controlling the viscosity of the solder paste according to a still further embodiment of the invention.
• Viscous materials of a type having a dispense viscosity ranging from about 2x10 cps to about 2x10 cps at 1 sec shear rate may be dispensed using the teachings described herein.
• adhesives e.g., conductive as well as nonconductive epoxies
• silicones e.g., Room Temperature Vulcanizing (RTV) Silicone
• rubbers e.g., Rubbers, and/or other viscous materials widely used in the electronic industry.
• reference numeral 10 indicates a multi ⁇ point solder paste dispenser of the type described in the above-referenced paper by D. Schoenthaler (see FIG. 5 thereof).
• the dispenser 10 comprises a generally cylin- drical hollow cartridge 11 adapted to receive solder paste to be dispensed on a printed wiring board (PWB) 12.
• PWB printed wiring board
• a nozzle 13 having a plurality of openings 14 is attached at
• the openings 14 are located along the periphery of the nozzle 13 and are spaced and shaped to substantially match a plurality of bond sites 16 on the PWB 12.
• pressurized air is supplied thereto to force solder paste out of the openings 14 of the nozzle 13 onto the bond sites 16 of the PWB 12.
• FIG. 2 Shown in FIG. 2 is an inside perspective view of a nozzle 20 according to an illustrative embodiment of the invention.
• the nozzle 20 has a flat bottom face 21 with a plurality of openings 22 arranged in a predetermined pattern.
• the openings 22 are dimensioned and spaced to substantially correspond to the metallized terminations of a chip carrier (not shown) to be mounted on a board 23.
• a plurality of. bond sites 24 having a pattern substantially identical to that of the nozzle openings 22. Alignment of the openings 22 with the bond sites 24 may be achieved by using any well known alignment technique, such as that described in U.S. Patent 4,295,596.
• the nozzle 20 is adapted to be connected at one end of a cylindrical solder paste cartridge 25 comparable to the cartridge 11 of FIG. 1.
• the solder paste may be selected from known commercially available types commonly used in the electronics industry.
• a pyramid shaped diverter 26 Positioned within the nozzle 20 is a pyramid shaped diverter 26 for directing the paste flow towards the openings 22. The diverter 26 prevents stagnation of the paste in the central portion of the nozzle 20 while, at the same time, reducing the volume of paste needed to fill the nozzle 20 and the cartridge 25.
• a solder paste dispensing sequence will be described with reference to FIGS. 2, 3A and 3B.
• the nozzle 20 and the board 23 are moved relative to each other, and are positioned at a predetermined initial distance, ., from each other.
• the initial distance, ⁇ is shown in FIG. 2 as being different from zero, the present teachings are also applicable when the surface 21 of the nozzle 20 and the board 23 are initially in contact with each other.
• pressurized air is supplied to the dispensing tool (i.e., to the cartridge 25 and the nozzle 20 attached thereto) forcing paste out of the orifices 22 onto, and in adherence with, the bond sites 24 of the board 23 thus closing the initial gap, if any, between the bottom face 21 of the nozzle 20 and the board 23.
• the dispensing tool (including the nozzle 20 and the cartridge 25) is moved upwards and away from the surface of the board 23 at a predetermined substantially constant velocity, V.
• V substantially constant velocity
• the dispensing tool While the dispensing tool is .moving away from the board 23, the dispense air pressure, P, remains substantially constant and is terminated at time t2 « The dispensing nozzle 20 continues to move upwards causing the paste adhering to the board 23 to separate from the nozzle openings 22 thus leaving deposits on the bond sites 24 of board 23.
• these process parameters include the initial gap, ⁇ ; the dispense pressure P, the tool velocity V and the time periods t ⁇ and t ⁇ .
• the initial gap ⁇ is of the order of 0.0 to 0.25 mm, the higher end of such range allowing for board warpage;
• the dispense pressure P ranges between 0.07 and 0.7 kg/cm 2 ;
• the range of the tool velocity V is between 12.7 and 127 mm/minute;
• the delay time t ⁇ is of the order of 0.1 to 0.5 sec; and the dispense time t2 is typically between 0.2 and 1.0 sec.
• the preferred corresponding dispense UR£A time t2 is selected in a range between 0.2 and 0.4 sec. If the delay time t- j is a longer one, e.g., of the order of 0.5 sec, the preferred dispense time t2 is set between 0.65 and 1.00 sec.
• One condition to be maintained for the selection of the two time periods t ⁇ and t2 is that the latter is always larger than the former in order to permit the paste to be fed out of the nozzle as the latter retracts.
• SOLDER PASTE LOADING An important aspect of solder paste dispensing is the method used to load solder paste into the dispensing cartridge and nozzle assembly.
• FIG. 4 schematically illustrates a method and an apparatus for loading paste into the dispenser cartridge and nozzle in accordance with an embodiment of the invention.
• Solder paste is placed in a supply container 40 where it is warmed by being mixed vigorously without introducing additional air or changing the character of the paste itself. Heat is applied if necessary to elevate the paste temperature to about 38-49°C.
• the supply container 40 is coupled to one side of an adaptor plate 41 which in turn is located on top of a dispensing cartridge 42 to be loaded or filled with solder paste.
• a first seal 43 is located around a neck portion 44 of the adaptor plate 41 to prevent leaks between the supply container 40 and the adaptor plate 41.
• a second seal 46 is positioned between the top portion of the dispensing cartridge 42 and the adaptor plate 41.
• a wire screen 45 is positioned proximate to the bottom of the supply container 40 for filtering semirigid paste and crust particles out of the paste prior to its transfer into the dispensing cartridge 42.
• the neck portion 44 of the adaptor plate 41 comprises at least one hole 48 for allowing paste to be transferred from the supply container 40 into the dispensing cartridge 42.
• an array of small diameter holes (such as holes 48) is formed in the neck portion 44 of the adaptor plate 41.
• the latter further comprises an elongated chamber 49 for coupling a vacuum source (not shown) to the top portion of the dispensing cartridge 42.
• the bottom portion of the dispensing cartridge 42 comprises a multi-orifice nozzle 51 attached thereto.
• the nozzle 51 is of a type described above in connection with FIG. 2.
• the dispensing tool including the cartridge 42 and the nozzle 51 is placed on a loading station 52 which comprises a loading table 53 and a supporting body 54.
• Body 54 comprises, in a recessed portion thereof, a seal 56 adapted to mate with the periphery of the nozzle 51.
• a filtering arrangement comprising a filter member 58 supported by a porous member 59, such as a metal screen or a rigid plate having a plurality of holes therethrough.
• the filter member 58 may be, for example, a sheet of filter paper.
• the filter member 58 includes a rough- surfaced rubber pad positioned within the opening 57 of the supporting body 54 such that its top rough surface is in slight contact with the bottom flat face of the nozzle 51.
• the supporting body 54 further comprises an elongated conduit 60 for coupling a source of vacuum (not shown) to its central opening 57.
• the vacuums applied via chamber 49 and conduit 60 are held constant while paste is pulled into the dispensing cartridge 42.
• the vacuums are maintained while the loading table 53 is vibrated up and down in the axial direction of the cartridge 42 as illustrated by bidirectional arrow 62.
• the table 53 would be vibrating during an initial period of about 20 seconds with vacuums applied.
• the vibration of the table 53 is continued for an additional period of about 10 seconds.
• the use of a rough-surfaced rubber pad as a filter member 58 is advantageous in that grooves in the rough surface permit each nozzle opening to be filled by the vacuum pulled, through conduit 60, from under the screen 59. The foregoing causes a complete filling of the nozzle 51.
• solder paste used for dispensing dries slowly
• solder paste dispenser remaining idle for about one hour will become clogged and useless as paste dries at the nozzle orifices and on the surface internal to the dispensing cartridge.
• FIG. 5 schematically illustrates a technique for preventing the paste from drying and forming a crust layer in accordance with another illustrative embodiment of the invention.
• a dispensing cartridge 70 with a multi-orifice nozzle 71 attached thereto, contains a volume of solder paste 72 to be dispensed.
• pressurized air is applied to the top portion of the cartridge 70 to force the paste 72 out of the orifices of the nozzle 71.
• a floating piston 73 is positioned within the cartridge 70 above the paste 72.
• the piston 73 is preferably tapered and sized to influence self-centering and prevent an air blow through in sections of lower paste viscosity.
• a liquid 74 is applied around the floating piston 73 and acts as a liquid seal.
• the nozzle 71 is preferably lowered into a small dish 76 containing a liquid seal 77 thereby preventing paste in the orifices of the nozzle 71 from drying.
• Liquids such as commercially available wave soldering oils and/or fluorinated hydrocarbon materials may be used for the liquid seal 74 and the liquid 77 contained in the nozzle dish 76.
• DISPENSING VISCOSITY CONTROL DISPENSING VISCOSITY CONTROL
• the temperature of the paste during dispensing is one of the variables affecting - li ⁇
• d __i>spensing results most commercial solder pastes exhibit a substantial reduction in viscosity with a relatively small increase in temperature (e.g., between -9° and -7°C) as illustrated in FIG. 6.
• consistent dispensing results can be achieved by adequately controlling the viscosity of the paste by monitoring and controlling the paste temperature and maintaining it at a control temperature, T , above the usual ambient temperature range.
• FIG. 7 schematically shows an arrangement for controlling the viscosity, and hence the temperature, of the paste 80 within a dispensing cartridge 81.
• a jacket sleeve 82 is attached to a dispensing assembly support plate 83 and shaped such that a gap 84, formed between the sleeve 82 and the cartridge 81 , surrounds the dispensing cartridge 81.
• a temperature sensitive control device 86 is attached to, and through, the support plate 83 to enable the monitoring of the temperature within the dispensing cartridge 81.
• the warm fluid exits the gap 84 at the bottom of the sleeve 82 thereby keeping the paste 80 within a predetermined temperature range in response to the temperature sensitive control device 86.
• a low flow of warm air supplied to the fluid conduit 87, keeps the paste 80 at a desired temperature.
• the heating mechanism in FIG. 4, which is symbolically represented by reference numeral 61, may include a sleeve and warming fluid arrangement of the type described in FIG. 7.
• a warm air flow around the dispensing cartridge 42 of FIG. 4 would maintain the solder paste within prescribed temperatures during the cartridge loading operation.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Mechanical Engineering (AREA)
• Coating Apparatus (AREA)
• Electric Connection Of Electric Components To Printed Circuits (AREA)

Applications Claiming Priority (1)

Publications (1)

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• 1984
  • 1984-07-18 EP EP84902982A patent/EP0187746A1/de not_active Withdrawn
  • 1984-07-18 JP JP59502923A patent/JPS61502734A/ja active Pending
  • 1984-07-18 WO PCT/US1984/001123 patent/WO1986000842A1/en unknown

Non-Patent Citations (1)

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