Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B3/00—Drying solid materials or objects by processes involving the application of heat
  • F26B3/02—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air
  • F26B3/04—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour circulating over or surrounding the materials or objects to be dried
• • 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
  • H05K3/227—Drying of printed circuits

Definitions

• the present invention relates to improvements made to machines for drying wired printed circuit boards after cleaning them after an automatic welding operation of the components, comprising: a tunnel in which the boards can be moved dry, this tunnel having an inlet for wet cards and an outlet for dried cards; means for circulating, in the tunnel, drying air in the opposite direction to the direction of movement of the cards, that is to say from substantially the exit from the tunnel to substantially the entrance to the tunnel; and regulating means for increasing the temperature of the drying air between its injection into the tunnel and its extraction from the tunnel. Drying machines designed for this specific function are already known, which have many drawbacks by limiting use.
• the volume of air used for drying is very large, of the order of 10,000 m 3 per hour.
• the production facilities for wired printed circuit boards and in particular drying machines
• the large volume of air displaced in these rooms by the drying machines is completely incompatible with correct operation of the air conditioning: this air conditioning is therefore constantly disturbed, which consequently adversely affects the operation of the various machines of the printed circuit board processing installation.
• the object of the invention is essentially to remedy, as far as possible, the drawbacks of the drying machines used at present and to provide an improved drying machine which better meets the various requirements of the technique, in particular thanks to a machine arranged in such a way that its operation in an air-conditioned room does not disturb the air conditioning and whose operating cost as well as the manufacturing cost are as low as possible.
• the drying machine according to the invention is characterized in that the regulation means include:
• drying air heating means distributed along the tunnel and arranged to bring the drying air to increasing successive temperatures, the relative humidity of the drying air remaining between two predetermined values ;
• the temperature of the air, at its injection into the tunnel is between ambient temperature and 50 ° C.
• the temperature of the air, at its extraction from the tunnel is lower than 90 ° C., preferably of around 80 ° C, and the relative humidity of the air in the tunnel remains between about 40% and 60%.
• the relative humidity of the drying air therefore presents, throughout the tunnel, variations of small value (of the order of 20%), sufficient to provide effective drying.
• blowing means are provided for blowing air on the cards in the direction opposite to their direction of movement, which is eliminated. a large part of the cleaning liquid flowing on said cards. It follows that the cards thus previously cleared of the game dripping cleaning liquid ("spin" phase) are simply wet when they approach the actual drying part of the machine, which allows increased energy savings.
• the machine of the invention further comprises heat exchanger means between the hot and humid air extracted from the tunnel in the vicinity of the entrance thereof and the fresh air introduced into the tunnel in the vicinity of the exit from it. This results in a condensation of the water vapor contained in the hot air coming from the tunnel before the air is released to the outside.
• the water thus recovered can be returned to the final rinsing tank of the card washing zone in the cleaning machine associated with the drying machine of the invention and located upstream thereof. This saves cleaning water and avoids the problems posed by the condensation of water in chimneys.
• the fresh air absorbed by the installation with a flow rate equal to that of the exhaust air is preheated in the exchanger: its relative humidity is lowered and the overall efficiency is increased.
• the drying machine of the invention is satisfied with a very low flow rate of fresh air, for example of the order of 500 m 3 per hour in the case previously considered, which is compatible with efficient air conditioning of the local.
• FIG. 1 is a schematic perspective view of a drying machine arranged in accordance with the invention.
• FIG. 2 is a graph illustrating the operating mode of the drying machine of Figure 1.
• the drying machine for wired printed circuit boards, shown in Figure 1 comprises a tunnel 1, which can be rectilinear as shown or marry any curved contour appropriate to the needs, inside which a transporter 2 extends from the entrance 3 of the tunnel, through which the wet cards 4 penetrate, to the exit 5 of the tunnel at which appear dried cards.
• the conveyor 2 can be specific to the tunnel and be connected to processing stations located downstream and upstream by other means for moving the cards 4, in particular by other carriers.
• the conveyor 2 can also be the same as that which moved the cards within and from the cleaning machine (not shown) located upstream of the drying machine.
• a turbine 6 Downstream of the inlet 3 is a turbine 6 which propels air onto the cards 4 via a nozzle 7 of vertical shape and inclined towards the inlet 3 of the tunnel, so that, under the action of the jet of air propelled against the flow of the cards 4, the cleaning liquid dripping on the faces of the cards is discharged in the direction of the inlet 3 ("spin" operation).
• the tunnel 1 Downstream of the blowing nozzle 7, the tunnel 1 is provided with partitions 8 separating its internal volume into a succession of chambers 9.
• These partitions are arranged to be easily passable by the cards 3 driven by the transporter 2, but to constitute barriers to air flow; they can advantageously be formed by two half-barriers constituted by elastically deformable strips (for example made of rubber). Only three of these partitions are visible in Figure 1.
• each partition 8 means are provided for authorizing the passage of air from one room to the adjoining room: for this purpose, two openings 10 are made in the side wall of the tunnel, on either side another of partition 8, and therefore opening into two adjoining rooms.
• a housing 11 covers the two openings 10 and contains air heating means (for example a thermostatically controlled electrical resistance 12) intended to heat the air passing from one room to the next through the openings 10 and the interior volume of the housing 11.
• air heating means for example a thermostatically controlled electrical resistance 12
• each housing 11 there is provided a fan (not visible in the figures) ensuring local displacement of the drying air. Each fan takes the air in the tunnel 1 through one of the openings 10 and returns it in this tunnel through the other opening 10 after having brought it into contact with the heating means.
• the tunnel 2 is provided with an air inlet mouth 13 which opens in the last chamber 9, in the vicinity of the outlet 5 of the tunnel and an air outlet mouth 14 which s opens in the first chamber 9 located just after the inlet '3 of the tunnel and downstream of the blowing nozzle 7 (these different relative positions being indicated by considering the direction of circulation of the cards 3, symbolized by the arrow 15).
• the air outlet mouth 14 is connected to a plate heat exchanger 16, provided, at its lower part with a tank 17 for collecting condensation water which is connected, by conduits 18, to a point evacuation of these waters; for example, these conduits can transfer the condensation water (of "distilled water” quality) to the card cleaning machine located upstream, in certain types of installation which will be indicated later.
• the exchanger 16 also includes an evacuation 19 of the hot air which is sucked in by a turbine 20 and discharged at 21 to the outside after having given up its calories.
• the exchanger 16 is also provided with an intake 22 of fresh air (ambient air) which is connected to the inlet mouth 13 and set in motion by a turbine 23.
• fresh air ambient air
• the air temperature in degrees Celsius is plotted on the ordinate and the mass of water vapor per unit weight of drying air in g / kg of air is plotted on the abscissa.
• the inclined straight lines 25 are the isotherms and the curves 26 are the curves with constant relative humidity of the air.
• the fresh air at room temperature (of the order of 20 ° C. for example) and at a normal relative humidity of the order of 60% - segment 27, in FIG. 2 - is drawn into the exchanger 16 through the mouth 22 and heats up in contact with the heat exchange plates, heated by the hot air coming from the extraction mouth 14.
• the temperature of the fresh air can reach 40 ° C to 50 ° C (segment 28 in FIG. 2), its humidity level then being reduced to approximately 205. ie approximately 8.6 g of water vapor per kilogram of air.
• This dry and lukewarm air is then sent, via the inlet mouth 13, to the last chamber 9 of the tunnel 1, in which the cards 4 already arrive practically dry.
• the air is enriched with vapor water (segment 29 in Figure 2) until it rushes into the last housing 11; it then contains approximately 28.6 g of water vapor per kilogram of air and its relative humidity is approximately 60%.
• the air in contact with the electrical resistance, the air is heated and its temperature goes from 40 ° C to about 48 ° C, its water vapor content remaining constant and its degree of relative humidity then being reduced to approximately 40% (segment 30 in FIG. 2).
• the air then exits from the last box 11 and then scans the penultimate chamber 9 in which the cards 4 are still wet. At its constant temperature of 48 ° C, the air licks the cards by taking hold of part of their humidity.
• the water vapor content of the air then increases to around 44 g / kg of air and its relative humidity level increases to h. 60 fo (segment 31 in Figure 2), when it rushes into the penultimate housing 11; there, it is heated, its temperature going from 48 ° C to about 56 ° C, and its relative humidity is reduced to 40 f> (segment 32 in Figure 2). Then it enters the previous chamber 9 and the cycle continues, the air being heated and enriched in water vapor in stages, while maintaining a relative humidity level between 40.% and 60%. Finally, on leaving the first housing 11, the air heated to 80 ° C.
• the hot and humid air is then led to the plate exchanger where it transfers part of its heat to the fresh air sucked in through the mouth 22. Due to this cooling, the water vapor condenses and the water is collected in the tank 17. The air is then discharged outside by the turbine 20.
• the drying of the cards 4 in the tunnel 1 is therefore carried out by displacing a current of hot air in the opposite direction the circulation of the cards, so that the wet cards are licked by very hot and very humid air, while the practically dry cards are licked by the relatively not very hot, but relatively dry air.
• the air is never brought to very high temperatures (its temperature remains at most equal to 80 ° C), which avoids excessive consumption of electrical energy for its heating.
• the presence of the dividing partitions 8 avoids aerolic shunts and makes it possible to design the tunnel in a particularly collected form, without loss of efficiency.
• the drying machine according to the invention finds a particularly advantageous application in installations for the production of wired printed circuit boards known as "online installations". It can in particular be incorporated into modern high speed processing installations. cards (of the order of 3 m / min) in which the soldering of the electrical components on the. cards are made with a water-soluble flux solder: it is then possible to recover the condensation water (of "distilled” quality) in the tank 17 of the heat exchanger and to send it back to the washing of the card cleaning machine located downstream.
• the invention is in no way limited to those of its modes of application and embodiments which have been more especially envisaged; on the contrary, it embraces all its variants.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Microbiology (AREA)
• Manufacturing & Machinery (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Drying Of Solid Materials (AREA)
• Electroplating Methods And Accessories (AREA)

Applications Claiming Priority (2)

Publications (1)

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ID=9256892

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Citations (4)

• 1981
  • 1981-04-01 FR FR8106569A patent/FR2503524A1/fr active Granted
• 1982
  • 1982-03-16 JP JP50105782A patent/JPH0233797B2/ja not_active Expired - Lifetime
  • 1982-04-01 JP JP50113282A patent/JPS58500452A/ja active Pending
  • 1982-04-01 DE DE19828209397 patent/DE8209397U1/de not_active Expired
  • 1982-04-01 WO PCT/FR1982/000061 patent/WO1982003523A1/en unknown

Patent Citations (4)

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