DE3913585A1 - Heat treatment system for soldering circuit boards - has boards transferred by continuous feeding in cassettes through heating system - Google Patents

Abstract

The heat treatment system has a pair of conveyor belts (8, 9) used to handle the bases (2) and cover (1) of cassette housings in which the boards (13) are processed. An untreated board is entered ionto the lower half of the cassette which is moved to the heat treatment stage (4), where the cover is inserted and exposive to infra red (5) takes place. The system moves at a rate appropriate to the soldering process. Finished boards are discharged (14). ADVANTAGE - Provides increased productivity in circuit board processing.

Description

The invention relates to a device for heating handling of workpieces according to the preamble of the patent Proverb 1. With such a facility Materia lien or workpieces hardened, dried, soldered, annealed, baked or some other heat treatment be subjected.

For some years now, the SMD (Surface Mounted Device) technology implemented. Here components such as resistors, condensates gates or transistors of an assembly preferably through fully automatic assembly process on one surface placed on a board, i.e. surface mounted and on finally soldered to the board. With the reflow soldering the solder is applied as a paste to the soldering areas, cured and then preferably by convection heat and / or infrared rays melted. Infrared systems operating according to the reflow system are usually continuous systems, in their heat treatment section a given one, each from the component's own dependent temperature profile is set, to prevent the components from thermal overheating protect. To form a perfect solder joint  the inert gas can be flushed through the heat treatment zone, so that the atmospheric oxygen in the heat treatment zone ver is pushing.

With such a continuous furnace, a new batch is ver works, the heat treatment room must be installed Production at the temperature suitable for the new batch profile. During this heating up period no boards are soldered. Because the pick and place machines preferably in a production line with the continuous furnace stand, the productivity of the entire system is determined by significantly reduce the downtime of the continuous furnace device. Such a continuous furnace is only for large lots sizes can be used with satisfactory productivity.

The invention has for its object a device to create heat treatment that is simple new production conditions is adaptable and the increase productivity.

This object is according to the characterize solved the features of claim 1.

By using several closed according to the invention NEN, two-part cassettes can be heated Masses and the heat losses when heating up and during the Reduce production to a minimum and therefore inside the cassettes very quickly a change in Temperaturpro set fils. The closed heat treatment room each the cassette is advantageously by an upper and a lower part is formed, which in turn consists of several parts can exist. Leave to open the heat treatment room the parts advantageously stand out from one another. Ge according to claim 3, the upper and lower part can also ge be flexibly connected to each other. The invention Cassette can also be further developed in that  the cassette parts during opening and closing a guide are engaged with each other. By the closed cassette systems are the operating conditions during the soldering process on the inside of the cassette easy to detect and control because of the heat treatment is not affected by environmental influences and the workpiece is arranged stationary in the cassette. The actual soldering process can be precisely controlled with which the quality of the solder joint is evened out and thus improving the productivity of the entire soldering system becomes. Using multiple cartridges allows one circumferential, continuous soldering process, which takes place without Intermediate storage of the boards directly to the assembly kung can connect.

A particularly effective structure of the subject matter of the invention results if, according to patent claims 2, 5, 6 Device used to open and close the cassettes is, the device according to claim 8 preferred is operated continuously.

An advantageous development of the device according to claim 9 enables the necessary for soldering the circuit boards time-dependent temperature profile in each cassette separately adjust. This way, a cassette can be quickly be adjusted to new operating conditions while another cassette still under the original operating operating conditions.

Are expedient according to claim 10 on the cassettes Connections for introducing inert gas into the closed Cassettes are provided, which low during the soldering process Inert gas losses are guaranteed.  

Batches can be made with the cassette system according to the invention with small lot sizes without due to changes in operations downtimes caused by conditions and with minimal Soldering inert gas losses, which is a step towards In-time production, with minimum lot sizes ("lot size 1") is possible.

Further advantageous developments are the subject of other claims.

Embodiments of the invention are described below of the drawings explained in more detail. Show it:

Fig. 1 is a schematic representation of a first exemplary embodiment of the invention and

Fig. 2 is a schematic representation of a second exemplary embodiment of the invention.

As shown in FIG. 1, a cassette from an upper part 1 and a lower part 2, which in turn may consist of several parts. These each preferably have a rectangular base area with a circumferential peripheral edge projecting on one side. Both parts of the cassette touch in the closed state along the protruding circumferential edge 3 , a heat treatment space 4 which is sealed towards the outside being formed in the interior of the cassette. A plurality of infrared radiators 5 , which are spaced apart from one another, are provided in the peripheral edge, via which the heat treatment room 4 is heated, the temperature profile of which can be controlled as a function of time.

In addition, the cassette parts 1 , 2 are connected to an inert gas source, not shown here. The workpiece 6 , that is, the assembled circuit board is arranged in the cassette relative to the heat treatment chamber 4 . With this construction, contact-free pyrometers can advantageously be used for temperature measurement, which pyrometers must be stationary relative to the measuring point, ie such a high-precision temperature sensor cannot be used in a conventional continuous furnace. The operating conditions (for example cooling, heating speeds, temperature profile) inside the cassette can be influenced by a control unit assigned to the latter, which can be programmed to the respective operating conditions via a central computer.

In the first embodiment shown in FIG. 1, a plurality of upper and lower parts 1 , 2 are attached to a device 7 for opening and closing the cassette. The device 7 contains two circulating conveyor belts 8 , 9 , each with a straight transport section 10 and two deflection sections 11 . The conveyor belts are arranged one above the other, whereby the two straight transfer sections 10 face each other in a closing portion 12 in predetermined parallel spacing and the transformants port belts 8, 9 in opposite directions in the direction of arrow A or B being driven are. The upper conveyor belt 8 supports the upper parts 1, while the lower conveyor belt 9, the lower parts 2 of the cassette bears, said cartridge parts 1, 2 each at the same distance on the conveyor belts 8, 9 are arranged. The number of cassettes is advantageously selected as a function of the operating parameters, so that, for example, as in the first exemplary embodiment, five upper parts 1 on the upper conveyor belt 8 can be assigned eleven lower parts 2 on the lower conveyor belt 9 . The upper and lower parts 1 , 2 are each fixed with their base surface on a conveyor belt 8 , 9 that their circumferential edge extends from the surface of the conveyor belt 8 , 9 away. During the circulation of the trans port belts 8 , 9 , the upper and lower parts 1 , 2 in the closing section 12 overlap and rest on one another along their peripheral edges 3 . In the subsequent deflection section 11 of the two conveyor belts 8 , 9 , the cassette parts are separated from each other again.

Each cassette is connected via a supply line section 15 to a central computer (not shown) and the necessary energy and inert gas sources. In the deflection areas 11 of the lower conveyor belt 9 is seen in the direction of rotation B in front of the closing section 12 angeord Neten feed station 13 and a behind the closing section 12 dispensing station 14 are arranged, by means of which the coming from a pick and place machine 6 of the device 7 supplied or on a subsequent work station can be delivered.

The mode of operation of the cassette system according to the invention is described below. The boards 6 from the pick-and-place machine via a conveyor line to the feed station 13 are inserted by the feed station 13 into a lower part 2 of a cassette. The cassette is closed in the closing section 12 of the device 7 , while inert gas connections are introduced into the heat treatment chamber 4 surrounding the circuit board 6 to displace the ambient air. With the closing of the cassette of the heat treatment chamber 4, via the infrared radiator 5 according to the predetermined temperature by the central computer turprogramm heated and thereby soldering the components to the board. 6 On average, a soldering time of, for example, 2 minutes is set for a circuit board 6 , so that the length of the closing section 12 , the number of cassettes and the speed of the conveyor belts 8 , 9 are to be selected accordingly. After passing through the closing section 12 , the upper part 1 is lifted from the lower part 2 and the board 6 is removed from the lower part 2 by the delivery station 14 and transferred to a transport device for transfer to the next processing station.

As shown in FIG. 1, a plurality of cassettes can be located in the closing section 12 , and, as already mentioned, different operating conditions can be set in each cassette. The work sequence described above is repeated all around for each upper and lower part ( 1 , 2 ).

Instead of a circuit board 6, a plurality of positions arranged on a carrier system can Plati NEN 6 are soldered in a cassette.

Referring to FIG. 2, the device 7 may also consist of two horizon tal arranged rotary discs 16, 17 are made. In the description of this second exemplary embodiment, the elements and functions corresponding to the first exemplary embodiment are no longer discussed. The two turntables 16 , 17 are arranged coaxially one above the other and are set in rotation by a drive motor 18 with the same circumferential speed and direction of rotation C. The two adjacent horizontal end faces of the rotary plate 16 , 17 are at a suitable distance from each other, a plurality of lifting devices 19 being provided on the end face of the upper rotary plate 17 along a pitch circle. Each lifting device 19 carries an upper part 1 , each of which is associated with an attached on the opposite end face of the lower turntable 17 lower part 2 . By means of the lifting device 19 , an upper part 1 can be lowered to close the cassette onto the corresponding lower part 2 . The feed station 13 is arranged at a circumferential distance from the lower turntable 2 , while the delivery station 14 is diametrically opposite.

The boards 6 are inserted from the feed station 13 into the lower part 2 of a cassette and the corresponding upper part 1 is placed on by means of the lifting device 19 . As in the first embodiment, the operating conditions in each cassette can be set separately via a central computer. After the closed cassette has been rotated further along the closing section 12 to the dispensing station 14 , the soldering process is ended and the upper part 2 is lifted off the lower part 2 by the lifting device 10 . The soldered board 6 is removed by the delivery station 14 from the lower part 2 and transferred to a trans port device. In this embodiment too, a plurality of cassettes can be located in the closing section 12 between the feed and discharge stations 13 , 14 , in each of which different operating conditions can be set.

The device 7 can also be constructed in the form of a paternoster system, in which the cassette revolve essentially in the vertical direction.

In the preferred embodiment described above Examples are continuously operating devices used to close the cassettes. However, it is before adjustable that discontinuous systems are used in which, for example, the top and Lower parts are stored in magazines and these with one hand device closed and to a corresponding supplier supply line can be connected.

In a modification of the device described above, it is also possible to design the cassettes in the form of a work piece 6 receiving basic cassette part 2 , which can be closed by means of a cover part guided therein. The cover part can be configured, for example, as a sliding part or similar to a roller shutter system.

Claims (13)

1. Device for heat treatment, in particular for soldering workpieces, with an essentially closed heat treatment room with a preferably inert atmosphere, characterized by at least two multi-part cassettes, the parts ( 1 , 2 ) of which are in circulation for the actual heat treatment process from one to the heat treatment room Feeding of the work piece releasing position can be brought into a closed closed position to the outside, the heat treatment chamber ( 4 ) being formed by the cassette parts ( 1 , 2 ). 2. Device according to claim 1, characterized in that the cassettes are arranged on a device ( 7 ) by means of which the cassettes can be opened all round for receiving and delivering the workpieces ( 6 ) and can be closed for the duration of the heat treatment. 3. Device according to claim 1 or 2, characterized in that the parts ( 1 , 2 ) are articulated. 4. Device according to one of claims 1 to 3, characterized in that each cassette consists of an upper part ( 1 ) and a lower part ( 2 ). 5. Device according to claim 2 and 4, characterized in that the device ( 7 ) has an upper parts ( 1 ) carry the upper turntable ( 16 ) and a lower parts ( 2 ) carrying lower turntable ( 17 ), the turntable ( 16 , 17 ) are arranged coaxially one above the other and each upper part ( 1 ) is assigned a lifting device ( 19 ) arranged on the upper turntable ( 16 ), by means of which the upper parts ( 1 ) can be placed all around onto the corresponding lower parts ( 2 ). 6. Device according to claim 2 and 4, characterized in that the device ( 7 ) from one of the upper parts ( 1 ) of the cassette-carrying circumferential upper conveyor belt ( 8 ) and one of the lower parts of the cassette-bearing, against sensible circumferential lower conveyor belt ( 9th ), the upper and lower parts ( 1 , 2 ) on the conveyor belts ( 8 , 9 ) are each at the same distance from each other and the upper parts ( 1 ) each along an adjacent parallel section ( 12 ) of both conveyor belts ( 8 , 9 ) are deductible on the corresponding lower parts ( 2 ). 7. Device according to one of claims 4 to 6, characterized in that the number of upper parts ( 1 ) is less than the number of lower parts ( 2 ). 8. Device according to one of the preceding claims, characterized by a continuous circulation of the Cassettes. 9. Device according to one of the preceding claims, characterized in that the vorbe for heat treatment agreed time-dependent temperature gradient in each cassette can be set separately.   10. Device according to one of the preceding claims, characterized in that in the closed cassettes Shielding gas can be introduced. 11. Device according to one of the preceding claims, characterized in that each workpiece ( 6 ) is assigned a cassette te. 12. Device according to one of the preceding claims, characterized in that the cassettes are essentially Chen have a rectangular base. 13. Device according to one of the preceding claims, characterized in that the cassettes are essentially Chen circular base.