EP0391903A1

EP0391903A1 - Welding device

Info

Publication number: EP0391903A1
Application number: EP88907314A
Authority: EP
Inventors: Peter Gammelin
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-11-04
Filing date: 1988-09-08
Publication date: 1990-10-17
Also published as: JPH03501907A; WO1989004589A1; DE3866678D1; ATE70153T1; DE3737457A1; EP0315228A1; US5196667A; EP0315228B1

Abstract

PCT No. PCT/EP88/00812 Sec. 371 Date Jun. 27, 1990 Sec. 102(e) Date Jun. 27, 1990 PCT Filed Sep. 8, 1988 PCT Pub. No. WO89/04589 PCT Pub. Date May 8, 1989.A device for making or undoing welds between a component with several galvanic connections and a support is particularly suited for surface mounting. In order to direct a stream of hot gas or infrared radiation accurately onto the connections of the component and corresponding weld surfaces, a mask is provided which has openings that exactly match the configuration of the weld surface. Preferably, in the case of hot-air operation, a light source is arranged behind the mask in such a way that the predetermined pattern is reproduced exactly on the substrate in the form of points of light for positioning purposes. In one embodiment, the mask comprises two pairs of horizontally adjustable shields, the two pairs of shields being arranged at an angle of 90 degrees, the shields being made of a material of low thermal conductivity.

Description

Soldering device

The invention relates to a device for producing or releasing soldered connections between an electronic component provided with a plurality of galvanic connections, e.g. SMD component, and a carrier, with a heat source arranged at a distance from the soldered connection, via which a heat beam with an exchangeable beam guide is directed onto the soldered connection.

As is known, electronic assemblies consist of a rigid or flexible carrier provided with conductor tracks, on which electronic components are soldered. Both components with plug-in connecting pins for a so-called plug-in assembly are known, which are soldered in the carrier in fastening holes and in holes for through-plating, as well as components which are soldered directly onto the surface of the conductor tracks for mechanical and electrical connection. The conductor tracks do not have to be pierced or drilled through to accommodate each component. This latter technique is known as Surface Ntounted Assembly. A mixed assembly with plug-in and surface-mounted components is also common for special applications.

Special surface mount devices (SMD) are developed for surface mounting, for example resistors, capacitors, diodes, transistors, integrated circuits and chip carriers. In contrast to the components provided with pin connections, these components have connecting surfaces or short contact legs which are soldered directly to the circuit board, i.e. without connecting wires.

One of the soldering methods that can be used for SMA technology is the so-called reflow soldering, a hot gas hairdryer often being used as the heat source. The hot spot aimed at the solder - 2 -

An air jet melts the solder or a paste applied there.

Automatic assembly machines, which enable large quantities, are used to manufacture SMA assemblies in particular. However, the purchase and operating costs of these machines are so high that small quantities cannot be processed economically.

Using reflow soldering, devices are known for the production of small series, for mixed assembly, for equipping or modifying individual printed circuit boards or for exchanging individual components, in which the hot air is blown onto the component in question via nozzles. Although the beam guidance can be adapted to different component shapes by means of different, interchangeable nozzle inserts, it can happen that the entire component lies in the hot air jet due to the large scattering of the air jet and is heated as a whole. Due to the non-uniform heat absorption in the different component materials such as metal, ceramic and plastic, there is a risk that thermal stresses and hairline cracks occur which can adversely affect the functional reliability. Furthermore, in view of the variety of component shapes, it is necessary to purchase and maintain a large number of nozzle inserts. In addition, the change of use is associated with relatively long changeover times.

The invention is based on the object of specifying an invention of the type mentioned at the outset which enables the soldered connections and the component connections to be acted upon precisely without directly stressing the other components.

This object is achieved in that a mask made of temperature-resistant material with openings is provided which corresponds to the exact soldering surface positions of a component. Chen, and that there is an interchangeable holder for the mask.

A basic idea of the invention consists in dividing the heating beam into individual partial beams and directing them precisely onto the connecting surfaces, connecting legs or connecting elements, so that the heating is limited exclusively to these positions. Since the mask can be manufactured in a ratio of 1: 1 to the actual component dimensions, extremely precise beam guidance is achieved. Basically, the mask need not be limited to a single component. Of course, a configuration with several elements can also be taken into account.

The replacement of masks is carried out in a simple and time-saving manner in that several masks are arranged on a flexible strip and that there is a winding and unwinding roller for the flexible strip. The arrangement of the strip on rolls also has the advantage that a large number of different masks are accommodated in a particularly space-saving manner. As an alternative to this, it can also be expedient for a plurality of masks to be arranged on a turntable. With this measure, particularly short access times can be achieved. Copper-clad Kapton foil or thin sheet is particularly suitable as a flexible mask material. In the case of the first-mentioned material, the hole configuration can be produced particularly simply by means of photochemical processes as are known for the production of printed circuit boards. The thin sheet can be processed by punching, drilling or laser cutting.

In addition, ceramic material is also suitable, which has the advantage that it can be processed with relatively simple means. It can also be expedient to carry out the replacement of individual masks with the aid of an interchangeable frame which is brought into the desired position in a sliding guide. The assignment and selection of the individual masks to the components currently to be processed is facilitated in that each mask is provided with an identification mark and in that the device is provided with a reproduction / reading device for the mark. The individual masks can be identified both by an operator and by an electro-optical reader.

An essentially automatic mask change is made possible by the fact that a stepper motor is present which interacts with the reading device and an electronic control. A very good beam guidance is already achieved in that a hot air dryer known per se is used as the heating element. Impulse-like exposure to hot air can be achieved by using heated compressed air as the heat carrier, which also ensures a particularly precisely limited application of heat.

The heating of a gas serving as a heat carrier expediently takes place in a heating chamber with a heating element, consisting of a web with ribs arranged on both sides, in which several cylindrical heating rods are inserted. If the heating element is also to serve as a heat store, it is preferably made of metal. Instead, in view of a short response time and to save energy, it is advantageous that the heating element is made of ceramic material.

Instead of the inserted heating elements, it can also be expedient in this material that heating coils are placed or pressed onto the material. With the help of the sintering process, a diverse shape and distribution of the heating coils is possible.

A plurality of independently controllable heating wires are preferably provided to regulate the heating. The number of heated wires is varied according to the respective requirements, which can be dependent on the material or assembly In order to prevent the housing from acting as a heat storage device and to shorten the response time, it is proposed that the housing be thermally insulated. This is achieved in a particularly simple manner in that the housing is made from Kerzr .ik material. This material is also easy to machine mechanically.

The precise positioning of the espresso elements under the mask is simplified in that a light source is arranged behind the mask, so that the mask position is indicated by a light mark. In principle, it is not necessary that there are additional openings in the mask for the light marking. Rather, the light exits through the same mask openings as the heat beam. The light markings are therefore identical to the area exposed to the heat radiation. If the relevant component connections are therefore bridged to coincide with the light markings, the component is correctly positioned. Thus, work on individual parts in particular is extremely efficient, without the need for expensive processing devices.

In terms of design, it is particularly simple that the light source, a heating element provided with ribs or openings, and the mask are arranged in a line. The heating element causes light to be scattered, so that uniform, diffuse light emerges from the mask, which is particularly suitable for indicating the position.

It can also prove advantageous that the light source is arranged laterally next to the heating element. In all cases, it also proves advantageous that there is a light chamber in front of the mask in which the light is scattered. This chamber thus has the effect of a diffusing screen without the passage of the heating jet being impeded. The light can also be directed into this scattering chamber via light-conducting materials.

If an infrared heater is used as the heat source instead of a heating element over which a gas is passed, so - 6 -

Another advantage of the invention is that the positioning can be carried out with the aid of the IR rays emerging from the mask without any additional design effort.

An alternative solution and advantageous further developments are described in claim 4 and the claims which refer back to it.

The invention is described below with reference to three exemplary embodiments shown in the drawing.

1 shows a perspective view of an exploded view of a first soldering device;

FIG. 2 schematically shows a perspective view of a mask for use in the first soldering device according to FIG. 1;

Fig. 3 shows schematically a perspective vertical longitudinal section through a second soldering device;

Fig. 4 shows schematically a vertical cross section through the second soldering device;

5 schematically shows a perspective view of a heating element;

Fig. 6 shows schematically a third soldering device;

7 schematically show an example of a ^{to 9} mask.

A soldering device designated as a whole by 1 comprises, according to FIG. 1, a heat source consisting of a heating chamber 2 with heating elements 3, a fan 4, two light sources 5, a mask holder 6 and a height-adjustable stand 7 with which the soldering device device 1 is mounted such that it can be displaced in height relative to a carriage 8 which is movable in one plane. A mask 9 made of temperature-resistant material is located in the mask holder 6. A module carrier 10 with electronic components is fastened on the carriage 8 in a known manner. In order to keep the representation clear, only a single component is drawn in high magnification on the carrier. It consists of a cuboid plastic or ceramic body 12, which accommodates an electronic circuit, and of a multiplicity of metallic connecting legs 13, with which the component 11 is placed on the surface of the subrack 10. This is a basically known configuration, which is referred to as an SMD module.

Outside air or a protective gas is drawn in via the fan 4, which consists of one or more radial fans 14, and is directed past the heating elements 3 in the heating chamber. A scattering chamber 15 adjoins the heating chamber 2 in the flow direction, at the exit of which the mask holder 6 with the mask

9 is located. The hot air therefore exits only through the mask 9. The mask 9 contains the exact positions of the soldering areas between the component 11 and the subrack

10 in the form of holes, slots or an overall contour. In other words, the mask openings represent an exact image of the connection pin configuration of the component 11. Since the hot air moves essentially in a straight line and in a jet shape after it emerges from the mask 9, the individual hot air jets hit the soldering surfaces on the terminal legs 13 exactly with the correspondingly precise positioning of the soldering device 1.

The positioning is facilitated by the fact that light is directed via the light sources 5 into the scattering chamber 15 in such a way that it serves as an undirected, uniformly radiating light source. Through the openings of the mask 9, parallel light rays emerge, which are aligned exactly perpendicular to the slide 8 or to the subrack 10. The The course of the light rays 16 is identical to the emerging hot air rays.

The light beams 16 form luminous spots on the component 11 or on the subrack 10, so that the pins 8 can be positioned precisely below the mask 9 by a sideways displacement of the slide 8.

The soldering device 1 is arranged as close as possible to the component 11 by being displaced vertically via a carriage 17 guided on the stand 7.

In the following figures, the same parts as in Fig. 1 are given the same reference numerals.

FIG. 2 shows a perspective view of a strip 24 made of a heat-resistant film with several masks 9. The holes 29 of the individual masks correspond to the scale of the arrangement of connecting pins of different components. The strip 24 is held in a rigid frame 30 so that it can be inserted into a rail 31 and moved there for positioning the individual masks 9. The rail 31 is part of the mask holder 6 according to FIG. 1.

FIG. 3 shows a vertical longitudinal section of a second soldering device 1 ', which differs in constructional details from the soldering device 1 according to FIG. 1. In the example shown here, the light source 5 ^■ consists of multiple halogen lamps 43, which are disposed above the chamber Heiz¬. 2 The halogen emitters 43 are each separated from the heating chamber 2 underneath on the light exit side by a translucent diffuser 18, for example made of heat-resistant milk glass The heating elements 3 partially shade the light source 5; Due to the numerous light deflections and reflections on the heating elements 3 and the walls of the heating chamber 2, a uniform light intensity sufficient for positioning the component 11 is nevertheless achieved.

In this embodiment, the radial fans 14 are arranged laterally above the heating chamber 2 with a certain inclination. The sucked-in air reaches the heating chamber 2 via channels 19, the diffusing disks 18 also serving as a guide surface and being convex to support this function.

3 shows a conventional radial fan on the left side. On the right side, an alternative 14 'is shown in cross section, which can be used when compressed air is to be introduced into the heating chamber 2. It has a hose connection 45 for an external compressed air source (not shown). This is followed in the direction of flow by an insert 44 made of porous sintered metal for distributing compressed air.

The heating elements 3 consist of a cuboid ceramic body with a central longitudinal web 32 which runs perpendicular to the plane of the drawing. It carries a plurality of ribs 33 on both sides, which the sucked-in air flows past. In the web there are several cylindrical recesses 34, each of which has a heating element 38 consisting of a heating wire 35 which is burned into a ceramic tube. The heating rods 38 can be exchanged in a simple manner.

The mask 9 is located together with a multiplicity of other masks, the hole configuration of which is in each case with the Solder surfaces of different components are covered on a flexible film 20, for example a copper-clad Kapton film or a sheet metal film. By moving the film 20 perpendicular to the plane of the drawing, different masks can be brought into the operating position below the heating chamber 2.

In principle, a sufficiently large number of different masks can be present on such a film, and both manufacturer-specific and user-specific hole configurations can be taken into account.

As shown in FIG. 4, the film 20 is contained on a reel and an unwind spool 22. The two coils 22 can be designed in such a way that they are operated by an operator by hand, for example via knurled nuts (not shown), which are connected to the two coils 22 in a rotationally fixed manner. Alternatively, a motor-driven drive can also be present. The motor drive, which preferably comprises a stepper motor 23, is controlled by an operator via a key input 26 and a control unit 25 connected downstream. With an opto-electronic reading device 27, the sensor of which consists, for example, of a diode row, that mask 9 is determined which is in the working position below the heating chamber 2. A corresponding coding is attached to the film 20 for this purpose. In addition, non-encrypted information can be mounted on the slide, which can ^'be read by an operator at a window, is guided past which the film 20th Such a display device is particularly helpful in the case of manual adjustment of the winding / unwinding spools 22.

Deflection rollers 28 are on the housing for guiding the film 20 42 available. An alternative heating element 3 'to the heating element 3 shown in the previous figures is illustrated in FIG. 5 in a perspective view. It consists of a plurality of ceramic plates 36 arranged parallel to one another, onto each of which a heating coil 37 was baked using the thick or thin film method. The ceramic plates 36 are connected to one another via spacers 40 and combined to form a unit. The connections 39 of the individual heating coils are guided inside the spacers 40 so that they can be switched on independently of one another.

Another alternative of a soldering device 100 is shown in FIG. 6. The heat source here consists of an infrared radiator 103 with a large-area radiation outlet 102 directed downward onto a printed circuit board 110. The schematically reproduced infrared rays are designated by 116. The radiation exit 102 is optionally limited by a continuously adjustable mask 109. For this purpose, the mask 109 consists of several displaceable diaphragms 120, which are arranged in pairs. They consist of a thin, flexible and heat-resistant metallic foil material. To reduce heat dissipation, they also have poor thermal conductivity. Films with a thickness of approximately 0.1 mm have proven to be very suitable. According to arrow 107, a first pair A is guided around the radiator 103 from above to before the beam exit 102. A second pair B, of which only a diaphragm 120 is partially reproduced, is moved transversely to it according to arrow 108.

The diaphragms 120, 120 'are opened or closed in pairs in opposite directions by means of stepper motors 123 and 123' and spindle drives 122 and 122 'which are aligned transversely to one another.

Below the circuit board 110 is another infrared radiator 104, which is directed towards the underside of the board. In this way, the soldering points on the board surface are preheated to a predetermined temperature which is below a temperature critical for the components 111. The additional heat required for soldering / desoldering the components 111 is supplied in a targeted manner via the infrared radiator 103.

6 to 9 illustrate, the diaphragms 120, 120 'are arranged in pairs in such a way that they either enlarge or reduce a mask window 121, 121 "in the event of an anti-parallel movement, in that their edges 124 face or face each other This is achieved in that the drive shaft 125 of the spindle drives 122, 122 'engages in opposite threads with two orifice fastenings 126 assigned to the two orifices 120, 120. The orifices 120, 120' are in the rest are guided in horizontal rails or grooves which are arranged laterally next to the radiation outlet 102 in the direction of movement.

FIG. 7 shows a partially sectioned plan view of the soldering device 100 according to line VII-VII in FIG. 6. In order to keep the figure clear, the infrared radiator 103 is not shown in the figure, so that the edges 124 of the panel 120 are unrestricted are visible. If the horizontal diaphragm fasteners 126 are moved outwards, for example, the edges 124 move inwards and reduce the mask window 121. In order to keep the illustration clear, only a single pair of diaphragms 120 and the associated stepper motor 123 / spindle drive 122 are reproduced in FIG. 7. If in practice one only provided such a pair of diaphragms with parallel edges 124, the size of the mask window 121 could only be changed in one direction.

However, in order to be able to regulate both in the longitudinal and in the transverse direction, a further pair of orifices 120 'is arranged according to FIG. 8, the directions of movement of the two pairs of orifices 120, 120' being aligned transversely to one another. Each pair of diaphragms is actuated and adjusted independently of one another, each with its own stepper motor and spindle drive, analogously in the manner shown in FIG. 6.7.

Any desired, stepless displacement in both the X and Y directions can be used to set mask windows 121 that can be precisely specified. The mask window is always in the center of the radiation exit 102. The independent control of the panels 120, 120 'arranged in pairs allows a square or rectangular window shape to be set, so that the mask window 121 can be easily matched to the contours of the components 111 (FIG. 1) can be adjusted. It is therefore not necessary to have a fixed set of masks, which is particularly advantageous with regard to future component configurations.

8 shows three different positions I, II and III of the two diaphragms 120, 120 'which can be moved in the longitudinal and transverse directions and are arranged in pairs.

FIG. 9 illustrates an example of a continuously adjustable mask 109 ", which consists of two diaphragms 120" which can be moved antiparallel. The edges 124 of the diaphragms 120 "which determine the mask window 121" do not run parallel to one another over their entire width. Rather, they are provided symmetrically to the central axis running in the direction of movement with incisions 127 open to the front in such a way that the incisions 127 of the two relevant panels 120 "complement one another to form a rectangular mask window 121". Of course, the incision 127 can also have a different geometric shape if this is expedient for adaptation to the components to be machined. An anti-parallel movement of the two diaphragms 120 "results in a two-dimensional enlargement or reduction of the mask window 121".

If the mask 109 "consisting of two diaphragms 120" described in its basic concept in FIG. 9 is combined with a further pair of diaphragms which can be moved in the transverse direction, the shape of the mask window 121 "can be varied even further.

In computer-aided operation, it is possible to store standardized component sizes and then to actuate the individual stepper motors 123 under program control.

Claims

Claims:

1.Device for making or releasing soldered connections between an electronic component (.11) provided with a plurality of galvanic connections, e.g. an SMD component and a component carrier (10) with a heat source arranged at a distance from the soldered connection, via which a heat beam is directed onto the soldered connection and with a mask (9) for limiting the heat jet, characterized in that that several masks (9) are arranged on a movable mask carrier, so that one of the masks can optionally serve to limit the heat radiation.

2. Device according to claim 1, characterized in that the mask support is designed as a flexible strip and that a winding and unwinding roller (22) are provided for the flexible strip.

3. Device according to claim 1 or 2, characterized in that the mask carrier is designed as a turntable.

4. Device for producing or releasing soldered connections between an electronic component (11) provided with a plurality of galvanic connections, for example an SMD component and a component carrier ^ 10), with a heat source arranged at a distance from the soldered connection. Via which a heat beam is directed onto the soldered connection and with a mask {jtQ) for limiting the heat beam, characterized in that a continuously adjustable mask (109) is provided.

5. The device according to claim 4, characterized in that the continuously adjustable mask (109) consists of at least two horizontally displaceable diaphragms (120).

6. The device according to claim 5, characterized in that at least one longitudinally and transversely movable diaphragm (120) are present.

7. Device according to one of claims 5 or 6, characterized in that the diaphragms (120) are arranged in pairs in an anti-parallel manner.

8. Device according to one of the preceding claims, characterized in that the mask (9, 109) is actuated by a motor drive.

9. Device according to one of claims 1 to 8, characterized in that the mask (9, 103} consists of thin sheet metal.

10. Device according to one of the preceding claims, characterized in that the heat source consists of an infrared radiator (103).