CH711296B1 - Continuous furnace and die bonder with a continuous furnace. - Google Patents

Abstract

The invention relates to a continuous furnace comprising a furnace body (2) and a cover (6), which enclose a channel through which substrates can be transported and to which a working gas can be supplied. The cover (6) has at least one process opening. Connecting points between individual parts of the continuous furnace, which are detachably connected to each other, are formed with opposite joining surfaces (11, 12). At least some of the connection points have a groove (15) which can be acted upon with negative pressure during operation. By the unavoidable gap between the joining surfaces (11, 12) penetrating air is sucked through the groove (15) and does not get into the furnace interior. The invention further relates to a die bonder with such a continuous furnace.

Description

description

Technical field The invention relates to a continuous furnace with a detachable cover, so that the interior of the furnace is accessible for maintenance. The furnace interior is supplied with a working gas. The invention further relates to a mounting device known as die bonder with such a continuous furnace, in which the working gas is a protective gas. Examples of "die bonders" are in particular semiconductor chips, but also capacitors, metal plates, etc.

Background of the Invention In the assembly of semiconductor chips, it is customary to connect the semiconductor chips, mainly power semiconductors, to the substrate by means of solder in order to ensure an effective dissipation of the heat loss during operation from the semiconductor chip via the solder connection. But other "die bonders" are also soldered to the substrate. The substrates used are predominantly metallic substrates, so-called leadframes.

A die bonder suitable for this process is marketed by the Applicant under the name DB 2009 SSI. This die bonder comprises a continuous furnace through which the substrates are successively conveyed to a solder station where the solder is applied and melts, to a distribution station where the solder is distributed on the substrate site, and then to a bonding station where a semiconductor chip is picked up -and-place system is placed on the liquid solder, transported. The solder can also be applied in a single process station on the respective substrate space and distributed over the substrate space. The continuous furnace is designed as a channel or tunnel with the necessary process openings. In the channel there is a protective gas atmosphere to prevent the unwanted oxidation of the substrates. Normally, hydrogen is added to the shielding gas to achieve reduction of already existing oxides. The lower the oxygen concentration in the furnace interior, the more effectively the substrate can be protected from oxidation.

The continuous furnace is formed by a furnace body and a cover which define the channel. Since the oven must be opened for maintenance, the cover is detachably connected to the furnace body. The cover is relatively heavy and therefore often placed only on the furnace body where it presses with its own weight on the furnace body. The cover can also be bolted to the furnace body. The joints between the individual parts of the cover as well as between the cover and the furnace body are formed as opposed surfaces, which are referred to as joining surfaces in the context of this disclosure. Ideally, the joining surfaces touch each other over a large area, thus ensuring that the interior of the furnace is sealed against the environment at all joints. However, since even with the most careful manufacturing unavoidable gaps between the joining surfaces remain, can penetrate through the outside air into the furnace interior, joining surfaces are basically avoided as far as possible and many other measures taken to prevent the ingress of outside air into the tunnel with flue gas channel.

In the Swiss patent application no. 01 938/13 a continuous furnace is described in which the front side wall of the channel is formed with a longitudinal slot, so that the substrates can be transported with brackets. Despite the supply of protective gas, the furnace interior of such continuous furnaces is barely under significant overpressure, since these are semi-open continuous furnaces.

There are also continuous furnaces, in which instead of a protective gas another working gas is used.

Brief Description of the Invention The invention relates to a continuous furnace of the type described above and further to a die bonder having such a continuous furnace. In a die bonder, for example, the cover of the continuous furnace has a process opening for applying solder to the substrates transported through the furnace, a process opening for distributing the solder on the substrate sites, and at least one process opening for applying the semiconductor chips to the substrates. The cover comprises at least one lid and optionally additionally at least one plate which covers one of the process openings, as well as possibly further elements. The process openings for applying and distributing the solder are covered, for example, with a plate, which is moved back and forth during operation for reasons not explained here. The plate is used to seal the corresponding process opening to prevent the ingress of oxygen as much as possible. In order to prevent the ingress of ambient air into the channel by the existing between the individual parts of the cover and the furnace body column, the connection points between the individual parts of the cover and between the parts of the cover and the furnace body are basically formed as opposed joining surfaces. The joining surfaces may or may not be planar surfaces.

Investigations by the inventors have shown that oxygen enters the channel not only at the entrance, at the exit and at the process openings and optionally through the longitudinal slot in the front side wall, but also through the very thin but unavoidable gap between the joining surfaces , To prevent this, the invention proposes to provide as many joints as possible with a groove, i. in each case form at least one of the opposing joining surfaces with a groove and to connect the groove via one or more closed channels and / or lines with a vacuum source, so that it can be acted upon in operation with negative pressure. Basically, the groove acts as a vacuum chamber and separates the interior of the furnace from the environment at the corresponding connection point. On the one hand, the negative pressure prevailing in the groove causes gases passing from the environment by diffusion and / or due to a pressure difference into the gaps between the joining surfaces, such as e.g. Oxygen only reach the groove and sucked as a result of the prevailing negative pressure and are led back to the outside. On the other hand, however, the negative pressure prevailing in the groove also causes working gas to flow from the furnace interior to the groove in the event of a pressure gradient between the interior of the furnace and the groove, where it is likewise sucked off and led out into the open. However, this loss of working gas is small and justifiable.

In the continuous furnace according to the invention thus connecting points between individual parts of the continuous furnace, which are releasably connected to each other, formed with opposite joining surfaces. At least some, preferably all, of the junctions have an oppressive groove in operation. Air which penetrates through the unavoidable gap between the joint surfaces is sucked out via the groove and does not reach the interior of the furnace.

The invention will be explained in more detail with reference to an embodiment and with reference to the drawing. The figures are shown schematically and not to scale for the sake of clarity of drawing.

Description of the Figures [0011]

1 shows in plan view parts of a continuous furnace according to the invention,

2 shows in cross section two adjacent lids of the continuous furnace,

3 shows a connection point of the continuous furnace,

4 shows a process opening of the continuous furnace covered with a plate, and FIG. 5 shows a printing scheme.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows schematically in plan view parts of a continuous furnace 1 according to the invention, which is designed in particular for use in a die bonder. The continuous furnace 1 comprises a furnace body 2, which has a bottom 3 and two side walls 4, 5, which are made in one piece or gas-tightly interconnected, and a cover 6. The furnace body 2 and the cover 6 form a channel through which substrates be transported in a direction shown by an arrow 7. This channel forms the oven interior. The front side wall 5 may include a longitudinal slot to allow the substrates to be transported through the channel with a stapling system.

The cover 6 comprises at least one cover, in this embodiment, however, a plurality of covers 8 and 9. Each of the lid 8, 9 may have one or more process openings 10. The first covers 8 are designed to be less likely to be removed, i. especially for maintenance. The second covers 9 are designed as quick-change parts, so that adjustments, e.g. Adjustments of the process openings to different processes in a short time are possible. The bottom 3 and / or one or more of the covers 8, 9 contain a plurality of holes, not shown, which are connectable to a protective gas source, so that the furnace interior during operation, a protective gas can be supplied.

The first lid 8 as well as the second lid 9 are detachably connected to the furnace body 2. In a first embodiment, the first cover 8 are only on its own weight on the furnace body 2 and are removed manually for maintenance. In a second embodiment, the first lid 8 are also with their own weight on the furnace body 2, but can also be pneumatically or hydraulically pressed against the furnace body 2 and can also, for example, for maintenance, pneumatically or hydraulically lifted from the furnace body 2. Both the first cover 8 and the second cover 9 may be bolted to the furnace body 2. The covers 8, 9 abut each other and / or overlap each other.

The process openings 10, which are there that the semiconductor chips can be placed on the transported through the channel substrates are usually permanently open. Other process openings 10, for example a process opening, through which a solder wire is guided from the outside into the channel so that solder can be melted down on the substrate, can be covered with a fixed or even an operating plate.

The joints between the covers 8, 9 and the furnace body 2 as well as the joints between adjacent lids as well as the joints between the plates and the associated lid are formed as mutually opposite joining surfaces.

In the continuous furnace so there are the following joints where there is an unavoidable gap through which oxygen can get into the furnace interior: - joining surfaces between the first lids 8 and the furnace body 2, - joining surfaces between the second lids 9 and the furnace body 2, - joining surfaces between adjacent lids 8, 9 and - joining surfaces between a lid with a process opening and the process opening covering plate.

In order to exclude or at least further reduce the penetration of ambient air through this column, preferably all of these, but at least the most important of these joints, formed with a groove and the groove via corresponding channels and / or gas lines connected to a vacuum source, the In normal operation of the continuous furnace ensures that there is a suppression in the groove. The groove is arranged in each case in one of the opposite joining surfaces of the respective connection point. Such a groove forms a vacuum chamber, which is connected in terms of gas through the inevitable gap between the joining surfaces on the one hand with the environment and on the other hand with the furnace interior.

In the following, some aspects of the invention will be explained in detail.

In order to seal the joints between the two side walls 4 and 5 by means of negative pressure, the joining surfaces 12 formed on the end faces of the side walls 4 and 5 of the furnace body 2, each with a groove 13 are provided. The grooves 13 terminate advantageously at a certain distance from the entrance and exit of the channel in order to avoid that ambient air flowing in through the inlet or outlet of the channel is sucked directly into the grooves 13. The grooves 13 may be divided by partitions 14 into individual sections. In this case, the individual sections are connected to the vacuum source. Since the joining surfaces 11 and 12 rest on one another, the grooves 13 may alternatively be arranged in the joining surfaces 11 of the cover instead of in the joining surfaces 12 of the furnace body 2.

To seal the joints between adjacent lids 8, 9 by means of negative pressure, a groove 15 in one of the opposite joining surfaces of the two covers 8, 9 is attached. In a first embodiment, the side surfaces of two adjacent lids 8 and 9 are as accurate as possible to each other and the groove 15 is formed in one of the adjacent side surfaces of the first lid 8 or the second lid 9. In a second embodiment, the first lid 8 is formed with a projection 18 overlapping the second lid 9 (FIG. 2).

The groove 15 opens either - as shown in FIG. 1 - in the groove 13 or alternatively connected via a separate gas line to the vacuum source.

Fig. 2 shows in cross section a first lid 8 and a second lid 9, which are adjacent and adjacent to each other, according to the second embodiment. For reasons of clarity of the drawing, the lid 8 is shown offset obliquely to the left above, so that the column, in the one hand outside air and on the other hand shielding gas reaches the groove 15, are clearly visible. The projection 18 is as flat as possible on the second cover 9. The groove 15 is formed either in one of the adjoining side surfaces of the adjacent covers 8, 9 (as shown) or in the underside opposite to the second cover 9 of the projection 18 of the first cover 8. The arrow 16 indicates that outside air flows into the gap between the projection 18 and the lid 9; The arrow 17 indicates that protective gas flows from the furnace interior into the gap which exists between the two adjoining side walls of the two covers 8 and 9.

Fig. 3 shows in cross-section another way to suck in the gap between two joining surfaces 11 and 12 penetrating air via a groove. This is made possible by means of a member 19 which is mounted on the outside of the continuous furnace over the gap, so that it covers the gap, and on the side facing the gap has a groove 20 which is connected to the vacuum source.

Fig. 4 shows in plan view a lid 9 having a process opening 10 which is covered with a plate 21. The plate 21 may be fixedly mounted or it may be carried by a write head (not shown). The write head is used, for example, to guide a solder wire in any direction over the substrate to write a Lotbahn on the substrate, or to distribute the deposited solder on the substrate by means of a pen acted upon by ultrasound. The plate 21 always rests on the lid 9 and slides back and forth. The underside of the plate 21 and the top of the lid 9 are formed as joining surfaces. A groove 22 surrounds the process opening 10 completely and is connected via a channel 23 to the vacuum source. The channel 23 is for example designed so that it opens at the bottom of the lid 9 in the groove 22.

The cover 6 may thus, in addition to the covers 8, 9 one or more elements 19 and one or more plates 21 have.

Since the furnace interior during operation of the continuous furnace is constantly supplied with a protective gas, the pressure in the furnace interior is equal to the atmospheric pressure or higher than the atmospheric pressure, while in the grooves 13, 15, 20 and 22 prevailing negative pressure is lower than the atmospheric pressure. The level of negative pressure in the respective grooves 13, 15, 20 and 22 is selected so that there is a slight gas flow from the furnace interior to the grooves 13, 15, 20 and 22. In order to achieve and adjust the desired negative pressure, a vacuum source 24 and a common or separate, adjustable pressure regulating valve / e 25, for example, are used as the vacuum source, to which the grooves 13, 15, 20 and 22 are connected via the gas line (s) 26. FIG. 5 shows a printing scheme for a continuous furnace comprising grooves 13 and 15.

Claims (2)

claims 1. continuous furnace, comprising a furnace body (2) and a cover (6), which surround a channel, are transportable through the substrates and a working gas can be supplied, wherein the cover (6) has at least one process opening (10), and connection points between individual parts of the continuous furnace which are detachably connected to one another, in the form of laminar connections with opposing joining surfaces (11, 12), characterized in that at least some of the connecting points have a groove (13, 15, 20, 22 ) exhibit. 2. The bonder with a continuous furnace according to claim 1.