Sintering presses for sintering electronic components on substrates

Abstract

A sintering press (1) for sintering electronic devices (10) on a substrate (12), comprising: at least one reaction element (40), extending between a first element end (40') and a second element end (40") along an element axis parallel to the press axis of the press (1), the first element end (40') forming a support plane for the respective substrate (12); at least one load sensor (50), operatively connected to the second element end (40") and accommodated in a sensor retaining plate (52) operatively connected to a cooling circuit (54); and an element plate (70), suitable for slidably supporting at least one reaction element (40) and equipped with a heating circuit (72). The reaction element (40) has a heating portion (40a), which passes through the element plate (70) and is suitable for transferring heat from the element plate (70) to the substrate (12) by conduction. The reaction element has a cooling portion (40b) terminating at a second end (40") and shaped to dissipate heat transferred from the element plate (70) to the heating portion (40a). The heating portion (40a) may be in the form of a prism. The cooling portion (40b) may include an axially continuous dissipation disk extending coaxially with the element axis. The second end (40") of the reaction element (40) may be equipped with an infrared screen (46) facing the load sensor (50). The sintering press (1) may include a plurality of reaction elements (40), which are slidably supported by the element plate (70), and a load sensor (50) is associated with each reaction element (40). The heating circuit (72) may be suitable for heating the element plate (70) to an operating temperature between 240°C and 290°C. The cooling circuit (54) may be suitable for maintaining the sensor retaining plate (52) at a temperature of approximately 60°C or maintaining the sensor retaining plate (52) at a temperature of approximately 25°C and maintaining the load sensor (50) at a temperature of approximately 60°C.

Description

[0001] The present invention relates to a sintering press for sintering electronic components on a substrate.

[0002] As is known, in some electronic applications, integrated electronic devices (e.g., diodes, IGBTs, thermistors, and MOSFETs) are fixed to a substrate by inserting a sintering paste. In order to properly sinter each device, it must be pressed onto the substrate when it is at the sintering temperature (e.g., greater than 200°C).

[0003] The sintering press generally comprises a base forming a pressing plane on which one or more substrates are positioned. The press is equipped with a pressing unit which, for each substrate, is equipped with one or more pressing members which are controlled, for example, by a hydraulic circuit, in order to apply a predetermined pressure to the electronic device to be sintered.

[0004] In some embodiments of the press, the base is also equipped with one or more load sensors adapted to detect the sum of the forces applied by the pressing members on the electronic devices of each substrate in order to monitor the correct operation of the press. The load sensors are electronic devices that must operate at temperatures much lower than the sintering temperature.

[0005] Therefore, one problem that plagues sintering presses of the type described above is maintaining the load cell at an operating temperature much lower than the sintering temperature, even if the load cell is operably connected to the pressing plane, since the load cell must detect the correct application of the force exerted by the pressing member on the substrate.

[0006] The object of the present invention is to propose a press capable of solving this problem.

[0007] The above object is achieved by a press according to claim 1. The dependent claims describe preferred embodiments of the invention.

[0008] The characteristics and advantages of the sintering press according to the invention will become apparent from the following description of a preferred embodiment thereof, which is provided by way of indicative and non-limiting example, with reference to the accompanying drawings, in which:

[0009] - Figure 1 is an axial cross-sectional view of a press according to the present invention; and

[0010] - Figure 2 is a perspective view of the reaction element.

[0011] In the above-mentioned drawings, a sintering press according to the present invention is generally indicated by 1.

[0012] The press is suitable for sintering the electronic device 10 on the substrate 12 .

[0013] In one embodiment, the press 1 is designed to sinter electronic devices on a plurality of substrates 12 simultaneously.

[0014] The substrate 12 holds the electronic device 10 to be sintered (e.g., IGBT, diode, thermistor, and MOSFET) placed on a layer of sintering paste. The device 10 must be processed at a predetermined surface pressure (e.g., 30 MPa) at a predetermined temperature (e.g., 260° C.) for 180 to 300 seconds.

[0015] Considering that the thickness of the device varies from family to family, the electronic device 10 must be pressed with a force proportional to its protruding surface.

[0016] The sintering press 1 comprises a frame 8 , for example extending vertically along a press axis X, which extends vertically and supports a pressing unit 14 at the top and a reaction base 60 at the bottom, and the reaction base 60 supports at least one base plate 12 , preferably a plurality of base plates 12 .

[0017] One or both of the pressing unit 14 and the base 60 can be moved relative to the other along the press axis X so that the electronic device 10 to be sintered is substantially brought into contact with the pressing unit 14 for pressing.

[0018] In one embodiment, the pressing unit 14 includes, for each substrate 12 , one or more pressing members adapted to apply a necessary sintering pressure on the electronic device 10 .

[0019] In one embodiment, the pressing unit 14 includes a multi-rod cylinder 20 equipped with parallel and independent press rods 28. Each press rod 28 is coaxial with the respective electronic device 10 to be sintered, the center of gravity of each press rod 28 is on the respective electronic device 10 to be sintered, and has a thrust section proportional to the force to be applied to the respective electronic device 10, the area of ​​each electronic device to be sintered is known. The term "center of gravity" means that each press rod 28 has a rod axis that coincides with the center of gravity of the respective electronic device 10.

[0020] In one embodiment, the pressurizing rods 28 are driven by a pressurized control fluid. For example, the pressurizing rods 28 are in communication with a compression chamber 30, into which the control fluid is introduced and into which a matching control element is housed to transmit the pressure applied by the control fluid to the pressurizing rods. For example, the control element is in the form of a membrane 32. When the compression chamber 30 is pressurized to the sintering pressure, the membrane 32 is deformed by pressing against the rear end 28' of the pressurizing rods 28 to transmit the sintering pressure to each pressurizing rod 28.

[0021] Of course, other pressurized rod actuation systems may be used.

[0022] According to one aspect of the invention, the press comprises at least one reaction element 40 extending along an element axis parallel to the press axis X between a first element end 40 ′ and a second element end 40 ″. The first element end 40 ′ forms a support plane for the respective base plate 12 .

[0023] A load sensor 50 is operatively connected to the second element end 40 ″. The load sensor 50 is adapted to detect a force exerted by one or more press rods 28 of the press unit 14 on the electronic device 10 to be sintered on the substrate 12 through the reaction element 40 .

[0024] It should be noted that the load cell 50 may be used simply to detect the pressure applied to the respective substrate, in an on / off mode of operation, or to detect the value of the pressure applied, for example by feedback pressure control, depending on specific requirements.

[0025] In one embodiment, the load sensor 50 is housed in a sensor retention plate 52 , which is operably connected to a cooling line 54 .

[0026] Each reaction element 40 is slidably supported by an element plate 70. The term "slidably supported" does not mean that the reaction element must slide in the element plate 70, but rather means that the element is inserted in a guided manner into a respective guide seat formed in the element plate without being constrained thereto. In practice, as will be described below, the element plate 70 must ensure the transfer of heat from it to the reaction element 40, keeping the reaction element 40 in the correct position parallel to the press axis X, but at the same time not affecting the forces detected by the respective load cell 50.

[0027] It should be noted that in a preferred embodiment, the second end 40" of the reaction element is always in contact with the load cell 50, whereby the reaction element 40 undergoes substantially zero or negligible axial displacement during the pressing step. In this case, the reaction element 40 provides a true contrast to the force applied by the pressing member, which contrast is then fully absorbed by the electronic device to be sintered.

[0028] In one embodiment, the element plate 70 is heated by a heating circuit 72 adapted to bring the element plate 70 and, by conduction, the reaction element 40 to a desired sintering temperature. For example, the heating circuit 72 is embedded in a heating body 74 placed around the element plate 70.

[0029] Each reaction element 40 has a heating portion 40a that passes through the element plate 70 and is adapted to transfer heat from the element plate 70 to the respective base plate 12 by conduction.

[0030] The reaction element 40 also has a cooling portion 40b which ends with a second end 40" and is shaped in such a way as to dissipate the heat transferred from the element plate 70 to the heating portion 40a.

[0031] For example, the heating portion 40a and the cooling portion 40b are continuously provided.

[0032] In one embodiment, the heating portion 40a has an axial extension substantially equal to or slightly greater than the thickness of the element plate 70. For example, the heating portion 40a terminates at a first end 40' of the reaction element 40 that protrudes axially from the element plate 70.

[0033] In one embodiment, the element plate 70 and the sensor retaining plate 52 are axially separated from each other by a separation fluid (eg, air) suitable for dissipating heat from the reaction elements.

[0034] For example, the cooling portion 40 b has an extension substantially equal to the distance between the element plate 70 and the sensor holding plate 52 .

[0035] In one embodiment, the heating portion 40a is prismatic. For example, the heating portion 40a has an axial extension that is greater than the diameter of the supporting plane of the substrate.

[0036] In one embodiment, the cooling portion 40b includes an axially continuous dissipator disk 44 that extends coaxially with the element axis.

[0037] In one embodiment, the second end 40 ″ of the reaction element 40 is equipped with an infrared screen 46 facing the load sensor 50 .

[0038] In one embodiment, the heating circuit 72 is adapted to heat the element plate to an operating temperature between 240°C and 290°C.

[0039] For example, the element plate is made of a metal material having high thermal conductivity.

[0040] For example, the heating circuit 72 comprises a resistor controlled by a resistance thermometer.

[0041] In one embodiment, the cooling circuit 54 is adapted to maintain the sensor retaining plate 52 at a temperature of approximately 25°C.

[0042] For example, the cooling system is based on the circulation of a coolant conditioned by a chiller.

[0043] Thus, the reaction element in combination with the heatable element plate and the coolable sensor retaining plate allows:

[0044] - providing heating of the sintered substrate by transferring heat conducted from the element plate to the heated portion of the reaction element;

[0045] - Counteract the sintering pressure applied by the upper pressing member;

[0046] -Transmit the reaction force to the load cell;

[0047] - Reduce heat transfer to the load cell.

[0048] Thus, the cooling circuit can maintain the load sensor at an acceptable operating temperature, such as 60° C., without excessive energy consumption.

[0049] For the embodiments of the sintering press according to the invention, those skilled in the art may make modifications, changes and substitutions of functionally equivalent elements in order to meet possible needs without departing from the scope of the appended claims. Each feature described as belonging to one possible embodiment can be implemented independently of the other described embodiments.

Claims

1. A sintering press for sintering electronic devices on a substrate, comprising: - at least one reaction element extending between a first element end and a second element end along an element axis parallel to a press axis of the press, wherein the first element end forms a support plane for a respective base plate; - at least one load sensor operatively connected to the second element end so that the load sensor detects, by means of the reaction element, the sum of the forces exerted by one or more pressing members of the press on the respective electronic device to be sintered placed on the substrate, the load sensor being housed in a sensor holding plate operatively connected to the cooling circuit; - an element plate adapted to slidably support said at least one reaction element and provided with a heating circuit, wherein: - the reaction element has a heating portion which passes through the element plate and is adapted to transfer heat from the element plate to the base plate by conduction; - The reaction element has a cooling portion terminating at the second element end and shaped to dissipate heat transferred from the element plate to the heating portion.

2. The press according to claim 1, wherein: The heating portion is in the form of a prism.

3. The press according to claim 1, wherein: The cooling portion comprises an axially continuous dissipator disk extending coaxially with the element axis.

4. The press according to claim 2, wherein: The cooling portion comprises an axially continuous dissipator disk extending coaxially with the element axis.

5. A press according to any one of claims 1 to 4, wherein: The second element end of the reaction element is provided with an infrared screen facing the load sensor.

6. A press according to any one of claims 1 to 4, wherein: The heating circuit is adapted to heat the element plate to an operating temperature between 240°C and 290°C.

7. A press according to any one of claims 1 to 4, wherein: The cooling circuit is adapted to maintain the sensor retaining plate at a temperature of 60°C.

8. A press according to any one of claims 1 to 4, comprising a plurality of reaction elements slidably supported by the element plate, the load sensor being associated with each reaction element.

Images