Sintering press

Abstract

A sintering press for sintering electronic components (10) on a substrate (12), comprises a pressing plate (60), a heating circuit (72) adapted to bring the pressing plate (60) to a preset sintering temperature, a cooler base plate (80) extending beneath the pressing plate (60), and one or more spacer elements (4) interposed between the pressing plate (60) and the base plate (80), placed at overheating zones (62) of the pressing plate (60) and made of a thermally conductive material, so as to allow the formation of thermal bridges which lower the temperature of said overheating zones (62) when the heating circuit is activated.

Description

DESCRIPTION"SINTERING PRESS"

[0001] The present invention relates to a sintering press for sintering electronic components on a substrate . The term " substrate" does not indicate solely an electronic board, but also other types of support for electronic components , for example, in particular, heat sinks .

[0002] As is known, in certain electronic applications , integrated electronic components , for example diodes , IGBTs , thermistors , MOSFETs , are fixed to a substrate by interposing a sintering paste . For each component to be properly sintered, it must be pressed onto the substrate under appropriately controlled and balanced temperature conditions .

[0003] A sintering press usually comprises a pressing plate forming or supporting at least one pressing surface on which one or more substrates are positioned . The press is equipped with a pressing assembly provided, for each substrate, with one or more pressing members operated for example by a hydraulic circuit to exert a preset pressure on the electronic components to be sintered .

[0004] To control the temperature of the sintering process , the pressing plate is heated by a heating circuit , for example with resistors .

[0005] It has been observed, however, that in some casesthe pressing plate has a non-uniform temperature, for example due to tolerances of the heating elements of the heating circuit , or to complex geometries of the plate itself , dictated by dimensions , quantity or masses of the products to be proces sed, which increase the exchange surface with the environment , causing greater convection .

[0006] As a result of such temperature non-unif ormities of the pressing plate, the electronic components may be sintered under different and not fully controlled temperature conditions .

[0007] Since manufacturers of electronic boards require increasingly tighter tolerances in the assembly of components , there is an increasing need to control and make the temperature of the pressing plate more uniform .

[0008] The object of the present invention is to propose a press capable of meeting such a need .

[0009] Another object of the invention is to propose a press that allows to make the temperature of the pressing plate more uniform without intervening on the heating circuit , and therefore without significantly increasing the complexity and cost of the press .

[0010] These objects are achieved with a press according to claim 1 and with a method for regulating the temperature of the pressing plate according to claim 7 . The dependent claims describe preferred embodiments of the invention .

[0011] The characteristics and advantages of the sintering press according to the invention will however be evident from the description below of preferred embodiments thereof , given by way of illustration and not limitation, with reference to the accompanying figures , in which :

[0012] - Figure 1 is an axial section of an example of a sintering press according to the invention ;

[0013] - Figure 2 schematically shows the lower part of a sintering press , comprising a pressing plate and a base plate, the arrows schematically representing the heat transfer from the hotter zone to the colder zone ;

[0014] - Figure 3 is an axial section of a spacer element ; and

[0015] - Figures 4 and 4a show an example of temperature distribution of the pressing plate, before and after the positioning of spacer elements .

[0016] In said drawings , a sintering pres s according to the invention as a whole is denoted by the number 1 .

[0017] The press is suitable for carrying out the sintering of electronic components 10 on at least one substrate 12 .

[0018] In one embodiment , the press 1 is designed to carry out the simultaneous sintering of electronic components on a plurality of substrates 12 . The substrates 12 carry the electronic components 10 to be sintered ( for example IGBTs , diodes , thermistors , MOSFETs ) positioned on alayer of sintering paste . The components 10 must be processed under preset pressure and temperature conditions , for a preset time interval .

[0019] For example, the components 10 are pressed with a surface pressure of between 5 and 30 MPa, at a temperature between 240 ° C and 290 ° C, for 180 - 300 seconds .

[0020] In one embodiment , the electronic components 10 are pressed with a force directly proportional to their projected surface .

[0021] In one embodiment , the sintering press 1 comprises a supporting structure 8 , for example developing vertically along a pressing axis X .

[0022] The supporting structure 8 supports at the top a pressing assembly 14 . At the bottom, the supporting structure 8 supports a pressing plate 60 and a base plate 80 . The pressing plate 60 forms , or supports - for example slidably - at least one pressing surface 12 ' adapted to receive one or more substrates 12 .

[0023] The pressing plate 60 is thermally coupled to a heating circuit 72 , for example with electric resistors , adapted to bring and maintain the pressing plate 60 at a preset sintering temperature . Through thermal conduction, the heat is transmitted from the pressing plate 60 to the at least one pressing surface 12 ' and then to the atleast one substrate 12 .

[0024] The base plate 80 extends beneath the pressing plate 60 , is spaced from the pressing plate 60 and is maintained at a temperature lower than the sintering temperature .

[0025] For example, the pressing plate 60 and the base plate 80 are parallel to one another and extend horizontally, that is perpendicularly to the pressing axis X .

[0026] In one embodiment , the pressing plate 60 and the base plate 80 are integral with one another and may slide axially with respect to the supporting structure 8 .

[0027] For example, the base plate 80 must be maintained at a lower temperature than the sintering temperature because it supports devices , for example load cells 50 , which have an operating temperature significantly lower than the sintering temperature .

[0028] For example, the base plate 80 must be maintained at a temperature equal to or lower than about 50-60 ° C .

[0029] To this end, in one embodiment , the base plate 80 is cooled by a cooling circuit 54 .

[0030] The pressing assembly 14 and / or the assembly of the pressing plate 60 and base plate 80 is movable with respect to the other along the pressing axis X to bring the electronic components to be sintered 10 substantiallyinto contact with the pressing assembly 14 and then perform the pressing .

[0031] In one embodiment , the pressing assembly 14 comprises , for each substrate 12 , one or more pressing members 28 adapted to apply the necessary sintering pressure onto the electronic components 10 .

[0032] In one embodiment , the pressing assembly 14 is of the type described in patent publication WO2020 / 128836 and comprises a multi-rod cylinder 20 provided with pressing rods 28 that are parallel and independent of one another . Each pressing rod 28 has a pressing section proportional to the force to be exerted on the respective electronic component 10 .

[0033] In one embodiment , the pressing rods 28 are actuated by a pressurised control fluid . For example, the pressing rods 28 communicate with a compression chamber 30 into which the control fluid is introduced and in which a control element 32 is housed, adapted to transfer to the pressing rods 28 the pressure exerted by the control fluid . For example, this control element is in the form of a membrane . When the compression chamber 30 is pressurised to the sintering pressure, the membrane 32 deforms and comes into abutment against the rear ends 28 ' of the pressing rods 28 for the transfer of the sintering pressure to each pressing rod 28 .

[0034] Naturally, other systems for actuating the pressing rods may also be employed .

[0035] In accordance with an aspect of the present invention, the press 1 comprises one or more spacer elements 4 interposed between the pressing plate 60 and the base plate 80 , at overheating zones 62 of the pressing plate 60 susceptible to a heating exceeding the preset sintering temperature . The spacer elements 4 are made of a thermally conductive material so as to allow the formation of thermal bridges which lower the temperature of said overheating zones when the heating circuit 72 is activated .

[0036] Therefore, the spacer elements 4 are accessory tools capable of balancing, that is , making more uniform, the temperature distribution of the pressing plate even when the latter assumes complex geometrical configurations . With reference to figure 2 , the heat transfer from the pressing plate 60 to the base plate 80 by means of spacer elements 4 is schematically illustrated by arrows directed according to the direction of heat propagation .

[0037] In one embodiment , the spacer elements 4 are in the form of columns , or bars , for example with prismatic shape, which extend between an upper end 4a, in contact with a lower surface of the pressing plate 60 , and a lower end 4b, in contact with an upper surface of thebase plate 80 .

[0038] It should be noted that the spacer elements 4 realize a direct contact with the lower surface of the pressing plate 60 and with the upper surface of the base plate 80 , so as to maximise the effectiveness of the thermal bridge and then make the temperature of the pressing plate 60 more uniform at the overheating zones 62 .

[0039] In one embodiment , the spacer elements 4 are provided with height regulation means adapted to permit a change in the height of the spacer element s 4 .

[0040] Thanks to these height regulation means, the spacer elements 4 can be adapted to different distances between the pressing plate 60 and the base plate 80 and can also be inserted between the two plates 60 , 80 when the two plates have already been fastened to the supporting structure 8 .

[0041] Furthermore, the spacer elements 4 can be moved, once inserted between the two plates 60 , 80 , so as to be positioned exactly at the overheating zones 62 .

[0042] In one embodiment illustrated in the drawings , the spacer elements 4 are elastically yielding in the axial direction . For example, the spacer elements comprise an upper portion 7 , for example in the form of a pin, a lower portion 5 , for example a hollow portion so as toTranslation (PCT Rule 12.3) 12 August 2025 receive the lower end of the upper portion 7 , and an elastic element 6 interposed between said upper 7 and lower 5 portions . For example, the elastic element 6 is a helical spring at least partially housed in the cavity 5 ' of the hollow lower portion 5 .

[0043] The elastic element 6 makes it possible to ensure full contact between the opposite ends 4a, 4b of the spacer elements 4 and the respective plates 60 , 80 and to lock the spacer elements 4 in the chosen positions , without the risk of displacement of the spacer elements during the sintering process .

[0044] Figure 4 shows an example of a non-uniform temperature distribution of the pressing plate 60 , without the use of the spacer elements 4 . The numbers shown in figure 4 represent the temperatures , expressed in degrees Celsius , of different zones of the pressing plate 60 . In the example shown in figures 4 and 4a, the reference sintering temperature is 250 °C .

[0045] Figure 4a shows how the temperature distribution is balanced after positioning the spacer elements 4 . The numbers shown in figure 4a represent the temperatures , expressed in degrees Celsius , of different zones of the pressing plate 60 after positioning ( in this case two) spacer elements 4 , each schematically indicated in the figure with a circle .

[0046] Therefore, after heating the pressing plate 60 to a preset sintering temperature, a detection of the overheating zones 62 of the pressing plate 60 is carried out , wherein the temperature takes on a value greater than the sintering temperature .

[0047] Once said overheating zones 62 have been identified, at least one spacer element 4 is interposed between the pressing plate 60 and the base plate 80 at the overheating zones 62 .

[0048] For example, the detection of the overheating zones is carried out by means of a thermal imaging camera or with the aid of a thermocouple .

[0049] To the embodiments of the sintering press according to the invention, a person skilled in the art may apply modifications , adaptations , and substitutions of elements with others functionally equivalent , in order to meet contingent needs , without departing from the scope of the following claims . Each of the features described as belonging to a possible embodiment may be implemented independently of the other described embodiment s .

Claims

Claims1. A sintering press for sintering electronic components (10) on a substrate (12) , comprising a pressing plate (60) forming or supporting at least one pressing surface (12' ) adapted to receive one or more substrates (12) , a heating circuit (72) adapted to bring the pressing plate (60) to a preset sintering temperature, a base plate (80) extending beneath the pressing plate (60) , the base plate (80) being spaced apart from the pressing plate (60) and being kept at a lower temperature than the sintering temperature, the press being characterized in that it comprises one or more spacer elements (4) interposed between the pressing plate (60) and the base plate (80) , the one or more spacer elements (4) being placed at overheating zones (62) of the pressing plate (60) , the overheating zones being susceptible to a heating exceeding the preset sintering temperature, said spacer elements (4) being made of a thermally conductive material, so as to allow the formation of thermal bridges which lower the temperature of said overheating zones (62) when the heating circuit is activated.

2. A press according to claim 1, wherein the spacer elements (4) are in the shape of columns extending between an upper end (4a) , in contact with a lower surface of the pressing plate (60) , and a lower end (4b) ,in contact with an upper surface of the base plate (80) .

3. A press according to claim 1 or 2, wherein the spacer elements (4) are provided with height regulation means adapted to permit a change in the height of the spacer elements.

4. A press according to claim 3, wherein the spacer elements (4) are elastically yielding in an axial direction .

5. A press according to claim 4, wherein the spacer elements (4) comprise an upper portion (7) , a lower portion (5) , and an elastic element (6) interposed between said upper and lower portions .

6. A press according to any one of the preceding claims, wherein the base plate (80) is kept at a base plate temperature significantly below the sintering temperature by means of a cooling circuit (54) .

7. A method of adjusting the temperature of the pressing plate of a sintering press according to any one of the preceding claims, comprising the steps of:- heating the pressing plate (60) to a preset sintering temperature ;- detecting overheating zones (62) of the pressing plate where the temperature takes a greater value than the sintering temperature; interposing at least one spacer element (4) at theoverheating zones between the pressing plate and the base plate .

8. A method according t< > claim 7, wherein the detection of the overheating zones is carried out by means of a thermal imaging camera or by means of a thermocouple.

9. A method according to claim 7 or 8, wherein the pressing plate is heated to a sintering temperature of between 240°C and 290°C.

10. A method according t< > any one of claims 7-9, wherein the base plate is cooled 1.o a temperature of about 60 °C.

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