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Title:
SINTERING PRESS FOR SINTERING ELECTRONIC COMPONENTS ON A SUBSTRATE
Document Type and Number:
WIPO Patent Application WO/2020/128832
Kind Code:
A1
Abstract:
A sintering press (1) for sintering electronic components (10) on a substrate (12), comprises a pressing unit comprising a plurality of presser rods (112) controllable to apply sintering pressure to the electronic components (10) to be sintered, a plurality of reaction elements (40) each forming a support plane for a respective substrate (12), an element plate (70) suitable to slidably support the reaction elements (40) and a heating circuit (72) comprising heating elements embedded in a heating body (76) placed around the element plate (70) to bring the element plate (70) to a sintering temperature. A heat diffusion plate (80) is placed in contact with the heating body (76) and extending onto the element plate (70) between the reaction elements (40), the heat diffusion plate (80) being made of a material (e.g., Cu) having a higher thermal conductivity than that of the element plate (70) (e.g., steel). T he heat diffusion plate (80) may comprise at least two end heat collectors (82), opposite each other and fixed, each straddling the heating body (76) and the element plate (70), and a central grid (84) that extends with contact on the element plate (70) surrounding the reaction elements (40). T he pressing unit may comprise a presser heating plate (110) slidably supporting the presser rods (112), the presser heating plate (110) comprising an inner plate (114) suitable to slidably support the presser rods (112) and a presser heating body (116) placed around the inner plate (114) and provided with heating means (118) suitable to heat the inner plate (114) and thus the presser rods (112), wherein the pressing unit may further comprise a second diffusion plate (120) placed in contact with the presser heating body (116) and extending on the inner plate (114), between the presser rods (112), the second diffusion plate (120) being made of a material (e.g., Cu) having a higher thermal conductivity than that of the inner plate (114) (e.g., steel). Compensation holes (88, 124) may be made in the heat diffusion plate (80) and/or the second diffusion plate (120) so as to guarantee uniform heating of all the reaction elements (40) and/or all the presser rods (112). The sintering press (1) may also comprise a plurality of load cells (50), each operatively connected to a reaction element (40), so that said load cell (50) detects, by means of the reaction element (40), the force exerted by one or more presser rods (112), the load cell (50) being housed in a cell holder plate (52) operatively connected to a cooling circuit (54). Each reaction element (40) may have a heating portion (40a) that passes through the element plate (70) and which is suitable to transmit by conduction the heat of the element plate (70) to the substrate (12), and a cooling portion (40b) shaped so as to dissipate the heat transmitted from the element plate (70) to the heating portion (40a). The cooling portion (40b) may comprise an axial succession of dissipating disks (44) that extend coaxially to the axis of the reaction element (40). The cooling portion (40b) may be equipped with an infrared screen (46) facing the load cell (50).

Inventors:
SCHIVALOCCHI NICOLA (IT)
Application Number:
PCT/IB2019/060922
Publication Date:
June 25, 2020
Filing Date:
December 17, 2019
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
AMX AUTOMATRIX S R L (IT)
International Classes:
H01L21/67; B30B15/06
Domestic Patent References:
WO2018122795A12018-07-05
Foreign References:
US20100032096A12010-02-11
US20100024667A12010-02-04
JP2013012541A2013-01-17
Attorney, Agent or Firm:
CHIMINI, Francesco et al. (IT)
Download PDF:
Claims:
Claims

1. A sintering press for sintering electronic components on a substrate, comprising:

a pressing unit comprising a plurality of controllable presser members for applying a sintering pressure to the electronic components to be sintered;

- a plurality of reaction elements each extending predominantly along an element axis parallel to the pressing axis of the press between a first element end and a second element end, wherein the first element end forms a support plane for a respective substrate;

- an element plate suitable to support slidably the reaction elements, the reaction elements being arranged in a matrix in said element plate and having the first end protruding from said element plate;

a heating circuit comprising heating elements embedded in a heating body placed around the element plate to bring the element plate to a sintering temperature; and

- a heat diffusion plate placed in contact with the heating body and extending onto the element plate between the reaction elements, the diffusion plate being made of a material having a higher thermal conductivity than that of the element plate.

2. A press according to claim 1, wherein the diffusion plate comprises at least two end heat collectors, opposite each other and fixed, each straddling the heating body and the element plate, and a central grid that extends with contact on the element plate surrounding the first ends of the reaction elements.

3. A press according to claim 1 or 2, wherein the pressing unit further comprises a presser heating plate slidably supporting presser members, each operable by a corresponding presser rod to act on a respective electronic component to be sintered, the presser heating plate comprising an inner plate suitable to support slidably the presser members and a presser heating body placed around the inner plate and provided with heating means suitable to heat the inner plate and thus the presser members.

4. A press according to claim 3, wherein the pressing unit comprises a second diffusion plate placed in contact with the presser heating body and extending on the inner plate, between the presser members, said second diffusion plate being made of a material having a higher thermal conductivity than that of the inner plate.

5. A press according to any one of the preceding claims, wherein the diffusion plate (s) are made of copper .

6. A press according to any one of the preceding claims, wherein the diffusion plate (s) are fixed in a removable way and with play to the respective heating bodies and to the respective plates.

7. A press according to any one of the preceding claims, wherein in the diffusion plate air flow holes are made which are shaped and/or positioned in such a way as to guarantee uniform heating of all the reaction elements and/or all the presser members.

8. A press according to any one of the preceding claims, wherein the element plate is separable from the heating body.

9. A press according to any one of the preceding claims, comprising a plurality of load cells, each operatively connected to the second element end, so that said load cell detects, by means of the reaction element, the force exerted by one or more presser members, the load cell being housed in a cell holder plate operatively connected to a cooling circuit.

10. A press according to the preceding claim, wherein each reaction element has a heating portion that passes through the element plate and which is suitable to transmit by conduction the heat of the element plate to the substrate, and a cooling portion ending with the second end and shaped so as to dissipate the heat transmitted from the element plate to the heating portion .

11. A press according to claim 10, wherein the cooling portion comprises an axial succession of dissipating disks that extend coaxially to the element axis.

12. A press according to any one of the preceding claims, wherein the second end of the reaction element is equipped with an infrared screen facing the load cell.

Description:
DESCRIPTION

" SINTERING PRESS FOR SINTERING ELECTRONIC COMPONENTS ON A

SUBSTRATE "

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

[0002] As is known, in some electronics applications, integrated electronic components, e.g. diodes, IGBTs, thermistors, MOSFETs, are fixed to a substrate by the interposition of a sintering paste. In order for each component to be sintered correctly, it must be pressed onto the substrate while it is at a sintering temperature, for example greater than 200°C.

[0003] A sintering press usually comprises a base that forms a pressing plane on which one or more substrates are positioned. The press is equipped with a pressing unit provided, for each substrate, with one or more presser members controlled for example by a hydraulic circuit to exert a predetermined pressure on the electronic components to be sintered.

[0004] In some embodiments of the press, the base is further equipped with one or more load cells suitable to detect the sum of the forces exerted by the presser members on the electronic components for each substrate in order to monitor the correct operation of the press. The load cells are electronic components that must operate at temperatures much lower than the sintering temperature .

[0005] One of the problems that afflict sintering presses of the type described above is therefore how to bring the substrates to the temperature suitable for sintering, without overheating other elements of the press that must remain at a much lower temperature, for example the load cells, and in any case without compromising the mechanical performance of the press.

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

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

[0008] The features and advantages of the sintering press according to the invention will become evident from the description hereinafter of its preferred embodiments, provided by way of indicative and non-limiting examples, with reference to the accompanying figures, wherein:

[0009] - Figure 1 is an axial section of the press according to the invention;

[0010] - Figure 2 is a plan view from the top of the element holder plate of the press, fitted with a heat diffusion plate;

[0011] - Figure 3 is a perspective view from the top of the element holder plate;

[0012] - Figure 4 shows, in perspective view, the sole heat diffusion plate associated with the element holder plate ;

[0013] - Figure 5 is a plan view from the top of the presser holder plate fitted with a heat diffusion plate; and

[0014] - Figure 6 is a perspective view from the top of the presser holder plate.

[0015] In said drawings, a sintering press according to the invention has been indicated collectively at 1.

[0016] The press is suitable for sintering electronic components 10 on a substrate 12.

[0017] In one embodiment, the press 1 is designed to perform the simultaneous sintering of electronic components on a plurality of substrates 12.

[0018] The substrates 12 hold the electronic components 10 to be sintered (e.g. IGBTs, diodes, thermistors, MOSFETs) placed on a layer of sintering paste. The components 10 must be processed with a predefined surface pressure, for example 30 MPa, at a predefined temperature, for example 260°C, for 180 to 300 seconds.

[0019] The electronic components 10 must be pressed with a force directly proportional to their projection surface, taking into account that the components are of thicknesses varied by families.

[0020] The sintering press 1 comprises a framework 8 that extends vertically and supports a pressing unit 14 at the top and a support base 60 at the bottom for at least one substrate 12, preferably a plurality of substrates.

[0021] One or both of the pressing unit and the base is movable with respect to the other along a press axis X to bring the electronic components to be sintered 10 substantially in contact with the pressing unit 14 to then carry out the pressing.

[0022] In one embodiment, the pressing unit 14 comprises, for each substrate, one or more presser members suitable to apply the necessary sintering pressure on the electronic components.

[0023] In one embodiment, the pressing unit 14 comprises a multi-rod cylinder 20 equipped with parallel and independent presser rods 28. Each presser rod 28 is coaxial and barycentric to a respective electronic component 10 to be sintered and has a thrust section proportional to the force to be exerted on the respective electronic component 10, the area of each electronic component to be sintered being known. The term

"barycentric" means that each presser rod 28 has a rod axis that coincides with the barycenter of the respective electronic component 10. [0024] In one embodiment, the presser rods 28 are driven by a pressurized control fluid. For example, the presser rods 28 communicate with a compression chamber 30 wherein the control fluid is introduced and wherein a suitable control element is housed to transfer the pressure exerted by the control fluid to the presser rods. For example, this control element is in the form of a membrane 32. When the compression chamber 30 is pressurized to the sintering pressure, the membrane 32 deforms by pressing against the rear ends 28' of the presser rods 28 for a transfer of the sintering pressure to each presser rod 28.

[0025] In one embodiment, the pressing unit further comprises a presser heating plate 110 that slidably supports the presser members 112, each of which is operable by a respective presser rod 28 to act on a respective electronic component 10 to be sintered.

[0026] In one embodiment, the presser heating plate 110 comprises an inner plate 114 suitable to support slidably the presser members 112 and a presser heating body 116 placed around the inner plate 114 and equipped with heating means 118, for example resistors, to heat the inner plate 114 and thus the presser members 112.

[0027] Naturally, other presser rod actuation systems may also be used. [0028] In accordance with one aspect of the invention, the press 1 comprises a plurality of reaction elements 40, each extending along an element axis parallel to the axis X of the press between a first element end 40' and a second element end 40". The first element end 40' forms a support plane for a respective substrate 12.

[0029] In one embodiment, a load cell 50 is operatively connected to the second element end 40". The load cell 50 is suitable to detect, by means of the reaction element 40, the force exerted by one or more presser rods 28 of the pressing unit 14 on the electronic components 10 to be sintered located on the substrate 12.

[0030] One should note that the load cell 50 may be used, according to the specific requirements, simply to detect that a pressure has been applied to the respective substrate 12, thus in ON/OFF operation mode, or to detect the value of the pressure applied, e.g. by a feedback pressure control.

[0031] In one embodiment, the load cell 50 is housed in a cell holder plate 52 operatively connected to a cooling circuit 54.

[0032] The reaction elements 40 are supported slidably by an element plate 70. The reaction elements 40 are arranged in an array in the element plate 70. The first end 40' of each reaction element 40 protrudes from the element plate 70.

[0033] The term "supported slidably" does not mean that the reaction element 40 must necessarily slide in the element plate 70, but that this element is inserted in a respective guide seat made in the element plate 70 without being bound thereto. In effect, as will be described below, the element plate 70 must ensure heat transmission therefrom to the reaction element 40, keeping the latter in the correct position parallel to the press axis X, but at the same time without affecting the force detected by the respective load cell 50.

[0034] One should note that, in a preferred embodiment, the second end 40" of the reaction element 40 is always in contact with the load cell 50 whereby, during the pressing step, the reaction element 40 undergoes a substantially null or negligible axial displacement. In this case, the reaction element 40 provides a real contrast to the force exerted by the presser member, which is then completely absorbed by the electronic components 10 to be sintered.

[0035] The element plate 70 must be heated in such a way that, by thermal conduction, the reaction elements are brought to the temperature required for sintering, for example between 240°C and 290°C.

[0036] In one embodiment, each reaction element 40 has a heating portion 40a that passes through the element plate

70 and that is suitable to transmit by conduction the heat of the element plate 70 to the respective substrate 12.

[0037] In one embodiment, the reaction element 40 has moreover a cooling portion 40b ending with the second end 40" and shaped in such a way as to dissipate the heat transmitted from the element plate 70 to the heating portion 40a.

[0038] For example, the heating portion 40a and the cooling portion 40b are consecutively arranged.

[0039] 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 ends with the first end 40' of the reaction element, which protrudes axially from the element plate 70.

[0040] For heating the element plate 70, the press comprises a heating circuit 72 comprising heating elements embedded in a heating body 76 placed around the element plate 70.

[0041] For example, the heating circuit 72 comprises electrical resistors controlled by resistance thermometers .

[0042] In accordance with one aspect of the invention, the press 1 further comprises a heat diffusion plate 80 placed in contact with the heating body 76 and extending on the element plate 70, among the reaction elements 40.

[0043] The diffusion plate 80 is made of a material with a higher thermal conductivity than that of the element plate 70.

[0044] For the element plate 70, in effect, a material is used, for example steel, which favors mechanical performance, in particular strength, rather than thermal conductivity.

[0045] For example, the diffusion plate 80 is made of copper, while the element plate 70 is made of steel.

[0046] Copper has a thermal conductivity coefficient l (W-pG 1 ·K -1 ) of 390 compared to the 60 of steel from which the element plate 70 is made.

[0047] In one embodiment, the diffusion plate 80 comprises at least two end heat collectors 82, opposite each other and fixed, each astride the heating body 76 and the element plate 70.

[0048] In one embodiment, the diffusion plate 80 further comprises a central grid 84, for example directly connected to the two end heat collectors 82, which extends with contact on the plate elements 70 surrounding the first ends 40' of the reaction elements 40.

[0049] In one embodiment, the diffusion plate 80 is fixed to the heating body 76 and the element plate 70 in a detachable manner with play, i.e. in a slidable manner, for example, by means of bolts engaging slotted holes 86 in the diffusion plate 80, in order to facilitate the different thermal expansions of the element plate and the heating body.

[0050] In one embodiment, the diffusion plate 80 also has compensation holes 88 shaped and/or positioned in such a way as to ensure uniform heating of all the reaction elements 40.

[0051] In one embodiment, the element plate 70 is separable from the heating body 76. In this way, the element plate may be replaced with another, as a function of the number and shape of the substrates to be sintered 12.

[0052] In one embodiment, the element plate 70 and the cell holder plate 52 are separated axially from each other by a separation fluid suitable to dissipate the heat of the reaction element, for example air.

[0053] For example, the cooling portion 40b has an extension substantially equal to the distance between the element plate 70 and the cell holder plate 52.

[0054] In one embodiment, the heating portion 40a is prism shaped. For example, the heating portion 40a has an axial extension greater than the diameter of the support plane of the substrate. [0055] In one embodiment, the cooling portion 40b comprises an axial succession of dissipating disks 44 that extend coaxially to the element axis.

[0056] In one embodiment, the second end 40b of the reaction element 40 is equipped with an infrared screen 46 facing the load cell 50.

[0057] In one embodiment, the cooling circuit 54 is suitable to keep the cell holder plate at a temperature of about 25°C.

[0058] For example, the cooling system is based on the circulation of a coolant conditioned by a chiller.

[0059] The reaction element 40, combined with the heatable element plate 70 and the coolable cell holder plate, therefore allows to:

[0060] - provide for the heating of the sintered substrate through the transmission of heat by conduction from the element plate to the heating portion of the reaction element;

[0061] - counteract the sintering pressure applied by the upper presser members;

[0062] - transmit the counteracting force to the load cell ;

[0063] - reduce the heat transmission to the load cell .

[0064] The cooling circuit may therefore keep the load cell at an acceptable working temperature, for example 60°C without excessive energy expenditure.

[0065] In one embodiment, a second diffusion plate 120 is placed in contact with the presser heating body 116 and extends over the inner plate 114, between the presser members 112. In other words, the second diffusion plate 120 has a plurality of openings 122 through which the upper ends of the presser members 112 protrude to be engaged by the presser rods 28.

[0066] The second diffusion plate 120 is also made of a material with a higher thermal conductivity than the inner plate 114, which for example is made of steel.

[0067] For example, also the second diffusion plate 120 is made of copper.

[0068] In one embodiment, the second diffusion plate 120 is fixed to the presser heating body 116 and to the inner plate 112 in a detachable manner with play, i.e. in a slidable manner, for example, by means of bolts engaging slotted holes of the second diffusion plate 120, in order to facilitate the different thermal expansions of the inner plate and the presser heating body.

[0069] In one embodiment, in the second diffusion plate 120 compensation holes 124 are also made, shaped and/or positioned in such a way as to ensure uniform heating of all the presser members 112. [0070] To the embodiments of the sintering press according to the invention, a person skilled in the art, to satisfy contingent needs, may make modifications, adaptations and replacements of elements with others that are functionally equivalent, without departing from the scope of the following claims. Each of the features described as belonging to a possible embodiment may be implemented independently from the other described embodiments.