Pressing member, in particular for sintering presses

Abstract

A pressing member, in particular for a pressing assembly of a sintering press for performing sintering of electronic components on a substrate, comprises a rigid stem (10) and an end foot (12; 112) coupled to the rigid stem by means of a ball joint (16) which allows an oscillation of the end foot with respect to the rigid stem. The ball joint consists of a ball (18) housed in a ball seat (20; 120) jointly formed by an end stem surface (22; 122) and by an apical foot surface (24; 124) facing said end stem surface.

Description

DESCRIPTION"PRESSING MEMBER, IN PARTICULAR FOR SINTERING PRESSES"

[0001] The present invention relates to a pressing member, in particular, but not exclusively, for a pressing assembly of a sintering press for sintering electronic components on a substrate .

[0002] The pressing member forming the subject-matter of the present invention can be used in all applications in which it is necessary to exert a pressing action on an object that may have a pressing surface, on which the pressing member acts , that is not orthogonal to the direction of the applied force . One of these applications is the sintering of electronic components on a substrate .

[0003] 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 . In order for each component to be properly sintered, it must be pressed with a force proportional to its projection surface and subjected to a predetermined temperature for a certain time interval . An example of a sintering press employing pressing members forming the subject-matter of the present invention is described in WO2018122795A1 , in the name of the same Applicant .

[0004] Since the layer of sintering paste on which the electronic components to be sintered are positioned may have a non-uniform thickness , it may happen that some electronic components are inclined with respect to the support , i . e . they have respective flat pressing surfaces that are not perfectly orthogonal to the direction of the force exerted by the pressing members .

[0005] In order to reduce such drawback, Italian patent 102018000007256 in the name of the same Applicant proposed a pressing member having a terminal part provided with a spherical portion so as to be able to tilt with respect to the upper portion of the pressing member itself so as to adapt to the component to be sintered .

[0006] This technical solution, however, proved to be complex to implement and in any case subject to undesirable friction forces acting in particular on the spherical portion .

[0007] The object of the present invention is to provide a pressing member of the type mentioned above, thus capable of overcoming the problem of adapting the pressing member to possible unforeseen inclinations of the flat pressing surfaces of the objects to be pressed with respect to the direction of the force exerted by the pressing members , but free from the drawbacks mentioned above with reference to the prior art .

[0008] This object is achieved by a pressing member according to claim 1 . The dependent claims describe preferred or advantageous embodiments of the pressing member according to the invention .

[0009] The features and advantages of the pressing member according to the invention will in any case become evident from the following description of preferred embodiments thereof , given by way of example and not limitation, with reference to the accompanying figures , in which :

[0010] - Figure 1 is an axial section of an end portion of a pressing member according to the present invention, in a first embodiment ;

[0011] - Figure 2 is an axial section of the pressing member of Figure 1 , according to a sectional plane orthogonal to that of Figure 1 ;

[0012] - Figure 3 is a perspective axial section of the end portion of the pressing member of Figures 1 and 2 , according to the sectional plane of Figure 1 ;

[0013] - Figure 4 is an axial section of a pressing member according to the present invention, in a second embodiment and according to the same sectional plane asFigure 1 ;

[0014] - Figure 5 is an elevation view of a pressing member according to the present invention, in an active configuration; and

[0015] - Figure 6 is an axial section of a pressing member according to the present invention, according to the same sectional plane as Figure 1 .

[0016] In the following description, all directional references ( for example, upper, lower, upward, downward, left , right , to the left , to the right , top, bottom, above, below, vertical, horizontal, clockwise and counterclockwise ) are used solely for identification purposes to assist the reader in understanding the described embodiments and do not constitute limitations , particularly with regard to the position, orientation or use of the described embodiments .

[0017] The connecting references ( for example, fixed, coupled, connected and the like ) must be interpreted broadly and may include intermediate elements between a connection of elements and relative movement between elements . Therefore, the connecting references do not necessarily imply that two elements are directly and fixedly connected to one another .

[0018] Furthermore, elements common to the described embodiments will be indicated with the same reference numerals .

[0019] In the accompanying drawings, 1; 100 denote a pressing member according to the invention as a whole. The pressing member 1; 100 can be used, in particular but not exclusively, in a pressing assembly of a sintering press for sintering electronic components on a substrate.

[0020] In a general embodiment, the pressing member 1; 100 comprises a rigid stem 10, which extends along a stem axis (X) , and an end foot 12; 112 connected to one end of the rigid stem 10.

[0021] The end foot 12; 112 thus constitutes the part of the pressing member that comes into contact with an object to be pressed.

[0022] To that end, in one embodiment, the end foot 12; 112 forms a flat terminal surface 14 suitable for coming into contact with a pressing surface of the object to be pressed (or simultaneously with several pressing surfaces of objects to be pressed) .

[0023] The end foot 12; 112 is coupled to the rigid stem 10 by means of a ball joint 16; 116 which allows an oscillation of the end foot 12; 112 with respect to the rigid stem 1 .

[0024] In accordance with one aspect of the invention, the ball joint 16; 116 consists of a ball 18 housed in a ball seat 20; 120 jointly formed by an end stem surface22; 122 and by an apical foot surface 24; 124 facing said end stem surface 22; 122.

[0025] In one embodiment, the centre of the ball 18 belongs to the stem axis (X) .

[0026] In an embodiment illustrated in Figures 1-3, the end stem surface 22 forms a concave stem surface 22a in the shape of a spherical cap complementary to the ball 18.

[0027] The apical foot surface 24 forms a concave foot surface 24a in the shape of a spherical cap complementary to the ball 18.

[0028] Therefore, at least in one use configuration (which will be described below) , in which the ball 18 is in contact both with the end stem surface 22 and with the apical foot surface 24, the ball 18 is housed with form coupling in the ball seat 20.

[0029] In a variant embodiment illustrated in Figure 4, the apical foot surface 124 forms a concave foot surface 124a having a radius of curvature greater than the radius of the ball 18.

[0030] In this case, the ball 18 ideally has a single point of tangency with the concave foot surface 124a.

[0031] For example, the concave foot surface 124a is a parabolic surface.

[0032] In the embodiment of Figures 1-3, the pressure exerted by the ball 18 on the end foot 12 is distributedover a surface ( for example equal to or slightly smaller than a hemispherical surface ) , whereas in the embodiment of Figure 4 , the pressure exerted by the ball 18 on the end foot 112 is substantially concentrated at one point . Compared to the embodiment of Figures 1-3 , the point contact between the ball 18 and the end foot 112 allows minimization of the friction forces between the ball 18 and the concave foot surface 124a, to the benefit of the freedom of oscillation of the end foot 112 . However, the high pressure exerted by the ball on said concave foot surface 124a may result in coining or other alterations of the sliding surface of the ball .

[0033] In both illustrated embodiments , the end stem surface 22 ; 122 and the apical foot surface 24 ; 124 are axially spaced from one another so as to allow a certain degree of inclination of the end foot 12 ; 112 with respect to the rigid stem 10 .

[0034] Furthermore, in one embodiment , the apical foot surface 24 ; 124 comprises an annular peripheral portion 24b; 124b of f rustoconical shape converging into the concave foot surface 24a; 124a .

[0035] In one embodiment , the end stem surface 22 ; 122 comprises an annular peripheral portion 22b; 122b of f rustoconical shape surrounding the concave stem surface22a; 122a and tapering in the direction facing the end foot 12 ; 112 .

[0036] It is noted that the tapered shape, in particular f rustoconical, of the annular peripheral portion of the apical foot surface 24b; 124b and of the annular peripheral portion of the end stem surface 22b; 122b allows reduction of the contact surface between the ball 18 and the stem / foot in order to limit friction, and also to avoid possible mechanical interference between such surfaces when the pressing member is in the active configuration .

[0037] In one embodiment , at least one release recess 28a, 28b is obtained in the ball seat 20 ; 120 , which reduces the contact surface between the ball 18 and the ball seat 20 ; 120 .

[0038] For example, at least one release recess 28a, 28b is obtained around the stem axis (X) in the end stem surface and / or in the apical foot surface .

[0039] In a preferred embodiment , thanks to the fact that the ball 18 is a component separate from the rigid stem 10 and from the end foot 12 ; 112 , it is possible to make the rigid stem 10 and the end foot 12 ; 112 in a first material and the ball 18 in a second material different from the first material .

[0040] In particular, the second material may be selected so as to have a low friction coefficient , forexample lower than the friction coefficient of the first material .

[0041] In one embodiment, the pressing member 1; 100 further comprises axial connection means 30 suitable for axially constraining, with clearance, the end foot 12; 112 to the rigid stem 10.

[0042] Furthermore, the pressing member 1; 100 is provided with elastic alignment means 32 acting axially between the rigid stem 10 and the end foot 12; 112.

[0043] By virtue of the presence of these elastic alignment means 32, the end foot 12; 112 is movable, with respect to the rigid stem 10, between an advanced resting position and an active retracted position. The end foot 12; 112 is normally urged into the advanced resting position by the elastic alignment means 32.

[0044] In this advanced resting position, the end foot 12; 112 is engaged by the axial connection means 30, which act as a mechanical stop in the direction of axial advancement. Furthermore, the elastic alignment means 32 operate in such a way as to cause the end foot 12; 112 to assume a position coaxial with the stem axis (X) . In this advanced resting position, for example, the flat terminal surface 14 is perpendicular to the stem axis (X) .

[0045] When the pressing member 1; 100 comes into contact with an object to be pressed, the latter exerts areaction force which, overcoming the force of the elastic alignment means 32, causes the end foot 12; 112 to shift from the advanced resting position to the active retracted position .

[0046] In this active retracted position, the end foot 12; 112 is disengaged from the axial connection means and is engaged by the ball 18.

[0047] In other words, when in the active retracted position, the end foot 12; 112 is connected to the rigid stem 10 through the ball 18, which in this case also acts as an axial stop for the end foot 12; 112. Therefore, in this configuration, the ball 18 abuts against the concave terminal surface 22a of the rigid stem 10 and the concave apical surface 24a is in contact with the ball 18.

[0048] This configuration is defined as "active" in that the end foot 12; 112, adapting through the ball 18 to the inclination of the object to be pressed, can exert the desired pressure on the object.

[0049] As can be seen from the figures, when it is in the active retracted position, the end foot 12; 112 is slightly detached from the axial connection means 30, in the axial and / or transverse direction, so as to have the necessary clearance to tilt.

[0050] Figure 5 shows the pressing member 1; 100 in the active pressing position of a chip to be sintered 200 ona substrate 202 . The layer of sintering paste 204 , and consequently the chip to be sintered 200 placed thereon, are shown as exaggeratedly inclined with respect to a plane orthogonal to the stem axis (X) . In this case, the foot 12 ; 112 tilts with respect to the rigid stem 10 , so as to adapt to the inclination of the chip 200 .

[0051] In one embodiment , the axial connection means 30 comprise at least one pair of opposite lateral coupling arms 34 extending axially from the end of the rigid stem 10 towards the end foot 12 ; 112 and each forming a respective radial tooth 34 ' facing the stem axis (X) . For example, each coupling arm 34 has an "L" shape, with the radial tooth 34 ' perpendicular to the stem axis (X) .

[0052] In other words , each radial tooth 34 ' forms an abutment plane 34" facing the end stem surface 22 .

[0053] The connection means 30 further comprise at least one pair of radial recesses 36 opposite to one another and obtained in the end foot 12 ; 112 . Each radial recess 36 is axially engaged, with clearance, by a respective radial tooth 34 ' . The expression "with clearance" indicates that the radial recess 36 has an axial extension slightly greater than the axial thickness of the radial tooth 34 ' , so as to allow the end foot 12 ; 112 to perform the stroke between the advanced resting position and the active retracted position .

[0054] Each radial recess 36 forms an undercut in the end foot 12 ; 112 . Each radial recess 36 therefore forms a top portion of the foot 38 which, when the end foot 12 ; 112 is in the advanced resting position, is engaged by the abutment plane 34" .

[0055] In order to allow the axial displacement of the end foot 12 ; 112 between the advanced position and the retracted position, the top portion of the foot 38 is also housed with clearance between the abutment plane 34" and the end stem surface 22 .

[0056] Furthermore, in one embodiment shown in particular in Figures 3 and 4 , each coupling arm 34 has a tapered shape in its terminal axial portion 34a, which engages the radial recess 36, so as to facilitate the oscillation of the foot 12 ; 112 with respect to the lateral coupling arms 34 , and thus with respect to the rigid stem 10 .

[0057] In one embodiment , the elastic alignment means 32 comprise at least one pair of helical springs 40 which extend parallel to the stem axis (X) into respective spring seats 42 obtained partly in the rigid stem 10 and partly in the end foot 12 ; 112 .

[0058] In order to return and maintain the end foot 12 ; 112 , in the advanced resting position, coaxially with the stem axis (X) , the helical springs 40 are positionedsymmetrically with respect to the stem axis (X) . For example, as in the embodiment illustrated in the drawings , the main axes of the helical springs 40 lie on a spring plane perpendicular to a coupling arm plane on which the main axes of the lateral coupling arms 34 lie .

[0059] In one embodiment shown in Figure 6, the distance between the apical foot surface 24 ; 124 and the flat end surface 14 is less than or equal to twenty times the radius of the ball 18 .

[0060] In other words , in this embodiment , the following relationship holds :

[0062] h being the distance between the apical foot surface 24 ; 124 and the flat end surface 14 , and r the radius of the ball 18 .

[0063] It is evident that the pressing member described above allows the intended object to be achieved .

[0064] It is worth noting that the pressing member according to the present invention allows , compared to articulated pressing members of the known art, to reduce as much as possible the distance between the centre of rotation of the end foot and the component to be pressed . This makes it pos sible, for an equal inclination angle of the end foot with respect to the stem axis (X) , to limitundesirable horizontal displacements of the end foot and therefore of the component itself during the pressing action with the end foot inclined .

[0065] To the embodiments of the pressing member according to the invention, a person skilled in the art , in order to meet contingent needs , may make modifications , adaptations and replacements of elements with functionally equivalent ones , 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 pressing member, in particular for a pressing assembly of a sintering press for sintering electronic components on a substrate, comprising a rigid stem (10) extending along a stem axis (X) , and an end foot (12; 112) connected to one end of the rigid stem (10) , the end foot (12; 112) being coupled to the rigid stem (10) by means of a ball joint (16) which allows the end foot to oscillate with respect to the rigid stem, characterized in that the ball joint consists of a ball (18) accommodated in a ball seat (20; 120) jointly formed by an end stem surface (22; 122) and an apical foot surface (24; 124) facing said end stem surface.

2. Pressing member according to claim 1, wherein the centre of the ball belongs to the stem axis (X) .

3. Pressing member according to claim 1 or 2, wherein the end stem surface (22; 122) forms a concave stem surface (22a; 122a) in the shape of a spherical cap complementary to the ball (18) .

4. Pressing member according to any one of the preceding claims, wherein the apical foot surface (24) forms a concave foot surface (24a) in the shape of a spherical cap complementary to the ball.

5. Pressing member according to any one of claims 1-3, wherein the apical foot surface (124) forms a concave foot surface (124a) having a radius of curvature greater thanthe radius of the ball (18) .

6. Pressing member according to claim 4 or 5, wherein said apical foot surface (24, 124) comprises an annular peripheral portion (24b; 124b) of f rustoconical shape converging into the concave foot surface (24a; 124a) .

7. Pressing member according to any one of the preceding claims, wherein at least one release recess (28a, 28b) is obtained in the ball seat, which reduces the contact surface between the ball (18) and the ball seat (20; 120) .

8. Pressing member according to claim 7, wherein at least one release recess (28a, 28b) is obtained about the stem axis (X) in the end stem surface and / or in the apical foot surface .

9. Pressing member according to any one of the preceding claims, wherein the rigid stem (10) and the end foot (12; 112) are made of a first material and the ball (18) is made of a second material different from the first material .

10. Pressing member according to claim 9, wherein the second material has a lower friction coefficient than the friction coefficient of the first material.

11. Pressing member according to any one of the preceding claims, further comprising:- axial connection means (30) suitable for axially constraining and with clearance the end foot (12; 112) to the rigid stem (10) ;- elastic alignment means (32) acting axially between the rigid stem and the end foot so that the end foot is movable between an advanced resting position, in which it is axially urged by said elastic alignment means (32) so as to be engaged by the axial connection means (30) to take a position coaxial to the stem axis (X) , and an active retracted position, in which it is disengaged from the axial connection means (30) and engaged by the ball (18) .

12. Pressing member according to claim 11, wherein said axial connection means (30) comprise:- a pair of lateral coupling arms (34) opposite to each other extending axially from the end of the rigid stem towards the end foot and each forming a respective radial tooth (34' ) facing the stem axis (X) ;- a pair of radial recesses (36) obtained in the end foot, each radial recess (36) being axially engaged, with clearance, by a respective radial tooth (34' ) .

13. Pressing member according to any one of claims 11-12, wherein said elastic alignment means comprise at least one pair of helical springs (40) opposite to each other with respect to the stem axis (X) and extending parallel to the stem axis (X) into respective spring seats (42) obtained partly in the rigid stem and partly in the end foot.

14. Pressing member according to any one of the preceding claims, wherein the end foot forms, on the opposite side with respect to the rigid stem, a flat end surface (14)suitable for abutting against an object to be pressed.

15. Pressing member according to any one of the preceding claims, wherein the distance between the apical foot surface (24; 124) and the flat end surface (14) is less than or equal to twenty times the radius of the ball (18) .

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