Pressing member

Abstract

A pressing member (1) for a pressing unit of a sintering press for carrying out the sintering of electronic components onto a substrate, comprising a rigid stem and a pressing foot (12) connected to one end of the rigid stem (10). The pressing foot is made of a soft material so as to adapt to the geometric conformation of the electronic component to be pressed and protrudes axially from said end of the rigid stem both in an undeformed resting configuration and in a working deformed configuration in which it is subjected to a predetermined pressing pressure.

Description

"PRESSING MEMBER"DESCRIPTION

[0001] The present invention relates to a pressing member for pressing at least one component onto a substrate , in particular for a pressing unit of a sintering press for sintering electronic components onto a substrate .

[0002] The pressing member according to the present invention can be used in all applications in which it is necessary to exert a pressing action on an obj ect that may have a pressing surface , on which the pressing member acts , which is not orthogonal to the direction of the applied force , or a pressing surface characterised by complex geometries in which the pressing action by means of a rigid system would not be possible . One of these applications is the sintering of electronic components onto 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 correctly sintered, it must be pressed with a force proportional to its proj ection surface and subj ected to a predetermined temperature , for a certain time interval . An example of a sintering press employing pressing members according to the present invention isdescribed in WO2018122795A1 , in the name of the same Applicant .

[0004] Since di f ferent electronic components may be characterised by di f ferent thicknesses or by geometric tolerances related to their positioning, the application of pressure to them by means of one or more rigid elements may not ensure a correct distribution of pressure on each of these components . At times , even a single electronic component may have di f ferent thicknesses , making it di f ficult to ensure a correct distribution of pressure on it by means of a rigid pressing member .

[0005] In order to reduce this drawback, pressing members have been proposed provided with a pressing element made of a soft material , capable of adapting to the shape of the electronic components to be pressed .

[0006] However, pressing elements made of a soft material , although on the one hand they allow at least partly overcoming the problem of non-uni formity of the shapes and / or thicknesses of the electronic components to be sintered, on the other hand they themselves present other drawbacks . In particular, i f the material used is too soft , there is a risk that, during pressing, it expands in an uncontrolled and undesired manner, making the pressing operation not perfectly uni form over the entirepressed area and not allowing the achievement of the target pressure on the component .

[0007] In other cases , in which the pressing element is capable of insinuating itsel f between adj acent electronic components , there is a risk of inducing undesired translations of the electronic components or of causing irreversible damage to the soft material itsel f ( for example , the sharp edges of the electronic components may cause partial tearing of the soft material ) .

[0008] US 10483229B2 describes a sintering device in which a pressing cushion is housed in a seat of a pressing member, wherein said seat is laterally delimited by a fixed outer wal l and by an inner wall slidable with respect to the outer wall , such that , when the inner wall is placed in contact with the electronic components to be sintered, the pressing cushion is pressed in the direction of the lower mould .

[0009] DE102010020696B4 describes a pressing member provided with a pressing element made of a plastically deformable material , which is deformed so as to create a pressing profile complementary to the profile of the electronic components to be sintered .

[0010] DE102015120156B4 describes a sintering press provided with an elastic pressing cushion, in which said cushion is surrounded by a rigid containment structureand in which, when the containment structure is placed in contact with the substrate supporting the electronic components to be sintered, the cushion is pressed onto the components by a pressing element that translates downward with respect to the containment structure .

[0011] In all known embodiments , the pressing element made of soft material is thus in various ways confined in a lateral containment structure which, on the one hand, is made to prevent uncontrolled expansion of the soft material during pressing, but , on the other hand, results in contact between said containment structure and the electronic components to be sintered, or the substrate on which they are placed, or the press plate supporting the substrates . Such contact may cause drawbacks i f the pressure to which the pressing members are subj ected is not perfectly controlled or i f there is not perfect parallelism between the surfaces coming into contact .

[0012] Moreover, the presence of the lateral containment structure results in a spacing between the soft pressing elements of adj acent pressing members , which prevents the pressing of electronic components that are very close to each other . In other embodiments , such as in DE102010020696B4 , the presence of the lateral containment structure forces the manufacture of a pressing member with a soft pressing element having a large transversesi ze in order to press simultaneously multiple electronic components that are close to each other, which entails the need to perform the pressing action with very high values of applied force and, consequently, of the reaction force exerted by the lower plate of the press , in order to reach a predetermined pressure on the components .

[0013] The purpose of the present invention is to propose a pressing member capable of overcoming the problem of adaptation of the pressing member to possible nonuni formities in the shapes and / or thicknesses of the electronic components to be pressed, but free from the above-mentioned drawbacks with reference to the prior art .

[0014] Another purpose of the present invention is to propose a pressing member which, while being provided with a pressing element made of a deformable material , maintains a s imple structure and is therefore particularly reliable , suitable for a high number of cycles , and advantageous to produce and as semble .

[0015] A further purpose of the present invention is to propose a pressing member that allows the creation of a pressing unit capable of pressing, even simultaneously, electronic components that are very close to each other, but without increasing the value of the applied forceand, consequently, of the reaction force exerted by the lower plate of the press , necessary to reach a predetermined pressure on the components .

[0016] A still further purpose of the invention is to provide a press ing member provided with a pressing element made of soft material , which allows di f ferent pressures to be applied to di f ferent electronic components during the pressing step .

[0017] These purposes are achieved with a pressing member in accordance with claim 1 . The dependent claims describe preferred or advantageous embodiments of the pressing member according to the invention .

[0018] The features and advantages of the pressing member according to the invention will nevertheless become evident from the following description of its preferred embodiments , provided by way of example and not limitation, with reference to the accompanying figures , in which :

[0019] - Figure 1 is an axial section of an end portion of a pressing member according to the present invention, in an inactive configuration;

[0020] - Figure 2 is a view analogous to the previous one , but with the pressing member in an active pressing configuration;

[0021] - Figure 3 is a perspective view of the pressingmember, devoid of the pressing element made of deformable material .

[0022] In the continuation of the description, all directional references (for example, upper, lower, upwards, downwards, left, right, to the left, to the right, at the top, at the 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 create limitations, in particular with regard to the position, orientation or use of the described embodiments .

[0023] Conjunction references (for example, fixed, coupled, connected and the like) are to be interpreted in a broad sense and may include intermediate elements between a connection of elements and a relative movement between elements. Therefore, the conjunction references do not necessarily imply that two elements are directly connected and in a fixed relationship with each other.

[0024] Moreover, elements common to the described embodiments will be denoted by the same reference numerals .

[0025] In the accompanying drawings, the numeral 1 denotes a pressing member according to the invention as a whole.

[0026] As illustrated in Figure 2, the pressing member 1can be used, in particular but not exclusively, in a pressing unit of a sintering press for sintering electronic components 2 onto a substrate 3 . One or more electronic components 2 are placed on the substrate 3 with the interposition of a sintering paste 4 .

[0027] In a general embodiment , the pressing member 1 comprises a rigid stem 10 , which extends along a stem axis (X ) , and a pressing foot 12 connected to one end of the rigid stem 10 .

[0028] In one embodiment , the stem axis (X ) coincides with the pressing axis , that is , with the direction along which the pressing member 1 exerts the pressing action on the component or components to be pressed .

[0029] The pressing foot 12 constitutes the part of the pressing member that comes into contact with one or more obj ects to be pressed .

[0030] The pressing foot 12 is made of a soft material so as to adapt to the geometric shape of the electronic component or components to be pressed .

[0031] The pressing foot 12 protrudes axially from the end of the rigid stem 10 . In particular, the pressing foot 12 protrudes from the end of the rigid stem 10 both when the pressing foot 12 is in a resting undeformed configuration and when it is in a working de formed configuration, that is , when it is subj ected to a predetermined pressingpressure .

[0032] In other words , during the pressing action, the pressing foot 12 forms a spacer element that keeps the rigid stem 10 axially spaced from the component or components 2 to be pressed, from the substrate or substrates 3 on which the component or components are placed, and from a support plate on which the substrate or substrates are placed during the sintering of the components in the sintering press .

[0033] In other terms , the pressing foot 12 makes it possible to avoid any contact between the rigid stem 10 and the components to be sintered 2 and anything placed on the part of the press on which the components to be sintered are positioned, that is , between the rigid stem 10 and the lower mould of the press .

[0034] The pressing foot 12 is therefore the only part of the pressing member 1 that comes into contact with the components 2 to be pressed and the respective substrates 3 .

[0035] In a preferred embodiment , the hardness of the soft material of the pressing foot 12 is selected so that , in the working deformed configuration, the pressing foot 12 remains within the footprint of the end of the rigid stem ( see Figure 3 ) .

[0036] In other words , although not confined by a rigidcontainment structure , the portion of the pressing foot12 that protrudes axially from the end of the rigid stem 10 does not deform to the point of protruding radially beyond the edge of the end of the rigid stem 10 .

[0037] This allows , in particular, the creation of a pressing unit composed of several pressing members 1 as described above , capable of pressing even electronic components 2 that are very close to one another using respective pressing members 1 arranged side by side until they almost touch, that is , forming an almost null gap between them .

[0038] The possibility of pressing individual electronic components results in an optimisation of the thrust forces , and therefore of the reaction forces ( that is , the forces exerted by the lower mould of the press during the pressing step ) , which are considerably lower than those required to sinter multiple components with a single soft pressing element .

[0039] The pressing member 1 according to the invention makes it possible to press even individual electronic components 2 and therefore to apply di f ferent pressures to di f ferent electronic components during the pressing step . This possibility is precluded to the pressing members of the known art that employ a soft pressing element which, in order to press simultaneously multipleadj acent electronic components , does not allow independent pressing of di f ferent electronic components .

[0040] In one embodiment , the pressing foot 12 is partially housed in a foot seat 14 formed in the end of the rigid stem 10 .

[0041] In one embodiment , the pressing foot 12 is inserted with calibrated interference into the foot seat 14 , that is , by interference fit , or held in position by means of mechanical components separate from the rigid stem 10 .

[0042] In accordance with a further aspect of the invention, the foot seat 14 forms at least one compensation cavity 14a, 14b which remains empty when the pressing foot 12 is in the undeformed resting position and which receives a part of the pressing foot 12 when the pressing foot 12 assumes the working deformed configuration .

[0043] In other words , the foot seat 14 forms , in addition to the volume necessary to accommodate , with shape coupling, a portion of the pressing foot 12 in the inactive or resting configuration, one or more further recesses suitable for allowing a controlled partial deformation or translation of the pressing foot 12 within the foot seat 14 during the pressing action, when the pressing foot 12 is axially compressed onto the component or components 2 to be pressed .

[0044] These recesses , defined as compensation cavities14a, 14b since they perform the function of compensating for the deformation or partial translation of the pressing foot 12 , are formed in the rigid stem 10 in such a way as to avoid or at least limit deformation of the part of the press ing foot 12 that comes into contact with the component or components 2 to be pressed, so as to ensure the application of a uni form pressure on said components .

[0045] The foot seat 14 therefore performs the dual function of keeping the pressing foot 12 in position and, at the same time , ensuring its correct and partial confinement .

[0046] It should be noted that, in a preferred embodiment , at least in its end portion in which the foot seat 14 is formed, the rigid stem 12 is made in a single , monolithic body, that is , devoid of movable parts . In other words , the compensation cavities 14a, 14b are obtained by machining the end portion of the rigid stem 12 and are not obtained by means of displacements of movable parts with respect to fixed parts .

[0047] Moreover, in one embodiment , the rigid stem 10 has speci fic radii and / or chamfers suitable for avoiding possible tearing of the soft material of which the pressing foot 12 is made , which may be caused by thepresence of sharp edges on the rigid stem 10 .

[0048] In fact , as shown in Figure 2 , when the pressing member 1 is in the active press ing configuration, the soft material in contact with the component 2 to be pressed may deform by expanding radially with respect to the section of the foot seat 14 and positioning itsel f also below the end of the rigid stem 10 that surrounds the foot seat 14 . In order to prevent tearing or deterioration of the soft material , the end of the rigid stem 10 and / or the pressing foot 12 may be made with chamfers and / or radii , or with more complex geometries .

[0049] In one embodiment , the foot seat 14 defines the maximum radial footprint of the pressing foot 12 when in the undeformed resting configuration . The at least one compensation cavity 14a, 14b is formed in such a way as to prevent a radial deformation of the pressing foot 12 that would result in an increase in said maximum radial footprint .

[0050] This radial confinement of the pressing foot 12 , that is , perpendicular to the pressing axis , helps to ensure the appl ication of a uni form pressure on the component or components 2 to be pressed .

[0051] More speci fically, the foot seat 14 forms an inner side wall 144 engaged with shape coupling by at least one axial portion of the pressing foot 12 .

[0052] In one embodiment , the at least one compensation cavity 14a, 14b extends radially in such a way as not to protrude beyond the perimeter de fined by the inner side wall 144 .

[0053] one embodiment , the foot seat 14 has a bottom wall 142 forming a support surface for the pressing foot 12 when in the undeformed resting position . A first compensation cavity 14a is formed in said bottom wall 142 .

[0054] For example , said first compensation cavity 14a has a spherical cap shape with the concavity facing in the axial direction .

[0055] In one embodiment , two second compensation cavities 14b are formed in the foot seat 14 in the form of outlets extending axially from respective opposite sides of the support surface 142 .

[0056] In one embodiment , the pressing foot 12 , when in the undeformed resting position, has a prismatic shape , for example cylindrical .

[0057] In one embodiment , the pressing foot 12 , when in the undeformed resting position, has a complex geometry, suitable for improving the distribution of pressure on the pressing surface and, at the same time , reducing deterioration of the soft material . For example , the pressing foot 12 has a substantially prismatic shape , butprovided with specific radii and / or chamfers.

[0058] In one embodiment, the pressing foot 12, when in the working deformed position, expands in the axial direction thanks to the compensation cavities 14a, 14b. The compensation cavities 14a, 14b are made in such a way that the portion of the pressing foot that has expanded axially has a maximum diameter smaller than the diameter of the pressing foot 12 in the undeformed resting position .

[0059] In one embodiment, the pressing foot 12 is made of an elastomeric polymer, for example silicone-based.

[0060] In particular, in a sintering process of electronic components by means of a sintering press, the components are usually pressed with a surface pressure between 5 and 30 MPa, at a temperature between 240°C and 290°C, for 180 to 300 seconds. The material of the pressing foot 12 should meet the following requirements:

[0061] - incompressibility and elasticity;

[0062] - operating temperature up to 290°C;

[0063] - compression resistance (preferably up to 30 MPa) ;

[0064] - hardness (shore) , suitable for ensuring the correct pressure distribution.

[0065] With regard in particular to hardness, excessive hardness of the material would prevent the material from adequately conforming to the electronic component (s) orwould lead to irreversible deformation, also referred to in technical jargon as "coining", of the material itself. Conversely, a material that is not sufficiently hard could result in difficulties in reaching the target pressure on the component and could cause difficulties in keeping the non-rigid material itself in position.

[0066] An elastomeric polymer, for example silicone-based, may meet these requirements.

[0067] In other embodiments, the pressing foot 12 could be made of one or a combination of the following materials: fibrous materials, rigid materials having lamellar geometries, rigid materials processed into lattice structures (for example honeycomb) , microporous materials, multilayer laminates. Pressing feet 12 made also of these materials and / or with the above-mentioned geometries or structures, in fact, when subjected to a predetermined pressing pressure, are capable of adapting to the geometric conformation of the component to be pressed .

[0068] To the embodiments of the pressing member according to the invention, a person skilled in the art may make modifications, adaptations, and substitutions of elements with other functionally equivalent elements, in order to meet contingent requirements, without departing from the scope of the following claims. Each of thecharacteristics described as belonging to a possible embodiment may be implemented independently of the other described embodiments .

Claims

CLAIMS1. A pressing member (1) for pressing at least one component (2) onto a substrate (3) , in particular for a pressing unit of a sintering press for sintering electronic components (2) onto a substrate (3) , the pressing member comprising a rigid stem (10) extending along a stem axis (X) , and a pressing foot (12) connected to an end of the rigid stem (10) and suitable for pressing the at least one component (2) onto the substrate (3) , wherein the pressing foot (12) is made of a soft material so as to adapt to the geometric shape of the component to be pressed and protrudes axially from said end of the rigid stem in both an undeformed resting configuration and a deformed working configuration in which it is subjected to a preset pressing pressure.

2. Pressing member according to claim 1, wherein the hardness of the soft material of the foot is selected so that in the deformed working configuration, the pressing foot remains within the footprint of the end of the rigid stem.

3. Pressing member according to claim 1 or 2, wherein the pressing foot is partially housed in a foot seat (14) formed in said end of the rigid stem (10) .

4. Pressing member according to claim 3, wherein the foot seat (14) forms at least one compensation cavity (14a, 14b) which remains empty when the pressing foot (12) is in the undeformed resting position and which receives a part of thepressing foot (12) when the pressing foot (12) takes the deformed working configuration.

5. Pressing member according to claim 3 or 4, wherein the foot seat (14) has a bottom wall (142) forming a support surface for the pressing foot (12) when in the undeformed resting position, and wherein the at least one compensation cavity (14a) is formed in said bottom wall (142) .

6. Pressing member according to any one of claims 3 to 5, wherein the foot seat (14) forms an inner side wall (144) engaged with shape coupling by at least one axial portion of the pressing foot (12) .

7. Pressing member according to claims 4 and 6, wherein the at least one compensation cavity (14a, 14b) extends radially so as not to protrude beyond the perimeter defined by said inner side wall (144) .

8. Pressing member according to any one of claims 4 to 7, wherein the at least one compensation cavity (14a) is in the shape of a spherical cap with concavity facing in the axial direction.

9. Pressing member according to any one of claims 4 to 8, wherein the at least one compensation cavity comprises at least two outlets (14b) extending axially from respective opposite sides of the support surface (142) .

10. Pressing member according to any one of the preceding claims, wherein the pressing foot (12) , when in theundeformed resting position, is prismatic in shape .

11. Pressing member according to claim 10, wherein the pressing foot ( 12 ) , when in the deformed working position, has an expansion in axial direction, said expansion having a smaller maximum diameter than the diameter of the pressing foot ( 12 ) in the undeformed resting position .

12. Pressing member according to any one of the preceding claims, wherein the pressing foot ( 12 ) is made of an elastomeric polymer .

13. Pressing member according to claim 12 , wherein the pressing foot ( 12 ) is made of a silicone-based elastomeric polymer .14 . Pressing member according to any one of the preceding claims, wherein the pressing foot ( 12 ) is made of one or a combination of the following materials : fibrous materials, rigid materials having lamellar geometries, rigid materials processed into lattice structures, microporous materials, multilayer laminates .15 . Pressing member according to any one of the preceding claims , wherein the rigid stem is obtained in one piece in a single body .

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