A welding pad group, welding substrate, thermistor and welding pad steel mesh

Abstract

The present invention provides a pad group, a welding substrate, a thermistor and a pad steel mesh, wherein the pad group includes a first pad and a second pad with a groove gap therebetween, the groove gap includes a first arcuate surface convex to the first pad and a second arcuate surface convex to the second pad symmetrically distributed about a symmetry axis; the two pads respectively overlap with the projections of the two arcuate surfaces on the pad group to form a first arcuate edge and a second arcuate edge. The present invention avoids the increase of thermal resistance due to excessive thickness of solder paste and collapse or poor solder beads of excessively thick solder paste through the arcuate surface of the groove gap between the pad groups; at the same time, the arcuate surface of the groove gap limits the glass body of the thermistor in the center of the groove gap to avoid positional displacement when the thermistor is mounted; in addition, the size and position of the arcuate surface of the pad group are set to adapt to the cumulative position tolerance of the thermistor welded by the pad group, thereby reducing the risk of poor welding of the thermistor; finally, the pad steel mesh matched with the pad group reduces the contact area between the glass body and the solder paste.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor integrated circuit manufacturing, and in particular relates to a pad group, a welding substrate, a thermistor and a pad steel mesh. Background Art

[0002] In the application technology of IGBT (Insulate-Gate Bipolar Transistor) modules, one of the most critical parameters is the temperature of the IGBT chip. Therefore, NTC (Negative Temperature Coefficient) thermistors are often welded inside the IGBT power module to detect the module temperature. In the actual production process, the electrodes at both ends of the NTC thermistor are welded to two copper foil pads a few millimeters apart to support the thermistor glass body in the middle. At present, the pads used to weld NTC thermistors in IGBT power modules are mostly as follows: Figure 1-Figure 2 The straight pad shown in the figure cannot effectively limit the welding position of the NTC thermistor, which makes the NTC thermistor easily shift in position during the welding process; in addition, because the spacing between the pads cannot be too large, the electrode at one end of the NTC thermistor will tilt up when the tin is creeping, resulting in a "tombstone phenomenon", which will cause cold soldering or poor welding problems. The position shift and tombstone phenomenon of the NTC thermistor are difficult to repair, which will directly lead to product scrapping, thereby increasing manufacturing costs. At the same time, the cold soldering problem in the NTC thermistor is difficult to detect, which will seriously affect the reliability of the product.

[0003] In the prior art, the commonly used NTC thermistor glass body is a prism, and the electrode is a cylinder. The surface of the prism is used to limit the rotation, thereby solving the problem of positional deviation of the NTC thermistor during welding to a certain extent. However, due to the distance difference between the side edge of the prism glass body and the side of the cylinder of the electrode, it is required that the plane of the glass body must be parallel to the solder paste surface on the pad during patching; if the side edge of the glass body is facing the solder paste surface during patching, the solder paste thickness must be greater than about 0.2 mm to ensure that the solder paste thickness reaches the distance difference between the side edge of the glass body and the side of the cylinder, so that the electrode is in contact with the solder paste surface.

[0004] However, in actual application, NTC thermistors are packaged using common SMT (Surface Mount Technology) tapes, which cannot fix the direction of the patch, resulting in the inability to ensure that the glass surface of the NTC thermistor is parallel to the solder paste surface during patching. The industry's commonly used printed solder paste thickness is 0.15mm±30%. When the printed thickness of the solder paste is increased to 0.2mm to ensure that the electrode can also contact the solder paste when the side edge faces the solder paste, the BLT (Bond Line Thickness) of the chip on the same substrate as the NTC thermistor increases, the thermal resistance rises, the heat dissipation is large, and the product reliability is reduced. In addition, the increase in solder paste thickness itself will cause the solder paste to collapse during printing, or produce solder beads during welding, causing the solder beads to sputter to locations without pads, affecting the reliability of subsequent wire bonding processes.

[0005] Therefore, there is an urgent need for a structure or method that can improve the position accuracy and welding reliability of thermistor patches.

[0006] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because these solutions are described in the background technology part of the present application. Summary of the invention

[0007] In view of the above shortcomings of the prior art, the object of the present invention is to provide a pad group, a welding substrate, a thermistor and a pad steel mesh, which are used to solve the problems of poor position accuracy and low reliability of thermistor patches in the prior art.

[0008] To achieve the above object, the present invention provides a pad group, the pad group comprising a first pad and a second pad symmetrically arranged about a symmetry axis, a groove gap is arranged between the first pad and the second pad, and the inner surface of the groove gap is an insulating material; the first pad and the second pad are respectively used to weld a first electrode and a second electrode of a thermistor, and the first electrode and the second electrode are connected through a glass body of the thermistor;

[0009] A side of the groove gap close to the first pad is a first arcuate surface convex toward the first pad, and a side of the groove gap close to the second pad is a second arcuate surface convex toward the second pad, and the first arcuate surface and the second arcuate surface are symmetrically distributed about the symmetry axis;

[0010] The projections of the first solder pad and the first curved surface on the solder pad group coincide with each other to form a first curved edge convex toward the first solder pad, and the projections of the second solder pad and the second curved surface on the solder pad group coincide with each other to form a second curved edge convex toward the second solder pad; the direction perpendicular to the axis of symmetry and parallel to the solder pad group is the first direction, and the direction parallel to the axis of symmetry and parallel to the solder pad group is the second direction, the maximum distance between the first curved edge and the second curved edge along the first direction is the first preset distance, and the maximum chord lengths of the first curved edge and the second curved edge along the second direction are both the second preset distances.

[0011] Optionally, the first preset distance is L1, the cumulative position tolerance of the pad group welding the thermistor along the first direction is x, the length of the glass body along the first direction is a1, and L1=a1-x.

[0012] Optionally, the second preset distance is L2, the cumulative position tolerance of the thermistor welded by the pad group along the second direction is y, the length of the glass body along the second direction is a2, and L2=a2+y.

[0013] The present invention also provides a welding substrate, which includes any one of the above-mentioned pad groups, the bottom surface of the groove gap between the pad groups is lower than the upper surface of the welding substrate at both ends of the groove gap, and the pad groups are located on the upper surface of the welding substrate at both ends of the groove gap.

[0014] Optionally, the welding substrate is a direct copper-clad ceramic substrate.

[0015] Optionally, the welding substrate includes an IGBT power module having a thermistor.

[0016] The present invention also provides a thermistor, which is used for welding on any one of the above-mentioned welding pad groups or any one of the above-mentioned welding pad groups on the welding substrate; the thermistor includes a glass body, a first electrode and a second electrode; the glass body includes a right quadrangular prism, the right quadrangular prism includes a third bottom surface and a fourth bottom surface and a prism side surface formed by four side edge surfaces connected in sequence through side edges; the first electrode and the second electrode are both cylinders, the cylinder of the first electrode includes a first bottom surface and a cylindrical side surface, and the cylinder of the second electrode includes a second bottom surface and a cylindrical side surface;

[0017] The first bottom surface of the first electrode is fixedly connected to the third bottom surface of the glass body, the second bottom surface of the second electrode is fixedly connected to the fourth bottom surface of the glass body, and the diameters of the first bottom surface and the second bottom surface are both equal to the side lengths of the third bottom surface and the fourth bottom surface; the portion where the third bottom surface of the glass body is connected to the side edge of the prism side surface is a first curved surface convexly away from the center of the glass body, and the portion where the fourth bottom surface of the glass body is connected to the side edge of the prism side surface is a second curved surface convexly away from the center of the glass body;

[0018] The first arc surface is consistent with the first arc surface of the groove gap of any one of the above-mentioned pad groups, and the second arc surface is consistent with the second arc surface of the groove gap of any one of the above-mentioned pad groups, so that when the thermistor is welded on the pad group and the side edge surface of the prism side surface of the glass body closest to the groove gap is not parallel to the upper surface of the pad group, the distance between the cylindrical side surface of the first electrode and the first pad in the pad group is less than or equal to the preset third distance, and the distance between the cylindrical side surface of the second electrode and the second pad in the pad group is less than or equal to the preset third distance.

[0019] Optionally, the preset third distance is less than or equal to 0.15 mm.

[0020] The present invention also provides a pad steel mesh, which is used to set solder paste on any one of the above-mentioned pad groups or any one of the above-mentioned pad groups on the welding substrate; the pad steel mesh includes at least a first pad opening and a second pad opening, the first pad opening corresponds to a preset position for setting solder paste on the first pad of the pad group, and the second pad opening corresponds to a preset position for setting solder paste on the second pad of the pad group; the side of the first pad opening close to the first arcuate edge is a third arcuate edge parallel to the first arcuate edge, and the side of the second pad opening close to the second arcuate edge is a fourth arcuate edge parallel to the second arcuate edge.

[0021] Optionally, when the solder paste is set on the welding substrate, the minimum distance between the third arcuate edge of the first solder pad opening and the first arcuate edge is greater than or equal to 0.15 mm, and the minimum distance between the fourth arcuate edge of the second solder pad opening and the second arcuate edge is greater than or equal to 0.15 mm.

[0022] As described above, the pad group, welding substrate, thermistor and pad steel mesh of the present invention have the following beneficial effects:

[0023] The present invention sets a first arc surface and a second arc surface in the groove gap between the pad groups, so that when the side edge of the glass body of the thermistor faces downward, the first arc surface and the second arc surface can be matched along the first arc surface and the second arc surface to be embedded in the groove gap, so that the thickness of the solder paste does not need to be too thick, and the first electrode and the second electrode of the thermistor can contact the solder paste on the first pad and the second pad, so as to avoid the increase of thermal resistance caused by the excessive thickness of the solder paste, reduce the heat dissipation capacity of the product, and avoid the collapse of the excessively thick solder paste or the sputtering of solder beads to cause poor subsequent wire bonding process, and avoid the edge of the groove gap from scratching the edge of the glass body of the thermistor;

[0024] The present invention can limit the glass body of the thermistor in the center of the groove gap by setting the first arc surface and the second arc surface of the groove gap, thereby avoiding the position deviation of the thermistor during the patch process, reducing the problem of cold soldering or poor soldering deviation, and reducing the patch process precision requirement of the thermistor.

[0025] The present invention sets the size and position of the first arc surface and the second arc surface of the pad group to adapt to the cumulative position tolerance of the thermistor welded by the pad group, thereby further reducing the risk of poor welding of the thermistor.

[0026] The present invention provides a solder pad steel mesh matched with the solder pad group, reduces the contact area between the glass body and the solder paste, and reduces the problem of defective solder beads generated during the welding process. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The diagram is a top view schematic diagram of a thermistor being welded to a pad group in the prior art.

[0028] Figure 2 A schematic top view of a pad group for soldering a thermistor in the prior art is shown.

[0029] Figure 3 Shown is a schematic structural diagram of the pad group in the present invention.

[0030] Figure 4 It is a schematic diagram of a three-dimensional view of the thermistor glass body in the prior art when the side edge surface is parallel to the solder paste patch.

[0031] Figure 5 It is a schematic top view of the thermistor glass body in the prior art when the side edge surface is parallel to the solder paste patch.

[0032] Figure 6 It is a schematic diagram of a front view of the thermistor glass body in the prior art when the side edge surface is parallel to the solder paste patch.

[0033] Figure 7 It is a schematic side view of the thermistor in the prior art when the side edge of the glass body is parallel to the solder paste patch.

[0034] Figure 8 It is a schematic three-dimensional diagram of the thermistor glass body side edge facing the solder paste patch in the prior art.

[0035] Fig. 9 It is a schematic diagram of a top view of the thermistor glass body in the prior art when the side edge faces the solder paste patch.

[0036] Fig.10 It is a schematic diagram of a front view of the thermistor in the prior art when the side edge of the glass body faces the solder paste patch.

[0037] Fig.11 It is a schematic side view of the thermistor in the prior art when the side edge of the glass body faces the solder paste patch.

[0038] Fig.12 It is a schematic three-dimensional diagram of a patch on a pad group with the side edge of the thermistor glass body facing the groove gap in the present invention.

[0039] Fig.13 It is a schematic top view of the thermistor glass body side edge facing the groove gap patch on the pad group in the present invention.

[0040] Fig.14 It is a schematic diagram of a front view of a patch on a pad group with the side edge of the thermistor glass body facing the groove gap in the present invention.

[0041] Fig.15 It is a schematic side view of the thermistor glass body side edge facing the groove gap patch on the pad group in the present invention.

[0042] Fig.16 Shown is a schematic structural diagram of the welding substrate in the present invention.

[0043] Fig.17 Shown is a three-dimensional structural schematic diagram of the thermistor in the present invention.

[0044] Fig.18 Shown is a schematic diagram of the top view structure of the thermistor in the present invention.

[0045] Fig.19 Shown is a front view structural schematic diagram of the thermistor in the present invention.

[0046] Fig. 20 Shown is a side view structural schematic diagram of the thermistor in the present invention.

[0047] Fig.21 It is a schematic three-dimensional diagram showing the case where the side edge of the thermistor glass body closest to the groove gap is parallel to the solder paste patch in the present invention.

[0048] Fig. 22It is a schematic top view of the thermistor glass body of the present invention when the side edge surface closest to the groove gap is parallel to the solder paste patch.

[0049] Fig.23 It is a schematic diagram of a front view when the side edge surface of the thermistor glass body closest to the groove gap is parallel to the solder paste patch in the present invention.

[0050] Fig.24 It is a schematic side view diagram showing the case where the side edge surface of the thermistor glass body closest to the groove gap is parallel to the solder paste patch in the present invention.

[0051] Fig.25 Shown is a schematic diagram of the structure of the pad steel mesh on the welding substrate in the present invention.

[0052] Fig.26 It is a schematic diagram of the structure after solder paste is set on the welding substrate in the present invention.

[0053] Component number description

[0054] 10. Welding substrate; 11. First linear pad; 12. Second linear pad; 13. Groove gap;

[0055] 20. pad group; 21. first pad; 22. second pad; 23. first arcuate edge; 24. second arcuate edge; 25. first preset distance; 26. second preset distance; 27. first arcuate surface; 28. second arcuate surface;

[0056] 30. thermistor; 31. glass body; 311. third bottom surface; 312. fourth bottom surface; 313. side edge surface; 314. side edge; 32. first electrode; 321. first bottom surface; 33. second electrode; 331. second bottom surface; 332. side surface of cylinder; 34. solder paste; 341. solder paste surface; 35. first arc surface; 36. second arc surface;

[0057] 41. First pad opening; 42. Second pad opening; 43. Third arc-shaped edge; 44. Fourth arc-shaped edge. DETAILED DESCRIPTION

[0058] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0059] For example, when describing the embodiments of the present invention in detail, for the sake of convenience, the schematic diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0060] For convenience of description, spatially relative terms such as "under", "below", "below", "below", "above", "on", etc. may be used herein to describe the relationship of one element or feature shown in the drawings to other elements or features. It will be understood that these spatially relative terms are intended to encompass other orientations of the device in use or operation in addition to the orientation depicted in the drawings.

[0061] In the context of the present application, a structure in which a first feature is described as being "above" a second feature may include embodiments in which the first and second features are in direct contact, and may also include embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0062] It should be noted that the illustrations provided in the present invention are only used to illustrate the basic concept of the present invention in a schematic manner, and therefore the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0063] It should be noted that the bottom parts of the first electrode 32 and the second electrode 33 of the thermistor 30 in the drawings provided in the present invention are embedded in the solder paste 34. This is because the solder paste itself is a material that is easily deformed under stress. When the thermistor 30 is soldered to the solder paste surface 341 during the process, the first electrode 32 and the second electrode 33 will exert a certain stress on the solder paste 34, so that the first electrode 32 and the second electrode 33 form a solder connection with the solder paste 34 on the pad group 20.

[0064] The present invention provides a pad group 20, such as Figure 3 As shown, the pad group 20 includes a first pad 21 and a second pad 22 symmetrically arranged about a symmetry axis, a groove gap 13 is arranged between the first pad 21 and the second pad 22, and the inner surface of the groove gap 13 is an insulating material; the first pad 21 and the second pad 22 are respectively used to weld a first electrode 32 and a second electrode 33 of a thermistor 30, and the first electrode 32 and the second electrode 33 are connected through a glass body 31 of the thermistor 30;

[0065] A side of the groove gap 13 close to the first pad 21 is a first arcuate surface 27 convex toward the first pad 21, and a side of the groove gap 13 close to the second pad 22 is a second arcuate surface 28 convex toward the second pad 22, and the first arcuate surface 27 and the second arcuate surface 28 are symmetrically distributed about the symmetry axis;

[0066] The projections of the first solder pad 21 and the first curved surface 27 on the solder pad group 20 coincide with each other to form a first curved edge 23 convex toward the first solder pad 21, and the projections of the second solder pad 22 and the second curved surface 28 on the solder pad group 20 coincide with each other to form a second curved edge 24 convex toward the second solder pad 22; the direction perpendicular to the axis of symmetry and parallel to the solder pad group 20 is the first direction, and the direction parallel to the axis of symmetry and parallel to the solder pad group 20 is the second direction, the maximum distance between the first curved edge 23 and the second curved edge 24 along the first direction is the first preset distance 25, and the maximum chord lengths of the first curved edge 23 and the second curved edge 24 along the second direction are both the second preset distance 26.

[0067] In the prior art, such as Figure 1-Figure 2 As shown, Figure 1 FIG. 1 is a top view of the thermistor 30 being welded to the pad group 20. Figure 2 FIG. 2 is a top view of the pad group 20. The first electrode 32 and the second electrode 33 at both ends of the glass body 31 of the NTC thermistor 30 are respectively welded to two copper foil pads separated by several millimeters to support the glass body 31 of the thermistor 30 in the middle. Currently, the pads used to weld the NTC thermistor 30 in the IGBT power module are mostly as follows: Figure 1 The first linear pad 11 and the second linear pad 12 shown in the figure cannot effectively limit the welding position of the NTC thermistor 30, which causes the NTC thermistor 30 to easily shift position during the welding process, or cause problems such as cold welding or poor welding, which seriously affects the reliability of the product. The commonly used NTC thermistor 30 currently sets the glass body 31 as a prism and the electrode as a cylinder, and uses the surface of the prism to limit the position deviation and rotation of the thermistor 30 to a certain extent. However, due to the distance difference between the side edge 314 of the prism glass body 31 and the side of the cylindrical electrode, as shown in FIG. Figure 4-Figure 7 As shown, Figure 4 It is a three-dimensional diagram of the thermistor 30 side edge surface 313 being parallel to the solder paste 34 in the prior art. Figure 5 It is a top view of the thermistor 30 side edge surface 313 parallel to the solder paste 34 patch in the prior art. Figure 6 It is a side view of the thermistor 30 in the prior art when the side edge surface 313 is parallel to the solder paste 34 patch. Figure 7This is a front view of the thermistor 30 side edge surface 313 parallel to the solder paste 34 when the chip is mounted in the prior art, requiring that the plane of the glass body 31 must be parallel to the solder paste surface 341 on the pad when the chip is mounted; Figure 8-Figure 11 As shown, Figure 8 It is a three-dimensional diagram of the thermistor 30 in the prior art when the side edge 314 faces the solder paste 34 for patching. Fig. 9 It is a top view of the thermistor 30 when the side edge 314 is facing the solder paste 34 in the prior art. Fig.10 It is a side view of the thermistor 30 in the prior art when the side edge 314 faces the solder paste 34. Fig.11 This is a front view of the thermistor 30 in the prior art when the side edge 314 faces the solder paste 34. It is required that the plane of the glass body 31 must be parallel to the solder paste surface 341 on the pad when the patch is mounted. If the side edge 314 of the glass body 31 faces the solder paste surface 341 when the patch is mounted, the thickness of the solder paste 34 must be greater than about 0.2 mm, otherwise it cannot be guaranteed that the first electrode 32 and the second electrode 33 are in contact with the solder paste surface 341. However, in actual application, the NTC thermistor 30 is packaged using a common material tape of SMT (Surface Mount Technology), such as Figure 10-11 As shown in the figure, the glass surface of the NTC thermistor 30 cannot be parallel to the solder paste surface 341 during mounting; and when the thickness of the solder paste 34 is increased to 0.2 mm to ensure that the side edge 314 of the glass body 31 faces the solder paste surface 341 and the electrode can contact the solder paste 34, the BLT (Bond Line Thickness) of the chip on the same substrate as the NTC thermistor 30 will increase, the thermal resistance will increase, the heat dissipation will be large, and the product reliability will be reduced; and the increase in the thickness of the solder paste 34 itself will also cause the solder paste 34 to collapse during printing, or generate solder beads during welding, causing the solder beads to splash to a position without a pad, affecting the reliability of the subsequent wire bonding process.

[0068] The present invention provides a first arc surface 27 and a second arc surface 28 of the groove gap 13 between the pad groups 20, such as Figure 12-Figure 15 As shown (only half of the pad substrate and the pad group 20 below the thermistor 30 are shown, leaving the other half of the thermistor 30 suspended in the air to clearly show the positional relationship between the thermistor 30 and the pad group 20), wherein Fig.12 This is a three-dimensional diagram of the thermistor 30 glass body 31 side edge 314 facing the groove gap 13 and being mounted on the pad group 20 in the present invention. Fig.13 This is a top view of the thermistor 30 glass body 31 side edge 314 facing the groove gap 13 on the pad group 20 in the present invention. Fig.14 This is a side view of the thermistor 30 glass body 31 with the side edge 314 facing the groove gap 13 and mounted on the pad group 20 in the present invention. Fig.15The front view of the patch on the pad group 20 with the side edge 314 of the glass body 31 of the thermistor 30 facing the groove gap 13 in the present invention is such that when the side edge 314 of the glass body 31 of the thermistor 30 faces downward, the first curved surface 35 and the second curved surface 36 can be matched and embedded in the groove gap 13 along the first curved surface 27 and the second curved surface 28, so that the thickness of the solder paste 34 does not need to be too thick to make the first electrode 32 and the second electrode 33 of the thermistor 30 contact with the solder paste 34 on the first pad 21 and the second pad 22, so as to avoid the increase of thermal resistance caused by the excessive thickness of the solder paste 34 and reduce the heat dissipation capacity of the product; and since the contact between the electrode and the solder paste 34 is achieved without the need for an excessively thick solder paste 34, it can be avoided that the excessively thick solder paste 34 collapses or sputters out solder beads, causing poor subsequent wire bonding process; at the same time, the first curved surface 27 and the second curved surface 28 of the groove gap 13 and the thermistor 3 The first curved surface 35 and the second curved surface 36 of the glass body 31 of the thermistor 30 are matched, so that the edge of the groove gap 13 can avoid scratching the edge of the glass body 31 of the thermistor 30, reduce the damage to the glass body 31 of the thermistor 30 when the thermistor 30 is mounted, and ensure the normal working performance of the thermistor 30; in addition, by setting the first curved surface 27 and the second curved surface 28 of the groove gap 13, the glass body 31 of the thermistor 30 can be limited in the center of the groove gap 13, thereby avoiding the position deviation of the thermistor 30 during the mounting process, reducing the problem of cold soldering or poor welding deviation, and reducing the mounting process accuracy requirement of the thermistor 30. Even if the thermistor 30 is not accurately mounted to the correct position during the mounting process, the first curved surface 27 and the second curved surface 28 can limit the glass body 31 so that the thermistor 30 is finally mounted at the correct position.

[0069] In one embodiment, the first preset distance 25 is L1, the cumulative position tolerance of the pad group 20 welding the thermistor 30 along the first direction is x, the length of the glass body 31 along the first direction is a1, and L1=a1-x.

[0070] In one embodiment, the second preset distance 26 is L2, the cumulative position tolerance of the pad group 20 welding the thermistor 30 along the second direction is y, the length of the glass body 31 along the second direction is a2, and L2=a2+y.

[0071] The present invention sets the size and position of the first curved surface 27 and the second curved surface 28 of the pad group 20 so that the first curved surface 27 and the second curved surface 28 can adapt to the cumulative position tolerance of the thermistor 30 welded to the pad group 20 in two-dimensional directions. Therefore, when a dimensional deviation within a certain tolerance range of the cumulative position tolerance occurs, it can still be ensured that the structures of the first curved surface 27 and the second curved surface 28 actually obtained can still meet the contact between the electrode and the solder paste 34 and the limiting effect on the glass body 31, further reducing the risks of welding offset, poor solder joints, etc. of the thermistor 30.

[0072] Specifically, in actual applications, the cumulative position tolerance of the thermistor 30 soldered to the pad group 20 is generally expressed by the sum of the mounting process tolerance of the thermistor 30, the printing process tolerance of the solder paste 34 on the pad group 20, and the tolerance of the fixture clamping the soldering substrate 10 when printing the solder paste 34, which are three tolerances with main influencing factors; among them, the printing process tolerance of the solder paste 34 on the pad group 20 is the tolerance between each pad opening and the corresponding pad edge in the soldering substrate 10, which is also the most important tolerance; other possible tolerances such as materials and dimensions are small and can be ignored.

[0073] In one embodiment, the tolerance of the fixture for holding the welding substrate 10 is 0.1 mm.

[0074] In one embodiment, the printing process tolerance of the solder paste 34 disposed on the pad group 20 is 0.15 mm.

[0075] The present invention also provides a welding substrate 10, such as Fig.16 As shown, the welding substrate 10 includes any one of the above-mentioned pad groups 20, the bottom surface of the groove gap 13 between the pad groups 20 is lower than the upper surface of the welding substrate 10 at both ends of the groove gap 13, and the pad group 20 is located on the upper surface of the welding substrate 10 at both ends of the groove gap 13.

[0076] In one embodiment, the welding substrate 10 is a direct copper-bonded ceramic substrate.

[0077] Specifically, the present embodiment mainly adopts a direct copper-clad ceramic substrate as the welding substrate 10. Since the direct copper-clad ceramic substrate is smaller in size, the solution of the present invention can better reflect the role of solving the poor welding problems such as the "tombstone phenomenon" caused by the small spacing between the first pad 21 and the second pad 22. However, the solution of the present invention is also applicable to various other suitable welding substrates 10 to improve the welding position accuracy and welding quality of the thermistor 30.

[0078] In one embodiment, the soldering substrate 10 includes an IGBT power module having a thermistor 30 .

[0079] Specifically, since the IGBT power module has a large demand for the thermistor 30 and high performance requirements for the thermistor 30, the improvement of the welding quality and welding accuracy of the thermistor 30 by the solution of the present invention can be better reflected in the welding substrate 10 of the IGBT power module including the thermistor 30, but the solution of the present invention can also be applied to other welding substrates 10 including various suitable circuit modules.

[0080] The present invention also provides a thermistor 30, such as Figure 17-Figure 20 As shown, Fig.17 is a three-dimensional diagram of the thermistor 30 in the present invention, Fig.18 is a top view of the thermistor 30 in the present invention, Fig.19 is a front view of the thermistor 30 in the present invention, Fig. 20 : is a side view of a thermistor 30 in the present invention, wherein the thermistor 30 is used to be welded on any one of the above-mentioned pad groups 20 or the above-mentioned pad groups 20 on the welding substrate 10; the thermistor 30 includes a glass body 31, a first electrode 32 and a second electrode 33; the glass body 31 includes a right quadrangular prism, and the right quadrangular prism includes a third bottom surface 311 and a fourth bottom surface 312 and a prism side surface formed by four side edge surfaces 313 connected in sequence through side edges 314; the first electrode 32 and the second electrode 33 are both cylinders, and the cylinder of the first electrode 32 includes a first bottom surface 321 and a cylindrical side surface 332, and the cylinder of the second electrode 33 includes a second bottom surface 331 and a cylindrical side surface 332;

[0081] The first bottom surface 321 of the first electrode 32 is fixedly connected to the third bottom surface 311 of the glass body 31, and the second bottom surface 331 of the second electrode 33 is fixedly connected to the fourth bottom surface 312 of the glass body 31. The diameters of the first bottom surface 321 and the second bottom surface 331 are both equal to the side lengths of the third bottom surface 311 and the fourth bottom surface 312. The portion where the third bottom surface 311 of the glass body 31 is connected to the side edge 314 of the prism side is a first curved surface 35 convexly away from the center of the glass body 31, and the portion where the fourth bottom surface 312 of the glass body 31 is connected to the side edge 314 of the prism side is a second curved surface 36 convexly away from the center of the glass body 31.

[0082] The first arc surface 35 matches the first arc surface 27 of the groove gap 13 of any of the above-mentioned pad groups 20, and the second arc surface 36 matches the second arc surface 28 of the groove gap 13 of any of the above-mentioned pad groups 20, so that when the thermistor 30 is welded on the pad group 20 and the side edge surface 313 of the prism side surface of the glass body 31 closest to the groove gap 13 is not parallel to the upper surface of the pad group 20, the distance between the cylindrical side surface 332 of the first electrode 32 and the first pad 21 in the pad group 20 is less than or equal to the preset third distance, and the distance between the cylindrical side surface 332 of the second electrode 33 and the second pad 22 in the pad group 20 is less than or equal to the preset third distance.

[0083] Since there is a height difference between the glass body 31 and the first electrode 32 and the second electrode 33 in the structure of the thermistor 30, and the thermistor 30 includes the first curved surface 35 and the second curved surface 36, when the thermistor 30 is packaged with the SMT tape, it is impossible to ensure that the first electrode 32 and the second electrode 33 of the thermistor 30 can contact the solder paste 34 to form a reliable welding when the thermistor 30 is mounted; and the arrangement of the pad group 20 in the present invention, such as Figure 8-Figure 11 As shown, when the side edge 314 of the glass body 31 of the thermistor 30 faces the groove gap 13, it can be matched with the structure of the thermistor 30, such as Figure 21-24 As shown (only half of the pad substrate and the pad group 20 below the thermistor 30 are shown, leaving the other half of the thermistor 30 suspended in the air to clearly show the positional relationship between the thermistor 30 and the pad group 20), wherein Fig.21 This is a three-dimensional diagram of the thermistor 30 glass body 31 of the present invention when the side edge surface 313 closest to the groove gap 13 is parallel to the solder paste 34 patch. Fig. 22 This is a top view of the thermistor 30 glass body 31 of the present invention when the side edge surface 313 closest to the groove gap 13 is parallel to the solder paste 34 patch. Fig.23 This is a front view of the thermistor 30 glass body 31 of the present invention when the side edge surface 313 closest to the groove gap 13 is parallel to the solder paste 34 patch, Fig.24 This is a side view of the thermistor 30 glass body 31 of the present invention when the side edge surface 313 closest to the groove gap 13 is parallel to the solder paste 34 for patching. When the side edge surface 313 of the glass body 31 of the thermistor 30 closest to the groove gap 13 is parallel to the solder paste surface 341, the welding position of the thermistor 30 can also be limited, thereby ensuring the welding accuracy and welding quality of the thermistor 30 during patching, avoiding welding defects such as cold soldering and welding offset, and avoiding the risk of damage to the thermistor 30 caused by scratching the edge of the groove gap 13 during the patching process. Therefore, the structure of the thermistor 30 is suitable for the pad group 20 provided in the present invention, and can achieve a good welding matching effect.

[0084] In one embodiment, the preset third distance is less than or equal to 0.15 mm.

[0085] Since the thickness of the printed solder paste 34 is commonly used in the industry to be 0.15 mm ± 30%, when the printed thickness of the solder paste 34 increases significantly, the BLT (Bond Line Thickness) of the chip on the same substrate as the NTC thermistor 30 will increase significantly, the thermal resistance will increase, the heat dissipation will be large, and the reliability of the product will be significantly affected. Therefore, setting the preset third distance can ensure that the thickness requirement of the solder paste 34 can be met when the thermistor 30 is embedded in the groove gap 13.

[0086] Preferably, the preset third distance is less than or equal to 0.105 mm.

[0087] The present invention sets the preset third distance to be less than or equal to the minimum thickness of the solder paste 34 within the tolerance range in the industry, thereby ensuring that the thickness requirement of the solder paste 34 is met when the thermistor 30 is embedded in the groove gap 13 .

[0088] The present invention also provides a pad steel mesh, such as Fig.25 As shown, the pad steel mesh is used to set solder paste 34 on any one of the pad groups 20 described above or the pad group 20 on any one of the welding substrates 10 described above; the pad steel mesh includes at least a first pad opening 41 and a second pad opening 42, the first pad opening 41 corresponds to a preset position for setting solder paste 34 on the first pad 21 of the pad group 20, and the second pad opening 42 corresponds to a preset position for setting solder paste 34 on the second pad 22 of the pad group 20; the side of the first pad opening 41 close to the first arcuate edge 23 is a third arcuate edge 43 parallel to the first arcuate edge 23, and the side of the second pad opening 42 close to the second arcuate edge 24 is a fourth arcuate edge 44 parallel to the second arcuate edge 24.

[0089] The present invention provides a third arcuate edge 43 and a fourth arcuate edge 44 of the pad steel mesh that match the first arcuate edge 23 and the second arcuate edge 24 of the pad group 20, such as Fig.26 As shown, it can be ensured that the third arcuate edge 43 of the printed solder paste 34 matches the first arcuate edge 23 of the first pad 21, and the fourth arcuate edge 44 of the solder paste 34 matches the second arcuate edge 24 of the second pad 22, so that the printing area of ​​the solder paste 34 on the first pad 21 and the second pad 22 is maximized, and the reliability of the welding of the thermistor 30 is ensured. At the same time, it is avoided that the solder paste 34 falls into the groove gap 13 due to the shape difference between the first pad opening 41 or the second pad opening 42 and the edge of the groove gap 13, and the undesirable problem of short circuit between the first electrode 32 and the second electrode 33 after welding is avoided, thereby improving the welding quality of the thermistor 30.

[0090] In one embodiment, Fig.25 As shown, when the solder paste 34 is set on the welding substrate 10, the minimum distance between the third arcuate edge 43 of the first solder pad opening 41 and the first arcuate edge 23 is greater than or equal to 0.15 mm, and the minimum distance between the fourth arcuate edge 44 of the second solder pad opening 42 and the second arcuate edge 24 is greater than or equal to 0.15 mm.

[0091] The present invention sets the distance between the first arc edge 23 and the second arc edge 24 of the pad group 20 and the third arc edge 43 and the fourth arc edge 44 of the matching pad steel mesh to prevent the solder paste 34 from falling into the area where the glass body 31 is located due to factors such as process tolerance, thereby reducing the contact area between the glass body 31 and the solder paste 34, thereby reducing the problem of defective solder beads generated during the welding process and improving the welding reliability of the thermistor 30.

[0092] Specifically, the pad substrate and pad group 20 shown in the present invention only show the structure near the thermistor 30. Those skilled in the art can design the corresponding pad substrate and the arrangement of the pad substrate, pad group 20 and other circuit components other than the thermistor 30 according to needs.

[0093] In summary, the pad group, welding substrate, thermistor and pad steel mesh of the present invention can be provided with the first arc surface and the second arc surface of the groove gap between the pad groups, so that when the side edge of the glass body of the thermistor faces downward, the first arc surface and the second arc surface can be matched along the first arc surface and the second arc surface to be embedded in the groove gap, so that the thickness of the solder paste does not need to be too thick, and the first electrode and the second electrode of the thermistor can be in contact with the solder paste on the first pad and the second pad, so as to avoid the increase of thermal resistance caused by the excessive thickness of the solder paste and reduce the heat dissipation capacity of the product, and to avoid the collapse of the excessively thick solder paste or the sputtering of solder beads to cause poor subsequent wire bonding process, and to avoid the edge of the groove gap from contacting the thermistor Scratches on the edge of the glass body; at the same time, by setting the first curved surface and the second curved surface of the groove gap, the glass body of the thermistor can be limited to the center of the groove gap, thereby avoiding positional deviation of the thermistor during the patch process, reducing the problem of cold soldering or poor soldering deviation, and reducing the patch process accuracy requirements of the thermistor; in addition, by setting the size and position of the first curved surface and the second curved surface of the pad group, the cumulative position tolerance of the thermistor welded by the pad group is adapted to further reduce the risk of poor soldering of the thermistor; finally, a pad steel mesh matching the pad group is set to reduce the contact area between the glass body and the solder paste, and reduce the problem of poor solder beads generated during welding.

[0094] Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0095] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A pad group, characterized in that: The pad group includes a first pad and a second pad symmetrically arranged about a symmetry axis, a groove gap is arranged between the first pad and the second pad, and the inner surface of the groove gap is an insulating material; the first pad and the second pad are respectively used to weld a first electrode and a second electrode of a thermistor, and the first electrode and the second electrode are connected through a glass body of the thermistor; A side of the groove gap close to the first pad is a first arcuate surface convex to the first pad, and a side of the groove gap close to the second pad is a second arcuate surface convex to the second pad, and the first arcuate surface and the second arcuate surface are symmetrically distributed about the symmetry axis; the first arcuate surface and the second arcuate surface of the groove gap between the pad groups enable the first arcuate surface and the second arcuate surface of the thermistor to be matched and embedded in the groove gap along the first arcuate surface and the second arcuate surface when the side edges of the glass body of the thermistor are welded to the pad group with the side edges facing downward; The projection of the first pad and the first arcuate surface on the pad group overlaps to form a first arcuate edge convex to the first pad, and the projection of the second pad and the second arcuate surface on the pad group overlaps to form a second arcuate edge convex to the second pad; The direction perpendicular to the axis of symmetry and parallel to the pad group is the first direction, the direction parallel to the axis of symmetry and parallel to the pad group is the second direction, the maximum distance between the first arc edge and the second arc edge along the first direction is the first preset distance, and the maximum chord lengths of the first arc edge and the second arc edge along the second direction are both the second preset distances.

2. The pad group according to claim 1, characterized in that: The first preset distance is L1, the cumulative position tolerance of the pad group welding the thermistor along the first direction is x, the length of the glass body along the first direction is a1, and L1=a1-x.

3. The pad group according to claim 1, characterized in that: The second preset distance is L2, the cumulative position tolerance of the pad group welding the thermistor along the second direction is y, the length of the glass body along the second direction is a2, and L2=a2+y.

4. A welding substrate, characterized in that: The welding substrate includes the pad group described in any one of claims 1-3, the bottom surface of the groove gap between the pad groups is lower than the upper surface of the welding substrate at both ends of the groove gap, and the pad group is located on the upper surface of the welding substrate at both ends of the groove gap.

5. The welding substrate according to claim 4, characterized in that: The welding substrate is a direct copper-clad ceramic substrate.

6. The welding substrate according to claim 4, characterized in that: The welding substrate includes an IGBT power module with a thermistor.

7. A thermistor, characterized in that: The thermistor is used for welding on the pad group described in any one of claims 1 to 3 or the pad group on the welding substrate described in any one of claims 4 to 6; the thermistor includes a glass body, a first electrode and a second electrode; the glass body includes a right quadrangular prism, the right quadrangular prism includes a third bottom surface and a fourth bottom surface and a prism side surface formed by four side edge surfaces connected in sequence through side edges; the first electrode and the second electrode are both cylinders, the cylinder of the first electrode includes a first bottom surface and a cylindrical side surface, and the cylinder of the second electrode includes a second bottom surface and a cylindrical side surface; The first bottom surface of the first electrode is fixedly connected to the third bottom surface of the glass body, the second bottom surface of the second electrode is fixedly connected to the fourth bottom surface of the glass body, and the diameters of the first bottom surface and the second bottom surface are both equal to the side lengths of the third bottom surface and the fourth bottom surface; the portion where the third bottom surface of the glass body is connected to the side edge of the prism side surface is a first curved surface convexly away from the center of the glass body, and the portion where the fourth bottom surface of the glass body is connected to the side edge of the prism side surface is a second curved surface convexly away from the center of the glass body; The first arc surface is consistent with the first arc surface of the groove gap of the pad group described in any one of claims 1 to 3, and the second arc surface is consistent with the second arc surface of the groove gap of the pad group described in any one of claims 1 to 3, so that when the thermistor is welded on the pad group and the side edge surface of the prism side surface of the glass body closest to the groove gap is not parallel to the upper surface of the pad group, the distance between the cylindrical side surface of the first electrode and the first pad in the pad group is less than or equal to the preset third distance, and the distance between the cylindrical side surface of the second electrode and the second pad in the pad group is less than or equal to the preset third distance.

8. The thermistor according to claim 7, characterized in that: The preset third distance is less than or equal to 0.15 mm.

9. A pad steel mesh, characterized in that: The pad steel mesh is used to set solder paste on the pad group described in any one of claims 1-3 or the pad group on the welding substrate described in any one of claims 4-6; the pad steel mesh includes at least a first pad opening and a second pad opening, the first pad opening corresponds to a preset position for setting solder paste on the first pad of the pad group, and the second pad opening corresponds to a preset position for setting solder paste on the second pad of the pad group; the side of the first pad opening close to the first arcuate edge is a third arcuate edge parallel to the first arcuate edge, and the side of the second pad opening close to the second arcuate edge is a fourth arcuate edge parallel to the second arcuate edge.

10. The pad steel mesh according to claim 9, characterized in that: When the solder paste is set on the welding substrate by the solder pad steel mesh, the minimum distance between the third arcuate edge of the first solder pad opening and the first arcuate edge is greater than or equal to 0.15 mm, and the minimum distance between the fourth arcuate edge of the second solder pad opening and the second arcuate edge is greater than or equal to 0.15 mm.

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