SMT conductive foam

Abstract

The utility model provides SMT conductive foam, and relates to the technical field of electronic assembly. The SMT conductive foam comprises an elastic core and a conductive layer, at least one through hole is formed in the SMT conductive foam in the length direction of the SMT conductive foam, a graph formed by connecting all the through holes is designed in an axial symmetry mode, and the area of all the through holes accounts for 25%-65% of the area of the whole cross section of the SMT conductive foam in the cross section perpendicular to the length direction of the SMT conductive foam. According to the SMT conductive foam, by optimizing the proportion of the area of the through holes in the whole sectional area, the stability of the foam can be improved, the foam still has a buffer space in the pressing process, the foam can still keep good aging resilience after being pressed for a long time in the environments of high temperature, high humidity and the like, the good recovery capacity is achieved, and the service life of the foam is prolonged. And meanwhile, the aging resistance and the rebound resilience are enhanced, the service life of the foam is prolonged, and the maintenance or replacement cost of an electronic product caused by the failure of the foam is reduced.

Description

Technical Field

[0001] This application relates to the field of electronic assembly technology, and more specifically, to an SMT conductive foam. Background Technology

[0002] SMT, or Surface Mount Technology, is primarily used in the electronics assembly industry, such as the mounting of components on printed circuit boards (PCBs). SMT technology can be adapted to automated equipment like robotic arms for rapid and efficient electronic assembly. For electronic components, electromagnetic compatibility (EMC) issues such as electromagnetic shielding and electrostatic discharge (ESD) protection are crucial, and the shock resistance of PCBs also affects their reliability and stability design. SMT conductive foam is precisely the EMC and shock-resistant component that enables high-speed SMT soldering, and it is widely used in the electronics assembly industry.

[0003] Existing surface-mount (SMT) conductive foam structures typically feature through-holes. These through-holes provide space for the SMT conductive foam to deform, and different through-hole structures exhibit different rebound forces under the same compression. In actual operation, SMT conductive foam may be subjected to prolonged pressure and high temperatures. During compression, the upper and lower walls of the SMT conductive foam come into contact, and small volatile molecules evaporate under high temperatures. Over time, the through-holes in the middle of the SMT conductive foam close. When the stress is relieved, the SMT conductive foam cannot return to its initial height, thus failing to ground or conduct electricity. The rebound performance of the SMT conductive foam decreases, ultimately causing the main function of the SMT conductive foam to fail, affecting the practical application of electronic products. Utility Model Content

[0004] The purpose of this application is to provide an SMT conductive foam that can improve the technical problems of easy pore closure and reduced resilience after long-term pressure under high temperature and high humidity environments.

[0005] In a first aspect, embodiments of this application provide an SMT conductive foam, which includes an elastic core and a conductive layer. The conductive layer covers at least a portion of the surface of the elastic core. The SMT conductive foam has at least one through hole along its length direction. The pattern formed by connecting all the through holes is axially symmetrical. On the cross-section of the SMT conductive foam perpendicular to its length direction, the area of ​​all the through holes accounts for 25% to 65% of the total cross-sectional area.

[0006] In the aforementioned implementation process, the SMT conductive foam of this application ensures good compression stability by designing all through-holes with an axisymmetric structure. Furthermore, by optimizing the ratio of the area of ​​all through-holes to the total cross-sectional area, it not only makes the internal stress of the SMT conductive foam more uniform, reducing local deformation and improving the stability of the foam, but also allows the foam to retain a certain buffer space during compression. The SMT conductive foam of this application maintains good aging resilience and recovery ability even after long-term compression under high temperature and high humidity environments, reducing the risk of through-hole closure. Simultaneously, due to the enhanced aging resistance and resilience, its service life is extended, reducing the repair or replacement costs of electronic products due to foam failure.

[0007] In one possible implementation, the area of ​​all through holes accounts for 30% to 45% of the total cross-sectional area.

[0008] In the above implementation process, by ensuring that the proportion of the area of ​​all through holes to the total cross-sectional area is within the above range, it is beneficial to further optimize the through hole area, obtain a large hole structure, ensure that the SMT conductive foam still has sufficient resilience after being compressed, and at the same time avoid excessive local stress concentration, which would cause the foam to fail prematurely.

[0009] In one possible implementation, the shape of the through hole includes regular or irregular shapes. Regular shapes include square, circular, elliptical, quadrilateral, or hexagonal shapes, while irregular shapes include arc-shaped inner edges or sloping inner edges.

[0010] In one possible implementation, the SMT conductive foam is designed to be axisymmetric.

[0011] In the above implementation process, this application makes the SMT conductive foam as a whole axisymmetric design, which helps to distribute stress more evenly after the foam is compressed, reducing the risk of local collapse.

[0012] In one possible implementation, the SMT conductive foam has a through hole, and the inner wall of the through hole includes a top inner wall, a first side wall, a bottom inner wall and a second side wall connected in sequence. The middle part of the bottom inner wall is formed as a groove structure or a protrusion structure, and / or; the middle part of the top inner wall is formed as a groove structure or a protrusion structure, and / or; the first side wall and the second side wall are formed as groove structures or protrusion structures.

[0013] In the above implementation process, this application forms a groove structure or a protrusion structure in the middle of the bottom inner wall to disperse the stress to both sides during compression, thereby preventing the SMT conductive foam from tilting due to uneven stress.

[0014] In one possible implementation, the elastic core has a bottom outer wall that slopes from the outer edge toward the center of the SMT conductive foam to form a recessed structure.

[0015] In the above implementation process, this application can ensure that the SMT conductive foam can more easily contact the PCB by forming a recessed structure in the middle of the bottom outer wall.

[0016] In one possible implementation, the inner wall of the through hole includes a top inner wall, a first side wall, a bottom inner wall, and a second side wall connected in sequence. The middle part of the bottom inner wall is formed into a groove structure or a protrusion structure, and the curvature of the groove structure or protrusion structure formed in the middle part of the bottom inner wall is greater than the curvature of the recess structure formed in the middle part of the bottom outer wall.

[0017] In the above implementation process, the larger curvature of the bottom inner wall structure can more flexibly fit the contact surface (such as PCB pads or metal shell) when compressed, so that the SMT conductive foam can distribute the pressure more evenly when compressed, and prevent tilting.

[0018] In one possible implementation, the minimum wall thickness of the elastic core is ≥0.4 mm.

[0019] In the above implementation process, this application improves the stress uniformity of the entire SMT conductive foam by keeping the minimum wall thickness of the elastic core within the above range, and can prevent the SMT conductive foam from collapsing during extrusion molding.

[0020] In one possible implementation, the conductive layer is a gold-plated polyimide structural layer, a copper-plated polyimide structural layer, a nickel-plated polyimide structural layer, or a tin-plated polyimide structural layer.

[0021] In one possible embodiment, the gold-plated polyimide structural layer comprises, from the inside out, a 10μm to 30μm polyimide layer, a 0.5μm to 10μm copper layer, a 0.01μm to 5μm nickel layer, and a gold layer greater than or equal to 0.01μm, and / or; the copper-plated polyimide structural layer comprises, from the inside out, a 10μm to 30μm polyimide layer and a 0.5μm to 10μm copper layer, and / or; the tin-plated polyimide structural layer comprises, from the inside out, a... The structure may consist of a 10μm to 30μm polyimide layer, a 0.5μm to 10μm copper layer, and a 0.1μm to 5μm tin layer, or a 10μm to 30μm polyimide layer, a 0.5μm to 10μm copper layer, a 0.01μm to 5μm nickel layer, and a 0.01μm to 5μm tin layer, and / or; the nickel-plated polyimide structural layer may consist of a 10μm to 30μm polyimide layer, a 0.5μm to 10μm copper layer, and a 0.01μm to 5μm nickel layer stacked sequentially from the inside out. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the structure of the first type of SMT conductive foam in the embodiments of this application;

[0024] Figure 2 This is a front view of the first type of SMT conductive foam according to the embodiments of this application;

[0025] Figure 3 This is a front view of the second type of SMT conductive foam according to an embodiment of this application;

[0026] Figure 4 This is a front view of the third type of SMT conductive foam according to an embodiment of this application;

[0027] Figure 5 This is a front view of the fourth type of SMT conductive foam according to the embodiments of this application;

[0028] Figure 6 This is a front view of the fifth type of SMT conductive foam according to the present application;

[0029] Figure 7 This is a front view of the sixth type of SMT conductive foam according to the present application;

[0030] Figure 8 This is a front view of the seventh type of SMT conductive foam in this application embodiment;

[0031] Figure 9 This is a front view of the SMT conductive foam of Comparative Example 1 of this application;

[0032] Figure 10 This is a front view of the SMT conductive foam of Comparative Example 2 of this application.

[0033] Icons: 10-SMT conductive foam; 100-elastic core; 101-through hole; 102-top inner wall; 103-first side wall; 104-bottom inner wall; 105-second side wall; 106-bottom outer wall; 200-conductive layer. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0035] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0036] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0037] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this application is in use. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0038] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0039] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0040] In the optimization of SMT conductive foam, the focus is mainly on the selection and improvement of materials. However, there is little research on optimizing the structure of SMT conductive foam itself and the through-hole structure to improve its resilience performance. Therefore, improving the through-hole structure to enhance the aging resilience performance of SMT conductive foam has important application value.

[0041] Please see Figures 1-8 Based on this, this application provides an SMT conductive foam 10, which includes an elastic core 100 and a conductive layer 200. The conductive layer 200 covers at least a portion of the surface of the elastic core 100. This covering can be partial or complete.

[0042] The elastic core 100 is a core component of the SMT conductive foam 10. Its main function is to provide mechanical support and elastic recovery while ensuring conductivity. The elastic core 100 is generally made of silicone rubber.

[0043] Optionally, the elastic core may also include high-temperature resistant fillers and / or flame-retardant fillers, wherein the high-temperature resistant fillers include at least one of alumina, silica and iron oxide, and the flame-retardant fillers include aluminum hydroxide and / or magnesium hydroxide.

[0044] As an example, the high-temperature resistant filler can be alumina alone, or silica alone, or a mixture of alumina and silica.

[0045] It should be noted that the high-temperature resistant filler is generally in granular or powder form and is added as a raw material when preparing the elastic core 100, and then molded.

[0046] This application improves the heat resistance of SMT conductive foam 10 by adding high-temperature resistant filler to the elastic core 100, thereby extending its service life and reducing the repair or replacement costs of electronic products due to foam failure.

[0047] The conductive layer 200 is a gold-plated polyimide structural layer, a nickel-plated polyimide structural layer, or a tin-plated polyimide structural layer.

[0048] The gold-plated polyimide structural layer comprises, from the inside out, a 10μm to 30μm polyimide layer, a 0.5μm to 10μm copper layer, a 0.01μm to 5μm nickel layer, and a gold layer greater than or equal to 0.01μm.

[0049] The copper-plated polyimide structural layer comprises a 10μm to 30μm polyimide layer and a 0.5μm to 10μm copper layer stacked sequentially from the inside out.

[0050] The tin-plated polyimide structural layer comprises, from the inside out, a 10μm to 30μm polyimide layer, a 0.5μm to 10μm copper layer, and a 0.1μm to 5μm tin layer, or a 10μm to 30μm polyimide layer, a 0.5μm to 10μm copper layer, a 0.01μm to 5μm nickel layer, and a 0.01μm to 5μm tin layer.

[0051] The nickel-plated polyimide structural layer comprises a 10μm to 30μm polyimide layer, a 0.5μm to 10μm copper layer, and a 0.01μm to 5μm nickel layer, which are stacked sequentially from the inside out.

[0052] The SMT conductive foam 10 has at least one through hole 101 along its length, and the pattern formed by all the through holes 101 is axially symmetrical. The length direction of the SMT conductive foam 10 is as follows: Figure 1 As shown in the L direction. The number of through holes can be, but is not limited to, 1, 2, 3, 4, 5, 6, 7, 8, or 9.

[0053] It should be noted that the through hole 101 can be formed inside the elastic core 100, such as... Figures 2-6 As shown in Figure 8, it can also be formed by defining an elastic core 100 and a conductive layer 200, such as... Figure 7 As shown.

[0054] like Figures 2-6 As shown, when the SMT conductive foam 10 includes a through hole 101, this through hole 101 is axially symmetrically distributed along its central axis of symmetry; as Figures 7-8 As shown, when the SMT conductive foam 10 includes at least two through holes 101, the shape and position of all through holes 101 are symmetrically arrayed along the middle of the SMT conductive foam 10 to ensure stability during use.

[0055] The shape of the through hole 101 can be a regular shape or an irregular shape. When the shape of the through hole 101 is a regular shape, the regular shape includes a square, a circle, an ellipse, a quadrilateral or a hexagon. When the shape of the through hole 101 is an irregular shape, the irregular shape includes an arc-shaped inner edge or an inclined inner edge.

[0056] It should be noted that when the through hole 101 has an irregular shape, the through hole 101 also needs to be designed to be axially symmetrical along its centerline. For example, the through hole 101 can be an axially symmetrical through hole 101 formed by the overlap of two identical circular parts.

[0057] In addition, the edges of the through-hole 101 can be straight or curved, and the corners can be right angles, rounded corners or chamfers. The rounded or chamfered design can reduce stress concentration and provide durability to the SMT conductive foam 10.

[0058] Optionally, the SMT conductive foam 10 has an overall axially symmetrical design.

[0059] When the SMT conductive foam 10 is designed to be axially symmetrical, the through hole 101 not only needs to be designed to be axially symmetrical, but also needs to be located on the geometric center axis of the elastic core 100.

[0060] This application makes the SMT conductive foam 10 as a whole axisymmetric design, which helps to distribute stress more evenly after the foam is compressed, reducing the risk of local collapse.

[0061] The shape of the cross-section of the SMT conductive foam 10 along its length direction includes a regular shape or an irregular shape. It should be noted that the shape of the cross-section of the SMT conductive foam 10 along its length direction refers to the shape of the outer contour of the cross-section of the SMT conductive foam 10 along its length direction, and does not include the shape of the internal through hole 101.

[0062] When the SMT conductive foam 10 has a regular shape along its cross-section perpendicular to its length direction, the regular shape includes rectangle, square, trapezoid, circle, ellipse or polygon to meet the needs of different pads or contact surfaces; when the SMT conductive foam 10 has an irregular shape along its cross-section perpendicular to its length direction, the irregular shape includes arc-shaped outer edge or inclined outer edge.

[0063] In addition, the edges of the outer contour of the SMT conductive foam 10 can be straight or curved, and the corners can be right angles, rounded corners or chamfers. The rounded corner or chamfer design can reduce stress concentration, provide durability to the SMT conductive foam 10, and reduce the risk of damage during assembly.

[0064] Alternatively, please continue reading Figures 2-8 The SMT conductive foam 10 has a through hole 101. The inner wall of the through hole 101 includes a top inner wall 102, a first side wall 103, a bottom inner wall 104 and a second side wall 105 connected in sequence. The bottom inner wall 104 is formed into a groove structure or a protrusion structure in the middle.

[0065] In this design, the top inner wall 102 refers to the top region of the inner wall surface of the through hole 101 on the mounting surface of the elastic core 100 (usually the side closer to the PCB); the first side wall 103 refers to the left side region of the inner wall surface of the through hole 101 on the mounting surface of the elastic core 100 (usually the side closer to the PCB); the bottom inner wall 104 refers to the bottom region of the inner wall surface of the through hole 101 on the mounting surface of the elastic core 100 (usually the side closer to the PCB); and the second side wall 105 refers to the right side region of the inner wall surface of the through hole 101 on the mounting surface of the elastic core 100 (usually the side closer to the PCB). The top inner wall 102 and the bottom inner wall 104 are positioned opposite each other, as are the first side wall 103 and the second side wall 105. Together, the top inner wall 102, the first side wall 103, the bottom inner wall 104, and the second side wall 105 constitute the inner wall of the entire through hole 101.

[0066] The middle part of the bottom inner wall 104 refers to the central area of ​​the bottom inner wall 104, which is used to bear the stress concentration during foam compression and prevent the bottom of the through hole 101 from tearing. This application forms the middle part of the bottom inner wall 104 into a groove structure or a protrusion structure to disperse the stress to both sides during compression, so as to avoid uneven stress on the SMT conductive foam 10 and tilting.

[0067] It should be noted that the grooved or raised structure and other areas of the bottom inner wall 104 transition smoothly.

[0068] Optionally, the middle part of the top inner wall 102 is formed as a groove structure or a protrusion structure.

[0069] Optionally, the first sidewall 103 and the second sidewall 105 are formed as a groove structure or a protrusion structure, and the elastic core 100 has a bottom outer wall 106 corresponding to the bottom inner wall 104. The bottom outer wall 106 is formed as a recessed structure by tilting from the outer edge toward the center of the SMT conductive foam.

[0070] During the soldering process, if the bottom of the SMT conductive foam 10 is a flat structure, some solder joints may lift or become suspended, leading to cold solder joints or poor soldering. This application, by forming a recessed structure in the middle of the bottom outer wall 106, ensures that the SMT conductive foam 10 can more easily contact the PCB around its perimeter.

[0071] In such Figures 2-5 In the embodiment shown, the middle part of the bottom inner wall 104 and the middle part of the top inner wall 102 are both formed as protruding structures, the first side wall 103 and the second side wall 105 are both formed as groove structures, and the bottom outer wall 106 is formed as a recessed structure by tilting from the outer edge toward the center of the SMT conductive foam.

[0072] In such Figure 6In the embodiment shown, the through hole 101 is rhomboid, and the middle of the bottom inner wall 104, the middle of the top inner wall 102, the middle of the first side wall 103, and the middle of the second side wall 105 are all formed into groove structures. The bottom outer wall 106 is inclined from the outer edge toward the center of the SMT conductive foam to form a recessed structure.

[0073] Alternatively, please continue reading Figures 2-5 The curvature of the groove or protrusion structure formed in the middle of the inner wall 104 is greater than the curvature of the recessed structure formed in the middle of the outer wall 106.

[0074] The larger curvature of the bottom inner wall 104 structure allows for more flexible contact with the contact surface (such as PCB pads or metal casing) during compression, enabling the SMT conductive foam to distribute pressure more evenly and prevent tilting.

[0075] The minimum wall thickness of the elastic core 100 is ≥0.4mm.

[0076] The minimum wall thickness of the elastic core 100 refers to the material thickness at the thinnest point of the inner wall of the through hole 101 of the elastic core 100.

[0077] As an example, the minimum wall thickness of the elastic core 100 includes, but is not limited to, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, or 1 mm.

[0078] By ensuring that the minimum wall thickness of the elastic core 100 is within the aforementioned range, this application helps to improve the uniformity of stress distribution on the entire SMT conductive foam 10 and prevents the SMT conductive foam 10 from collapsing during extrusion molding.

[0079] In the cross-section of the SMT conductive foam 10 along its length, the area of ​​all through holes 101 accounts for 25% to 65% of the total cross-sectional area.

[0080] It should be noted that the area of ​​all through holes 101 refers to the sum of the areas defined by the inner walls of the through holes 101, and the area of ​​the entire cross section refers to the sum of the cross-sectional area of ​​the elastic core 100, the cross-sectional area of ​​the conductive layer 200, and the area of ​​the through holes 101 along the length of the SMT conductive foam 10.

[0081] As an example, the area of ​​all through holes 101 includes, but is not limited to, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or 65% of the total cross-sectional area.

[0082] Optionally, the area of ​​all through holes 101 accounts for 30% to 45% of the total cross-sectional area.

[0083] By ensuring that the area of ​​all through holes 101 is within the above-mentioned range as a proportion of the total cross-sectional area, it is beneficial to further optimize the area of ​​through holes 101, obtain a large hole structure, ensure that the SMT conductive foam 10 still has sufficient resilience after being compressed, and at the same time avoid excessive local stress concentration, which would lead to premature failure of the foam.

[0084] The following describes in further detail an SMT conductive foam 10 of this application with reference to embodiments.

[0085] Example 1

[0086] Please see Figure 1 This application provides an SMT conductive foam 10, which includes an elastic core 100 and a conductive layer 200. The conductive layer 200 covers at least a portion of the surface of the elastic core 100. The elastic core 100 is made of silicone rubber and contains alumina high-temperature resistant filler. The conductive layer 200 is a gold-plated polyimide structure layer. The SMT conductive foam 10 has an irregular shape. The outer contour of the SMT conductive foam 10 has curved edges and chamfered corners. The SMT conductive foam 10 has an overall axially symmetrical design. The SMT conductive foam 10 has a through hole 101 along its length. The through hole 101 has an irregular shape. The contour of the through hole 101 has curved edges and chamfered corners. The inner wall of the through hole 101 includes a top inner wall 102, a first side wall 103, a bottom inner wall 104, and a second side wall 105 connected in sequence. The middle part of the bottom inner wall 104 and the middle part of the top inner wall 102 are both formed as protruding structures. The first side wall 103 and the second side wall 105 are both formed as groove structures. The elastic core 100 has a bottom outer wall 106 corresponding to the bottom inner wall 104. The middle part of the bottom outer wall 106 is formed as a recessed structure. The curvature of the groove structure or protruding structure formed in the middle of the bottom inner wall 104 is greater than the curvature of the recessed structure formed in the middle of the bottom outer wall 106. The minimum wall thickness of the elastic core 100 is ≥0.4mm. In the cross-section of the SMT conductive foam 10 along its length direction, the area of ​​the through hole 101 accounts for 36% of the total cross-sectional area.

[0087] Comparative Example 1

[0088] Please see Figure 9 This application provides an SMT conductive foam 10 as a comparative example, which changes the area of ​​the through hole 101 to 10% of the total cross-sectional area based on Example 1.

[0089] Comparative Example 2

[0090] Please see Figure 10 This application provides an SMT conductive foam 10 as a comparative example, which changes the area of ​​the through hole 101 to 20% of the total cross-sectional area based on Example 1.

[0091] Test case

[0092] Compression stress tests were conducted on Example 1 and Comparative Examples 1-2, with 40% compression at 125°C for 500 hours and 40% compression at 85°C & 85% humidity for 500 hours. The test results are shown in Tables 1-3.

[0093] The testing method is as follows:

[0094] 1. Compression stress test

[0095] Step 1: Pre-treat the sample in a laboratory environment (e.g., 23±2℃, 50±5% RH) for 24 hours;

[0096] Step 2: Place the sample in the center of the pressure plate and compress it at a constant rate (e.g., 5 mm / min) to the target compression ratio (e.g., 50%). Maintain constant pressure for 10 seconds and then read the stress data. Release the pressure immediately; the test is complete.

[0097] 2. Compression test at 40% and 125℃ for 500 hours.

[0098] Step 1: Measure the initial thickness T0 of the sample. Place the sample between the two plates of the test fixture, insert shims or feeler gauges with the thickness adjusted to T0 / 2 on both sides, and gradually tighten the screws at the four corners of the fixture to keep the sample thickness at 50%.

[0099] Step 2: Place the compressed sample in an oven at 125°C and keep it there for 500 hours;

[0100] Step 3: After baking for 500 hours, remove the sample and place it on a wooden board or a surface with low thermal conductivity.

[0101] Step 4: After cooling in a relaxed state for 30 minutes, measure the final thickness T1 of the sample.

[0102] Formula for calculating height loss:

[0103] CS = (T) O -T1) / T0*100%;

[0104] In the formula:

[0105] CS-------High loss rate (residual deformation);

[0106] T O -------Initial sample thickness, in millimeters (mm);

[0107] T1-----Sample springback thickness, in millimeters (mm).

[0108] 3. Compressed at 40% humidity, 85℃ & 85% humidity for 500 hours.

[0109] The test procedure is the same as the 500-hour test at 40% compression and 125℃, only the test environment is different. The test environment for this test is a constant temperature of 85℃ and a relative humidity of 85% (5RH).

[0110] Table 1 Comparison of compressive stress tests

[0111]

[0112] Table 2. Test at 40% compression and 125℃ for 500 hours.

[0113] project Example 1 Comparative Example 1 Comparative Example 2 High loss rate (%) 3.5％ 17.0％ 8.1％

[0114] Table 3. Test at 40% compression, 85℃ & 85% humidity for 500 hours.

[0115] project Example 1 Comparative Example 1 Comparative Example 2 High loss rate (%) 2.9％ 23.5％ 7.2％

[0116] In Example 1, the area of ​​the through-hole 101 of the SMT conductive foam 10 accounts for 36% of the total cross-sectional area; in Comparative Example 1, the area of ​​the through-hole 101 of the SMT conductive foam 10 accounts for 10% of the total cross-sectional area; and in Comparative Example 2, the area of ​​the through-hole 101 of the SMT conductive foam 10 accounts for 20% of the total cross-sectional area.

[0117] As shown in Table 1, the SMT conductive foam 10 of Example 1 has a greater compressive stress at a compression rate of 10% than the SMT conductive foam 10 of Comparative Examples 1 and 2; the SMT conductive foam 10 of Example 1 has a greater compressive stress at a compression rate of 20% than the SMT conductive foam 10 of Comparative Examples 1 and 2; the SMT conductive foam 10 of Example 1 has a greater compressive stress at a compression rate of 30% than the SMT conductive foam 10 of Comparative Examples 1 and 2; the SMT conductive foam 10 of Example 1 has a greater compressive stress at a compression rate of 40% than the SMT conductive foam 10 of Comparative Examples 1 and 2; and the SMT conductive foam 10 of Example 1 has a greater compressive stress at a compression rate of 50% than the SMT conductive foam 10 of Comparative Examples 1 and 2.

[0118] As shown in Table 2, the height loss rate of the SMT conductive foam 10 in Example 1 after 500 hours of testing at 125°C with a compression of 40% is much lower than that of the SMT conductive foam 10 in Comparative Examples 1 and 2 after 500 hours of testing at 125°C with a compression of 40%.

[0119] As shown in Table 3, the height loss rate of the SMT conductive foam 10 in Example 1 after 500 hours of testing at 40% compression and 85°C & 85% humidity is much lower than that of the SMT conductive foam 10 in Comparative Examples 1-2 after 500 hours of testing at 40% compression and 85°C & 85% humidity.

[0120] In summary, the SMT conductive foam 10 of this application, on the one hand, ensures good compression stability by making the pattern formed by all the through holes 101 axially symmetrical; on the other hand, by optimizing the ratio of the area of ​​all the through holes 101 to the total cross-sectional area, it not only makes the internal stress of the SMT conductive foam 10 more uniform, reduces local deformation, and improves the stability of the foam, but also allows the foam to still have a certain buffer space during compression. The SMT conductive foam 10 of this application can maintain good aging resilience and recovery ability after long-term compression in high temperature and high humidity environments, reducing the risk of through hole 101 closure. Furthermore, due to the enhanced aging resistance and resilience, its service life is extended, reducing the repair or replacement costs of electronic products caused by foam failure.

[0121] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An SMT conductive foam, characterized in that, The SMT conductive foam includes an elastic core and a conductive layer. The conductive layer covers at least a portion of the surface of the elastic core. The SMT conductive foam has at least one through hole along its length. The pattern formed by connecting all the through holes is axially symmetrical. On the cross-section of the SMT conductive foam perpendicular to its length, the area of ​​all the through holes accounts for 25% to 65% of the total cross-sectional area.

2. The SMT conductive foam according to claim 1, characterized in that, The area of ​​all the through holes accounts for 30% to 45% of the total cross-sectional area.

3. The SMT conductive foam according to claim 1, characterized in that, The shape of the through hole can be regular or irregular. The regular shape includes square, circle, ellipse, quadrilateral or hexagonal, and the irregular shape includes arc-shaped inner edge or inclined inner edge.

4. The SMT conductive foam according to claim 1, characterized in that, The elastic core is designed with axisymmetric symmetry.

5. The SMT conductive foam according to claim 1, characterized in that, The SMT conductive foam has a through hole, and the inner wall of the through hole includes a top inner wall, a first side wall, a bottom inner wall and a second side wall connected in sequence. The middle part of the bottom inner wall is formed into a groove structure or a protrusion structure, and / or; The middle part of the top inner wall is formed as a groove structure or a protrusion structure, and / or; The first sidewall and the second sidewall are formed as a groove structure or a protrusion structure.

6. The SMT conductive foam according to claim 1, characterized in that, The elastic core has a bottom outer wall, which is inclined from the outer edge toward the center of the SMT conductive foam to form a recessed structure.

7. The SMT conductive foam according to claim 6, characterized in that, The inner wall of the through hole includes a top inner wall, a first side wall, a bottom inner wall, and a second side wall connected in sequence. The middle part of the bottom inner wall is formed into a groove structure or a protrusion structure, and the curvature of the groove structure or protrusion structure formed in the middle part of the bottom inner wall is greater than the curvature of the concave structure formed in the middle part of the bottom outer wall.

8. The SMT conductive foam according to claim 1, characterized in that, The minimum wall thickness of the elastic core is ≥0.4mm.

9. The SMT conductive foam according to claim 1, characterized in that, The conductive layer is a gold-plated polyimide structural layer, a copper-plated polyimide structural layer, a nickel-plated polyimide structural layer, or a tin-plated polyimide structural layer.

10. The SMT conductive foam according to claim 9, characterized in that, The gold-plated polyimide structural layer comprises, from the inside out, a 10μm to 30μm polyimide layer, a 0.5μm to 10μm copper layer, a 0.01μm to 5μm nickel layer, and a gold layer greater than or equal to 0.01μm, and / or, stacked sequentially. The copper-plated polyimide structural layer comprises a 10μm to 30μm polyimide layer and a 0.5μm to 10μm copper layer stacked sequentially from the inside to the outside, and / or; The tin-plated polyimide structural layer comprises, from the inside out, a 10μm to 30μm polyimide layer, a 0.5μm to 10μm copper layer, and a 0.1μm to 5μm tin layer, or a 10μm to 30μm polyimide layer, a 0.5μm to 10μm copper layer, a 0.01μm to 5μm nickel layer, and a 0.01μm to 5μm tin layer, and / or; The nickel-plated polyimide structural layer comprises a 10μm to 30μm polyimide layer, a 0.5μm to 10μm copper layer, and a 0.01μm to 5μm nickel layer, arranged sequentially from the inside out.

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