CN114374101A

CN114374101A - Connection structure and method of forming a connection structure

Info

Publication number: CN114374101A
Application number: CN202210031345.8A
Authority: CN
Inventors: 陈忠君; 姚念
Original assignee: Interface Optoelectronics Shenzhen Co Ltd; Interface Technology Chengdu Co Ltd; Yecheng Optoelectronics Wuxi Co Ltd; General Interface Solution Ltd
Current assignee: Interface Optoelectronics Shenzhen Co Ltd; Interface Technology Chengdu Co Ltd; Yecheng Optoelectronics Wuxi Co Ltd; General Interface Solution Ltd
Priority date: 2022-01-12
Filing date: 2022-01-12
Publication date: 2022-04-19
Also published as: TW202328378A

Abstract

A connecting structure includes: the electronic device comprises a first electronic component, a buffer layer, an anisotropic conductive film and a second electronic component. The first electronic component includes a first substrate and a first conductive element on the first substrate. The buffer layer is disposed on an upper surface of the first conductive element. The anisotropic conductive adhesive film comprises an insulating adhesive layer and first conductive particles in the insulating adhesive layer, wherein the insulating adhesive layer is arranged on the buffer layer. The second electronic assembly is arranged above the first electronic assembly, is arranged on the anisotropic conductive film and comprises a second substrate and a second conductive element below the second substrate, and the first conductive particles are electrically connected with the first conductive element and the second conductive element. The thermal expansion coefficient of the buffer layer is between that of the first conductive element and that of the insulating glue layer. Methods of forming the connection structures are also provided.

Description

Connection structure and method of forming a connection structure

Technical Field

The present disclosure relates to a connection structure with anisotropic conductive film and a method for forming the same.

Background

Anisotropic Conductive Film (ACF) is widely used in processes unsuitable for high temperature soldering, such as the press-fit connection between Integrated Circuit (IC) and Liquid Crystal Display (LCD), Flexible Printed Circuit (FPC) and LCD, and between IC and Film, to achieve signal transmission and image display. The anisotropic conductive film is a transparent polymer connecting material with the characteristics of adhesion, conductivity and insulation, and is characterized in that the film is conducted in the Z direction (vertical direction) and insulated in the XY direction (horizontal direction), so that the problem of fine wire connection which can not be processed by some connectors can be solved.

The lamination integrity and reliability of the anisotropic conductive film are particularly important. However, in the conventional connection structure of the anisotropic conductive film, after a period of use or when a reliability test such as a pressure cooking test is performed, it is found that cracks are likely to occur at the interface of the anisotropic conductive film, resulting in electrical failure.

Disclosure of Invention

Some embodiments of the present disclosure provide a connection structure including a first electronic component, a buffer layer, an anisotropic conductive film, and a second electronic component. The first electronic component includes a first substrate and a first conductive element over the first substrate. The buffer layer is disposed on an upper surface of the first conductive member of the first electronic assembly. The anisotropic conductive film includes an insulating glue layer and first conductive particles in the insulating glue layer, wherein the insulating glue layer is disposed over the first substrate and the first conductive element of the first electronic component and on the buffer layer. The second electronic assembly is disposed on the anisotropic conductive film, and includes a second substrate and a second conductive element under the second substrate, the second conductive element contacting the first conductive particles. The thermal expansion coefficient of the buffer layer is between that of the first conductive element and that of the insulating glue layer of the anisotropic conductive glue film.

In some embodiments, the buffer layer has a coefficient of thermal expansion of about 20ppm/K to about 50ppm/K in the connection structure.

In some embodiments, in the connection structure, the buffer layer includes an organic thin film, a metal plating layer, or a combination thereof.

In some embodiments, in the connection structure, the buffer layer includes an organic thin film, and the first conductive particles pass through the buffer layer to electrically connect the first conductive elements.

In some embodiments, in the connection structure, the buffer layer includes an organic thin film, and a material of the organic thin film is Rosin (Rosin), Active Resin (Active Resin), Azole (Azole), polyether ether ketone, polyimide, or acrylic Resin.

In some embodiments, in the connection structure, the anisotropic conductive film further includes second conductive particles in the insulating glue layer, the second conductive particles do not contact the first conductive element and the second conductive element, and the buffer layer has a thickness of about 1/20 to about 1/5 of a height of the second conductive particles.

In some embodiments, the connecting structure comprises a metal coating, the material of the metal coating being zinc, aluminum, magnesium, lead, cadmium, or a combination thereof.

In some embodiments, in the connection structure, the buffer layer includes a metal plating layer and an organic thin film disposed over the metal plating layer.

In some embodiments, in the connection structure, the buffer layer is also disposed on a side surface of the first conductive element.

In some embodiments, the buffer layer is also disposed on the side surface of the first conductive member and on the first substrate.

In some embodiments, in the connection structure, a thermal expansion coefficient of the first substrate is smaller than a thermal expansion coefficient of the second substrate.

In some embodiments, in the connection structure, a coefficient of thermal expansion of the first conductive element is less than a coefficient of thermal expansion of the second conductive element.

In some embodiments, the first conductive particles have a horizontal dimension of between about 5 microns and about 40 microns in the connection structure.

Some embodiments of the present disclosure provide a method of forming a connection structure, comprising: a first electronic component is provided, wherein the first electronic component includes a first substrate and a first conductive element over the first substrate. Disposing a buffer layer on an upper surface of a first conductive element of a first electronic component; arranging an anisotropic conductive adhesive film above the buffer layer, wherein the anisotropic conductive adhesive film comprises an insulating adhesive layer and first conductive particles in the insulating adhesive layer; arranging a second electronic component above the anisotropic conductive adhesive film, wherein the second electronic component comprises a second substrate and a second conductive element below the second substrate, and the thermal expansion coefficient of the buffer layer is between the thermal expansion coefficient of the first conductive element and the thermal expansion coefficient of the insulating adhesive layer of the anisotropic conductive adhesive film; and laminating the first electronic component, the buffer layer, the anisotropic conductive film and the second electronic component, wherein the first conductive particles of the anisotropic conductive film are electrically connected with the first conductive element and the second conductive element.

In some embodiments, in the method of forming the connection structure, providing the buffer layer is via a soft-to-hard lamination technique or an organic soldermask technique.

In some embodiments, in the method of forming the connection structure, the buffer layer includes an organic film, and the first conductive particles of the anisotropic conductive film penetrate through the organic film to electrically connect the first conductive elements when the first electronic component, the buffer layer, the anisotropic conductive film, and the second electronic component are laminated.

In some embodiments, in the method of forming a connection structure, the buffer layer includes a metal plating layer, and the first conductive particles of the anisotropic conductive film are electrically connected to the first conductive elements by contacting the metal plating layer when the first electronic component, the buffer layer, the anisotropic conductive film, and the second electronic component are laminated.

In some embodiments, in the method of forming a connection structure, the buffer layer is an organic thin film, and the buffer layer has a thickness of between about 1 micron and about 4 microns.

Drawings

In order to make the aforementioned and other objects, features, advantages and embodiments of the disclosure more comprehensible, the following description is given:

fig. 1 illustrates a cross-sectional view of a connection structure according to some embodiments.

Fig. 2 is a cross-sectional view according to a comparative example.

Fig. 3 is a stress diagram simulated by a multi-physical quantity coupling analysis software according to the comparative example of fig. 2.

Fig. 4 is a cross-sectional view according to an experimental example.

Fig. 5 is a stress diagram simulated by a multi-physical quantity coupling analysis software according to the experimental example of fig. 4.

Fig. 6A-6E are various cross-sectional views at various intermediate stages of forming a connection structure according to some embodiments.

Fig. 7A, 7B are enlarged cross-sectional views at various intermediate stages of forming a connection structure according to some embodiments.

Fig. 8 depicts a cross-sectional view of a connection structure according to some alternative embodiments.

Fig. 9 depicts a flow diagram of a method of forming an organic soldermask in accordance with some embodiments.

Fig. 10 depicts a cross-sectional view of a connection structure according to some alternative embodiments.

Fig. 11 depicts a cross-sectional view of a connection structure according to some alternative embodiments.

Fig. 12 depicts a cross-sectional view of a connection structure according to some alternative embodiments.

Fig. 13 depicts a cross-sectional view of a connection structure according to some alternative embodiments.

Fig. 14 depicts a cross-sectional view of a connection structure according to some alternative embodiments.

Reference numerals:

100 connection structure 110 first electronic component

112 first substrate 114 first conductive element

120 buffer layer 130 anisotropic conductive film

132 insulating glue layer 134 first conductive particles

136 second conductive particles 140 second electronic component

142 a second substrate 144 a second conductive element

300 connecting structure 310 rigid substrate

320 anisotropic conductive film 330 flexible substrate

500 connecting structure 510 rigid substrate

520 buffer layer 530 anisotropic conductive film

540 flexible substrate 700 connection Structure

710 first electronic component 712 first substrate

714 first conductive element 720 buffer layer

730 anisotropic conductive film 732 insulating adhesive layer

734 first conductive particles 736 second conductive particles

740 second electronic component 742 and second substrate

744 second conductive element 800 connection Structure

820 buffer layer 820A first portion

820B second portion 900 method

902. 904, 906, 908, 910, 912, 914, 916, 918: step (ii) of

1000 connection structure 1020 buffer layer

1020A, first portion 1020B, second portion

1100 connecting structure 1120 buffer layer

1200 connecting structure 1220 buffer layer

1300 connection structure 1320 first buffer layer

1322 second buffer layer 1400 connecting structure

1420 first buffer layer 1422 second buffer layer

H1 height H2 height

P1 pressing force

Detailed Description

In order to make the description of the present disclosure more complete and complete, the following description is given for illustrative purposes, and for describing particular embodiments of the present disclosure; it is not intended to be the only form in which an embodiment of the present disclosure may be practiced or utilized. The various embodiments disclosed below may be combined with or substituted for one another where appropriate, and additional embodiments may be added to one embodiment without further recitation or description.

In the following description, numerous specific details are set forth to provide a thorough understanding of the following embodiments. However, embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known structures and devices are shown schematically in order to simplify the drawing.

Additionally, the present disclosure may repeat reference numerals and/or letters in the various embodiments. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Furthermore, in the following disclosure, one feature may be formed on, connected to, and/or coupled to another feature, and may include embodiments in which the features are in direct contact, and may also include embodiments in which another feature may be formed and interposed between the features, such that the features may not be in direct contact.

Furthermore, spatially relative terms, such as "upper," "lower," "above," "below," and the like, may be used herein to describe one element or feature's relationship to another element or feature in the drawings. These spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. Devices may also be translated in other orientations (rotated 90 degrees or other orientations) and thus the spatially relative descriptors used herein should be interpreted similarly.

In a conventional connection structure with an anisotropic conductive film, the anisotropic conductive film is disposed between two electronic components and directly contacts the substrate and the circuit of the two electronic components. After the process of bonding the anisotropic conductive film is completed, a reliability Test, such as a Pressure Cooker Test (PCT), is performed, and the device under Test is placed under severe temperature, saturated humidity (saturated water vapor), and high Pressure environment conditions for testing, so as to evaluate the damage of the device under Test on the interface of the molding compound or the electronic component under high temperature, high humidity, and high Pressure conditions. And then checking whether the device to be tested has electrical failure.

According to some experimental examples of the present disclosure, a conventional connection structure having an anisotropic conductive film is tested, in which the connection structure connects an electronic component having a rigid substrate and a circuit (i.e., a conductive element or a conductive pad) and another electronic component having a flexible circuit board and a circuit by using the anisotropic conductive film. When a conventional dut having a connection structure of an anisotropic conductive film is placed in an environment of 121 ℃, 100% relative humidity, and 205Kpa for 4 hours, it is found that cracks occur at the interface of the anisotropic conductive film, and thus the electrical function of the dut fails. And the occurrence of peeling gaps can be observed by a scanning electron microscope, and the peeling gaps are concentrated at the interface between the anisotropic conductive film and the conductive element of the electronic component.

Because the thermal expansion coefficient of the anisotropic conductive film is greatly different from that of the conductive element or the substrate of the electronic component, when a plurality of materials with different thermal expansion coefficients form a device, the temperature change generates stress due to inconsistent thermal expansion degrees. Therefore, at the interface having a high difference in thermal expansion coefficient, the problem of interface peeling is easily caused by stress generated by a temperature rise.

The disclosure relates to an improvement method of an anisotropic conductive film lamination process, which adds a buffer layer between the stress concentration interface, i.e. the anisotropic conductive film and a first electronic component, wherein the thermal expansion coefficient of the buffer layer is between the thermal expansion coefficient of the anisotropic conductive film and the thermal expansion coefficient of a conductive element of the first electronic component, so as to buffer the strain effect between different interfaces, and the stress strain gradient is distributed between the anisotropic conductive film and the buffer layer and between the buffer layer and the conductive element. Therefore, the problem of interface peeling due to temperature rise is reduced.

Referring to fig. 1, a cross-sectional view of a connection structure according to some embodiments is illustrated. The connection structure 100 includes a first electronic component 110, a buffer layer 120, an anisotropic conductive film 130, and a second electronic component 140.

The first electronic component 110 includes a first substrate 112 and a plurality of first conductive elements 114 over the first substrate 112. In some embodiments, the first conductive element 114 covers a surface of a portion of the first substrate 112. The buffer layer 120 is disposed over the first electronic component 110, covering the first substrate 112 and the plurality of first conductive elements 114. The anisotropic conductive film 130 includes an insulating adhesive layer 132 and first conductive particles 134 and second conductive particles 136 in the insulating adhesive layer 132. Height H of first conductive particles 134₁Lowered by the press-fit action and configured to electrically connect the first conductive element 114 of the first electronic component 110 and the conductive element of the second electronic component 140. The first conductive particles 134 penetrate the buffer layer 120 to physically and electrically connect the first conductive elements 114 of the first electronic component 110. The second conductive particles 136 are located at the first conductive element 114 and the second electronic component that are not in the vertical direction (i.e., the Z direction) with the first electronic component 110The conductive elements of member 140 overlap and are surrounded by the layer of insulating glue 132. That is, the second conductive particles 136 do not overlap with the area of the first electronic component 110, which is vertically projected onto the first substrate 112, of the first conductive element 114, and also do not overlap with the area of the second conductive element 144, which is vertically projected onto the first substrate 112, of the second electronic component 140, of the second conductive particle 136. In other words, the second conductive particles 136 are located between the first substrate 112 and the second substrate 142 and are not deformed by the pressing action to reduce the height. As shown in fig. 1, the second conductive particles 136 have a height H₂And the height H of the first conductive particles₁Is smaller than the height H of the second conductive particles 136₂. The second electronic assembly 140 is disposed on the anisotropic conductive film 130 and includes a second substrate 142 and a plurality of second conductive elements 144 under the second substrate 142. In some embodiments, the second conductive element 144 covers a surface of a portion of the second substrate 142. The first conductive element 114 and the second conductive element 144 overlap in the vertical direction, and the second conductive element 144 is physically and electrically connected to the first conductive particles 134. That is, the second conductive element 144 overlaps the first conductive particles 134 and the first conductive element 114 in the vertical projection with the area of the first substrate 112. In some embodiments, the first conductive element 114 may have a size that is less than, about equal to, or greater than the size of the second conductive element 144. As shown in fig. 1, the first conductive element 114 and the second conductive element 144 are electrically connected via the first conductive particles 134.

In some embodiments, the first substrate 112 of the first electronic component 110 is a rigid substrate, and the second substrate 142 of the second electronic component 140 is a flexible substrate; the present disclosure is not limited thereto and the buffer layer of the present disclosure may be applied to an interface having a large difference in thermal expansion coefficient.

In some embodiments, the thermal expansion coefficients of the first conductive element 114 of the first electronic component 110 and the second conductive element 144 of the second electronic component 140 are both smaller than the thermal expansion coefficient of the insulating adhesive layer 132 of the anisotropic conductive film 130. In some embodiments, the coefficient of thermal expansion of the first conductive element 114 of the first electronic component 110 is less than the coefficient of thermal expansion of the second conductive element 144 of the second electronic component 140; that is, the difference between the thermal expansion coefficients of the adhesive layer 132 and the first conductive element 114 is greater than the difference between the thermal expansion coefficients of the adhesive layer 132 and the second conductive element 144.

In some embodiments, the thermal expansion coefficients of the first substrate 112 of the first electronic component 110 and the second substrate 142 of the second electronic component 140 are both smaller than the thermal expansion coefficient of the insulating adhesive layer 132 of the anisotropic conductive film 130, and the thermal expansion coefficient of the first substrate 112 of the first electronic component 110 is smaller than the thermal expansion coefficient of the second substrate 142 of the second electronic component 140. That is, the difference in the thermal expansion coefficient between the insulating glue layer 132 and the first substrate 112 is larger than the difference in the thermal expansion coefficient between the insulating glue layer 132 and the second substrate 142.

The buffer layer 120 is disposed between the first conductive element 114 and the insulating adhesive layer 132, which have a larger difference between the thermal expansion coefficients, and the thermal expansion coefficient of the buffer layer 120 is between the thermal expansion coefficient of the first conductive element 114 and the thermal expansion coefficient of the insulating adhesive layer 132, so that the strain gradient of the stress caused by the temperature rise can be distributed to the interface between the first conductive element 114 and the buffer layer 120 and the interface between the buffer layer 120 and the insulating adhesive layer 132.

In addition, the buffer layer 120 is also disposed between the first substrate 112 and the insulating adhesive layer 132 having a large difference in thermal expansion coefficient, and the thermal expansion coefficient of the buffer layer 120 is between that of the first substrate 112 and that of the insulating adhesive layer 132, so that the strain gradient of the stress caused by the temperature rise can be distributed between the interface between the first substrate 112 and the buffer layer 120 and the interface between the buffer layer 120 and the insulating adhesive layer 132.

It is noted that although fig. 1 illustrates the buffer layer 120 as covering the upper surface and the side surfaces of the first conductive element 114 and the upper surface of the first substrate 112, in some embodiments, the buffer layer 120 may cover only the upper surface of the first conductive element 114 or only the upper surface and the side surfaces of the first conductive element 114, depending on the manufacturing process. Since the electrical function of the device is disabled once the peeling occurs between the adhesive layer and the first conductive element, the buffer layer 120 is preferably disposed between the adhesive layer 132 and the first conductive element 114, particularly between the adhesive layer 132 and the upper surface of the first conductive element 114.

Some examples are described below to illustrate that the connection structure of the present disclosure can reduce the peeling phenomenon between the anisotropic conductive film and the substrate through the provision of the buffer layer.

Referring to the table one below, the minimum peel strength of three different anisotropic conductive films at different bonding temperatures was obtained through the peel test. In the peeling test, three different anisotropic conductive films are sample (i), sample (ii), and sample (iii), respectively. Each sample to be tested had a length of 1.168 cm and a width of 0.716 cm. In the peel test, a part of the sample was peeled off in the longitudinal direction, and then the peel strength of the sample was measured. The table one below shows the lowest peel strengths obtained under the different test conditions.

Watch 1

According to the maximum normal stress criterion (also referred to as the first strength theory or the maximum tensile stress theory), the material fracture is caused by the maximum tensile stress, that is, the material fractures when the maximum tensile stress reaches a certain limit value. The maximum normal stress causing the destruction (peeling) of the anisotropic conductive film was calculated by using the median of the maximum minimum peel strengths measured, i.e., 1.6kgf/cm, according to the peel strength test under the above different conditions. I.e. the failure condition σ₁＝σ_bt＝1.6*9.81/0.716＝21.92N/cm。

FIG. 2 shows a comparative example. The connecting structure 300 includes a rigid substrate 310, an anisotropic conductive film 320 on the rigid substrate 310, and a flexible substrate 330 on the anisotropic conductive film 320. The rigid substrate 310 is made of alumina ceramic and has a thermal expansion coefficient of 7.1 ppm/K.The material of the insulating layer in the anisotropic conductive film 320 is Acrylic (Acrylic), and the thermal expansion coefficient of the anisotropic conductive film 320 is 169 ppm/K. The flexible substrate 330 comprises a DuPont

Black polyimide film and DuPont

Black flexible circuit board material, and dupont thereof

The black polyimide film had a thermal expansion coefficient of 10ppm/K, while DuPont

The thermal expansion coefficient of the black flexible circuit board material is 25 ppm/K; in the test of this comparative example, DuPont

The black flexible printed circuit board material is a portion in contact with the anisotropic conductive film 320. Therefore, the difference between the thermal expansion coefficients of the rigid substrate 310 and the anisotropic conductive film 320 is 22.8 times, and the difference between the thermal expansion coefficients of the anisotropic conductive film 320 and the flexible substrate 330 is 5.76 times.

Then using multiple physical quantity coupling analysis software (COMOSOL)

) The temperature change simulation was performed to find that the normal stress between the rigid substrate 310 and the anisotropic conductive film 320 was 26.59N/cm and the normal stress between the anisotropic conductive film 320 and the flexible substrate 330 was 22.60 when the temperature of the device increased from 25 ℃ to 121 ℃. Referring to fig. 3, it is shown that the normal stress between the rigid substrate 310 and the anisotropic conductive film 320 is 26.59N/cm when the temperature is 121 ℃. In addition, the simulation experiment shows that the shearing force between the rigid substrate 310 and the anisotropic conductive film 320 is-15.38N/cm。

That is, on the side of the anisotropic conductive film 320 close to the rigid substrate 310, the normal stress is 26.59N/cm, which is significantly higher than the failure condition σ_bt(i.e., 21.92N/cm). Therefore, when the temperature rises, the anisotropic conductive film 320 is likely to be peeled off from the side close to the rigid substrate 310 due to the stress caused by the temperature change.

FIG. 4 shows an experimental example. The connection structure 500 includes a rigid substrate 510, a buffer layer 520 on the rigid substrate 510, an anisotropic conductive film 530 on the buffer layer 520, and a flexible substrate 540 on the anisotropic conductive film 530. The rigid substrate 510 was made of alumina ceramic and had a thermal expansion coefficient of 7.1 ppm/K. The material of the buffer layer 520 is acrylic resin, and the thermal expansion is 34.6 ppm/K. The material of the insulating layer in the anisotropic conductive film 530 is Acrylic (Acrylic), and the thermal expansion coefficient of the anisotropic conductive film 530 is 169 ppm/K. The flexible substrate 540 comprises a DuPont

Black polyimide film and DuPont

Black flexible circuit board material, and dupont thereof

The thermal expansion coefficient of the black flexible circuit board material is 25 ppm/K; in the test of this experimental example, DuPont

The black flexible printed circuit board material is a portion in contact with the anisotropic conductive film 530. Therefore, the difference between the thermal expansion coefficients of the rigid substrate 510 and the buffer layer 520 is 4.87 times, which is between the buffer layer 520 and the anisotropic conductive adhesiveThe difference between the thermal expansion coefficients of the films 530 is 4.88 times, and the difference between the thermal expansion coefficients of the anisotropic conductive film 530 and the flexible substrate 540 is 5.76 times.

Then using multiple physical quantity coupling analysis software (COMOSOL)

) The temperature change simulation was performed to find that the normal stress between the buffer layer 520 and the anisotropic conductive film 530 was-0.65N/cm when the temperature of the device was increased from 25 ℃ to 121 ℃. Referring to fig. 5, it is shown that the normal stress between the rigid substrate 510 and the buffer layer 520 is-0.65N/cm when the temperature is 121 ℃. In addition, the simulation results in a shear force between the rigid substrate 510 and the buffer layer 520 of 6.48N/cm. That is, the normal stress on the anisotropic conductive film 530 closer to the rigid substrate 510 is significantly reduced by the buffer layer 520, which is much smaller than the failure condition σ_bt(i.e., 21.92N/cm) and less than the normal stress of the anisotropic conductive film 530 on the side close to the flexible substrate 540. Therefore, the phenomenon of peeling damage concentrated on the side of the anisotropic conductive film 530 near the rigid substrate 510 is improved.

Fig. 6A-6E illustrate cross-sectional views of intermediate stages of forming a connection structure, according to some embodiments.

Referring to FIG. 6A, the provision of the first electronic component in this step is shown. The first electronic component 710 includes a first substrate 712 and a plurality of first conductive elements 714 over the first substrate 712.

In some embodiments, the first substrate 712 may be a rigid substrate, such as a paper substrate, a glass cloth substrate, a synthetic fiber cloth substrate, a non-woven fabric substrate, a composite substrate, and the like.

In some embodiments, the material of the first conductive element 714 can include conductive materials such as gold, silver, copper, aluminum, indium tin oxide, and the like.

Referring to fig. 6B, a buffer layer is disposed on the first electronic component. The buffer layer 720 is disposed over the first substrate 712 and the first conductive element 714 of the first electronic component 710. The buffer layer 720 is an organic thin film having a thermal expansion coefficient between that of the first substrate 712 and that of the subsequently formed insulating glue layer, for example, about 20 to about 50 ppm/K. In some embodiments, the material of the buffer layer 720 is Rosin (Rosin), Active Resin (Active Resin), Azole (Azole), polyetheretherketone, polyimide, or acrylic Resin.

In some embodiments, buffer layer 720 has a thickness of about 1 micron to about 4 microns, preferably about 1.5 microns to about 3 microns, more preferably about 1.8 microns to about 2.2 microns, for example about 2 microns. In some embodiments, the thickness of the buffer layer 720 is about 1/20 to about 1/5, preferably about 1/10, of the height of the conductive particles (before lamination) of the anisotropic conductive film disposed subsequently, so as to provide a suitable stress buffering effect and enable the conductive particles to penetrate through the buffer layer 720 during lamination. In some embodiments, the material of the buffer layer 720 may be disposed over the first substrate 712 and the first conductive element 714 of the first electronic component 710 by coating. In some embodiments, the organic thin film may be attached to the first electronic component 710 via Soft-to-Hard (STH) technology.

In embodiments where the organic film is applied via soft-to-hard techniques, a polyetheretherketone film having a coefficient of thermal expansion of about 20 to 50ppm/K can be applied over the first electronic component 710; alternatively, a polyimide film or an acrylic film having a coefficient of thermal expansion of about 30 to 40ppm/K (e.g., about 34.6ppm/K) may be attached to the first electronic component 710.

Referring to fig. 6C, the anisotropic conductive film is disposed on the buffer layer. The anisotropic conductive film 730 includes an insulating adhesive layer 732 and first conductive particles 734 and second conductive particles 736 distributed in the insulating adhesive layer 732. The insulating layer 732 is adhesive, heat-resistant, and insulating, and can fix the relative positions of the conductive elements and maintain the contact area between the conductive elements and the conductive particles. In some embodiments, the material of the insulating glue layer 732 may include a thermosetting resin epoxy resin, such as acryl, or various bisphenol a type epoxy resins, such as E-44, E-20, E-51, etc., but the disclosure is not limited thereto. In some embodiments, the insulating glue layer 732 further comprises additives such as curing agents, cross-linking agents, diluents, photoinitiators, coupling agents, and the like.

In some embodiments, the first and second

conductive particles

734 and 736 are polymer microspheres coated with a conductive metal. The material of the polymeric microspheres may be for example, but not limited to: polyethylene, polypropylene, polyester, polystyrene, polyvinyl alcohol, or polymethyl methacrylate. The conductive metal can be, for example, nickel, gold, copper, silver, tin, lead, aluminum, tungsten, iron, the like, or combinations thereof. In some embodiments, the diameter dimensions of the first and second

conductive particles

734, 736 can be about 5 microns to 40 microns, such as about 5 microns, 10 microns, 15 microns, 20 microns, 25 microns, 30 microns, 35 microns, or 40 microns.

In some embodiments, the anisotropic conductive film 730 is used in which the insulating adhesive layer 732 is acrylic and has a thickness of about 25 μm. The first and second

conductive particles

734, 736 are polymer microspheres coated with nickel and gold on their surfaces, and have a size of about 20 microns and a density of 300Pcs/mm²。

Referring to fig. 6D, a second electronic component is disposed over the anisotropic conductive film. The second electronic component 740 includes a second substrate 742 and a second conductive element 744 over the second substrate 742. In the vertical direction, the second conductive element 744 overlaps the first conductive element 714 of the first electronic component 710. Specifically, the second conductive element 744 at least partially overlaps the first conductive element 714 at a region vertically projected onto the first substrate 712.

In some embodiments, the second substrate 742 may be a flexible substrate, and the material thereof may include, but is not limited to, polyethylene terephthalate, polyethylene naphthalate, polyethersulfone, polyethylene, polycarbonate, polyimide, or acrylic resin, or the like. In some embodiments, the material of the second conductive element 744 can comprise gold, silver, copper, aluminum, indium tin oxide, composite conductive polymer material, or the like.

Referring to fig. 6E, the elements are pressed together to form the connecting structure 700. The second electronic component 740, the anisotropic conductive film 730, the buffer layer 720, and the first electronic component 710 are pressed, such that the first substrate 712 of the first electronic component 710 and the second substrate 742 of the second electronic component 740 are connected via the insulating glue layer 732, and the first conductive particles 734 between the first conductive element 714 and the second conductive element 744 are compressed and physically contact and electrically connect the first conductive element 714 and the second conductive element 744. During the pressing, the resin in the insulating adhesive layer 732 is hardened by heating, so that the second electronic component 740 is fixed above the first electronic component 710.

At an external vertical pressing force P₁Next, the first conductive particles 734 interposed between the first conductive element 714 and the second conductive element 744 are pressed and deformed, thereby forming an effect of having electrical conduction in the vertical direction under pressure. After the insulating adhesive layer 732 is cured for a period of time, the first conductive particles 734 are no longer moved by the external force to form an electrically conductive structure, thereby electrically connecting the first conductive element 714 and the second conductive element 744. Furthermore, the second conductive particles 736 are located in the region not overlapping the first conductive element 714 and the second conductive element 744 in the vertical direction, and thus are not deformed by being pressed and remain insulated by being surrounded by the insulating adhesive layer 732.

In other embodiments, when the anisotropic conductive film 730 is disposed on the buffer layer 720, a pre-lamination step may be performed to laminate the anisotropic conductive film 730 to the buffer layer 720 and the first electronic component 710 by a lamination device, wherein the pre-lamination temperature may be, for example, about 95 ℃ to 110 ℃. Then, the second electronic component 740 is bonded to the anisotropic conductive film 730, the buffer layer 720, and the first electronic component 710 by a bonding device, wherein the bonding temperature may be, for example, about 160 ℃ to 220 ℃.

Referring to fig. 7A and 7B, enlarged partial views of the connecting structure before and after applying the pressing force are shown. Fig. 7A shows the first conductive particles 734 between the buffer layer 720 and the second conductive element 744 before the lamination. Fig. 7B shows that when the pressing is performed, the height of the first conductive particles 734 is reduced due to the pressing, and the buffer layer 720 is pushed away to contact the first conductive element 714, while the connectivity of the other portion of the anisotropic conductive film 730 is not affected. In one embodiment, the diameter size of the first conductive particles 734 before stitching is 20 microns, the diameter size at the post-stitching level becomes larger to become about 30 microns, and the thickness of the buffer layer 720 is about 2 microns.

Fig. 8 is an alternative embodiment. In this embodiment, the buffer layer 820 of the connection structure 800 is an Organic thin film formed by Organic solder mask (OSP) technology, which is also called an Organic solder mask. The buffer layer 820 includes a first portion 820A in contact with the first substrate 712 and a second portion 820B in contact with the first conductive element 714. Other components of the connection structure 800 are similar to the connection structure 100 discussed above with reference to fig. 1 or the connection structure 700 discussed above with reference to fig. 6A-6E, and thus, will not be described again.

In embodiments where the buffer layer is formed via an organic solderability technique, the material of the first conductive element 714 is copper, and the plated film on the surface of the copper may comprise, for example, rosins, active resins, or azoles. In some embodiments, the organic thin film of an azole may be, for example, Polybenzimidazole (PBI), Benzotriazole (BTA), alkyl Imidazole (IA), Benzimidazole (BIA), Substituted Benzimidazole (SBA), or Alkyl Phenylimidazole (APA). A film of an organic copper complex may be formed on the first conductive element 714 by an organic solderability technique. Since the organic solder mask is easily scratched and broken by high temperature and high pressure during the pressing process, the first conductive particles 734 can be electrically connected to the first conductive elements 714 by exposing the portions of the first conductive elements 714.

Referring to fig. 9, a flow of a method for forming an organic solderability preservative film is shown. In the method 900, first, in step 902, the first conductive element 714 of the first electronic component 710 is degreased. Next, in step 904, a water wash is performed. The copper surface of the first conductive element 714 is then microetched 906. After the microetching, a secondary water wash is performed in step 908. The copper surface of the first conductive element 714 is then microetched 910. Next, in step 912, the first conductive element 714 is rinsed with ultra pure water. Thereafter, in step 914, the OSP solution is brushed on the first electronic component 710 or the first electronic component 710 is dipped in the OSP solution, followed by forming an organic soldermask and air drying. Then, in step 916, the organic solderability mask coated first electronic component 710 is washed with ultra pure water. The cleaned first electronic component 710 is then dried at step 918.

Referring again to fig. 8, the buffer layer 820 is an organic thin film formed by organic solderability preservative, wherein a first portion 820A of the buffer layer 820 contacts the upper surface of the first substrate 712 of the first electronic component 710. The first portion 820A of the buffer layer 820 is an organic thin film including the organic material described above. The second portion 820B of the buffer layer 820 contacts the upper surface and the side surface of the first conductive element 714, and is an organic thin film including a copper complex. In some embodiments, the thickness of the first portion 820A and the second portion 820B of the buffer layer 820 is about 1/20 to about 1/5, preferably about 1/10, of the height of the conductive particles (before lamination) of the anisotropic conductive film, so as to provide a suitable stress buffering effect and enable the first conductive particles 734 to break through the second portion 820B of the buffer layer during lamination.

Fig. 10 shows an alternative embodiment. In this embodiment, the buffer layer 1020 of the connection structure 1000 includes a first portion 1020A in contact with the first substrate 712 and a second portion 1020B in contact with the first conductive element 714. Other components of the connection structure 1000 are similar to the connection structure 100 discussed above with reference to fig. 1 or the connection structure 700 discussed above with reference to fig. 6A-6E, and thus, will not be described again here.

In the connection structure 1000, the second portion 1020B of the buffer layer 1020 is an organic thin film formed by an organic solderability preservative. The first portion 1020A of the buffer layer 1020 is an organic film having a cte between that of the first substrate 712 and that of the insulating glue layer 732, for example, between about 20ppm/K and about 50 ppm/K. The material of the first portion 1020A of the buffer layer 1020 may be, for example, rosins, active resins, azoles, polyetheretherketones, polyimides, acrylics, or the like.

In some embodiments, the method for forming the second portion 1020B of the buffer layer 1020 may be similar to the method 900 for fabricating the organic soldermask described with reference to fig. 9, except that the portion of the first substrate 712 not covered by the first conductive element 714 is covered by a protection layer when the first conductive element 714 is operated; thereafter, after forming the organic solder mask (i.e., the second portion 1020B of the buffer layer 1020) on the upper surface and the side surface of the first conductive element 714, the protective film on the first substrate 712 is removed, and the organic material as described above is disposed on the first substrate 712, for example, by coating, thereby forming the first portion 1020A of the buffer layer 1020.

Fig. 11 is an alternative embodiment. In this embodiment, the upper surface of the first conductive element 714 of the connection structure 1100 is provided with a buffer layer 1120. In some embodiments, the material of the first conductive element 714 is gold, silver, copper, or a combination thereof, and the buffer layer 1120 is a metal plating layer made of zinc, aluminum, lead, cadmium, magnesium, or a combination thereof. Since the thermal expansion coefficient of gold is 14.2, the thermal expansion coefficient of silver is 19.5, and the thermal expansion coefficient of copper is 16.5ppm/K, which are significantly lower than the thermal expansion coefficient of the adhesive insulating layer 732, peeling may easily occur between the adhesive insulating layer 732 and the first conductive member 714. By providing the buffer layer 1120 formed by a metal plating layer on the first conductive element 714, and the thermal expansion coefficient of the metal plating layer is between the thermal expansion coefficient of the first conductive element 714 and the thermal expansion coefficient of the insulating glue layer 732, a function as a buffer layer can be provided, and peeling between the insulating glue layer 732 and the first conductive element 714 can be reduced. Since the electrical function of the device is disabled once the peeling occurs between the adhesive layer 732 and the first conductive element 714, the buffer layer 1120 formed by the metal plating is preferably disposed between the adhesive layer 732 and the first conductive element 714, especially between the adhesive layer 732 and the upper surface of the first conductive element 714. Optionally, the buffer layer may also include a remaining portion, for example, between the insulating glue layer 732 and the side surface of the first conductive element 714, or between the insulating glue layer 732 and the first substrate 712.

In some embodiments, the metallic coating has a coefficient of thermal expansion of about 25ppm/K to about 50ppm/K, such as a coefficient of thermal expansion of 36ppm/K for zinc, a coefficient of thermal expansion of 23.2ppm/K for aluminum, a coefficient of thermal expansion of 29.3ppm/K for lead, a coefficient of thermal expansion of 41.0ppm/K for cadmium, and a coefficient of thermal expansion of 26.0ppm/K for magnesium. In some embodiments, the buffer layer 1120 formed by the metal plating may have a thickness of 5 to 30 μm, but the disclosure is not limited thereto, and the thickness of the metal plating may be adjusted according to the process and process parameters.

As shown in fig. 11, since the electroplating process is anisotropic, the buffer layer 1120 formed by the metal plating is on the upper surface of the first conductive element 714 and contacts the upper surface of the first conductive element 714. Other components of the connection structure 1100 are similar to the connection structure 100 discussed above with reference to fig. 1 or the connection structure 700 discussed above with reference to fig. 6A-6E, and thus, will not be described again here. It should be noted that, in addition to the buffer layer 1120 being disposed on the upper surface of the first conductive element 714, in other practical examples, the buffer layer 1120 may also be disposed on the upper surface of the second conductive element 744, or both the upper surface of the first conductive element 714 and the upper surface of the second conductive element 744 are disposed with the buffer layer 1120. Fig. 12 is an alternative embodiment similar to the connection structure of fig. 11, except that in the connection structure 1200, when the buffer layer 1220 formed by the metal plating layer is formed, the side surface of the first conductive element 714 is also plated with the metal plating layer, so that the buffer layer 1220 formed by the metal plating layer is also used to distribute the stress caused by the difference of the thermal expansion coefficients between the insulating adhesive layer 732 and the side surface of the first conductive element 714.

Fig. 13 is an alternative embodiment, similar to the connection structure of fig. 12, in the connection structure 1300, a first buffer layer 1320 formed by metal plating is disposed between the insulating glue layer 732 and the upper surface and the side surface of the first conductive element 714. The difference between the connection structure 1300 and the connection structure 1200 of fig. 12 is that in the connection structure 1300, the organic thin film is also used as the second buffer layer 1322 between the insulating glue layer 732 and the first substrate 712 to distribute the stress caused by the difference in thermal expansion coefficient.

In some embodiments, after providing the first electronic component 710, a metal plating (i.e., buffer layer 1220), such as zinc, aluminum, lead, cadmium, magnesium, or a combination thereof, is plated over the first conductive element 714. The second buffer layer 1322 formed of the organic thin film may be formed thereafter, for example, by coating. The second buffer layer 1322 has a material having a thermal expansion coefficient between that of the first substrate 712 and that of the insulating glue layer 732, for example, about 25ppm/K to about 50 ppm/K. The material of the second buffer layer 1322 may be, for example, rosin, active resin, azole, polyether ether ketone, polyimide, or acrylic resin.

Fig. 14 is an alternative embodiment. In this embodiment, a first buffer layer 1420 formed by a metal plating layer and a second buffer layer 1422 formed by an organic thin film are disposed on the upper surface and the side surface of the first conductive element 714 of the connection structure 1400, covering the first substrate 712 and the first buffer layer 1420, and the first conductive particles 734 penetrate through the second buffer layer 1422 to electrically connect the first buffer layer 1420 and the first conductive element 714. That is, above the first conductive element 714, the buffer layer may be a composite layer including a first buffer layer 1420 formed by a metal plating layer and a second buffer layer 1422 formed by an organic thin film thereon. Other components of the connection structure 1400 are similar to the connection structure 100 discussed above with reference to fig. 1 or the connection structure 700 discussed above with reference to fig. 6A-6E, and thus, will not be described again.

In some embodiments, after providing the first electronic component 710, a metal plating (i.e., the first buffer layer 1420), such as zinc, aluminum, lead, cadmium, magnesium, or a combination thereof, is plated over the first conductive element 714. The second buffer layer 1422 formed of an organic thin film may be disposed on the first substrate 712 and the first buffer layer 1420 of the first electronic component 710 by, for example, coating or soft-to-hard bonding. In some embodiments, the materials and characteristics of the first buffer layer 1420 and the second buffer layer 1422 may be, for example, the materials and characteristics of the first buffer layer 1320 and the second buffer layer 1322 discussed above with reference to fig. 13.

The connection structure provided by the present disclosure adds a buffer layer having a thermal expansion coefficient between the anisotropic conductive film and the substrate at the interface where the stress and strain concentrates (i.e., the interface between the anisotropic conductive film and the first conductive structure), so as to distribute the stress and strain gradient between the two interfaces (i.e., the conductive element and the buffer layer, the buffer layer and the anisotropic conductive film). Therefore, the problem of the peeling of the anisotropic conductive film caused by the difference of the thermal expansion coefficients is improved. In addition, the position of the buffer layer can be flexibly selected and arranged between interfaces with larger difference of thermal expansion coefficients, such as between the anisotropic conductive film and the substrate.

While the present disclosure has been described with reference to the above embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the disclosure, and therefore the scope of the disclosure should be limited only by the appended claims.

Claims

1. A connecting structure, comprising:

a first electronic component comprising a first substrate and a first conductive element over the first substrate;

a buffer layer disposed on an upper surface of the first conductive element of the first electronic component;

an anisotropic conductive adhesive film comprising an insulating adhesive layer and first conductive particles in the insulating adhesive layer, wherein the insulating adhesive layer is disposed over the first substrate and the first conductive element of the first electronic component and on the buffer layer; and

a second electronic component disposed on the anisotropic conductive film, the second electronic component including a second substrate and a second conductive element under the second substrate, wherein the first conductive particles electrically connect the first conductive element and the second conductive element;

wherein the thermal expansion coefficient of the buffer layer is between that of the first conductive element and that of the insulating glue layer of the anisotropic conductive glue film.

2. The connection structure of claim 1, wherein the buffer layer has a coefficient of thermal expansion of about 20ppm/K to about 50 ppm/K.

3. The connection structure of claim 1, wherein the buffer layer comprises an organic film, a metal plating, or a combination thereof.

4. The connection structure of claim 1, wherein the buffer layer comprises an organic thin film, and the first conductive particles pass through the buffer layer to electrically connect the first conductive elements.

5. The connection structure of claim 1, wherein the anisotropic conductive film further comprises second conductive particles in the insulating glue layer, the second conductive particles do not contact the first conductive element and the second conductive element, and the buffer layer has a thickness of about 1/20 to about 1/5 of a height of the second conductive particles.

6. The connection structure of claim 1, wherein the buffer layer is made of zinc, aluminum, magnesium, lead, cadmium, or a combination thereof.

7. The connection structure of claim 1, wherein the buffer layer is also disposed on a side surface of the first conductive element and over the first substrate.

8. A method of forming a connection structure, comprising:

providing a first electronic component, wherein the first electronic component comprises a first substrate and a first conductive element over the first substrate;

providing a buffer layer on an upper surface of the first conductive element of the first electronic component;

arranging an anisotropic conductive film above the first electronic component and the buffer layer, wherein the anisotropic conductive film comprises an insulating adhesive layer and first conductive particles in the insulating adhesive layer;

arranging a second electronic assembly above the anisotropic conductive adhesive film, wherein the second electronic assembly comprises a second substrate and a second conductive element below the second substrate, and the thermal expansion coefficient of the buffer layer is between the thermal expansion coefficient of the first conductive element and the thermal expansion coefficient of the insulating adhesive layer of the anisotropic conductive adhesive film; and

and laminating the first electronic assembly, the buffer layer, the anisotropic conductive film and the second electronic assembly, wherein the first conductive particles of the anisotropic conductive film are electrically connected with the first conductive element and the second conductive element.

9. The method according to claim 8, wherein the buffer layer comprises an organic film, and the first conductive particles of the anisotropic conductive film penetrate through the organic film to connect the first conductive elements when the first electronic component, the buffer layer, the anisotropic conductive film, and the second electronic component are laminated.

10. The method according to claim 8, wherein the buffer layer comprises a metal plating layer, and the first conductive particles of the anisotropic conductive film electrically connect the first conductive elements by contacting the metal plating layer when the first electronic component, the buffer layer, the anisotropic conductive film, and the second electronic component are bonded.