Low-stress conductive adhesive for electronic packaging and preparation method thereof

Abstract

The invention discloses a low-stress conductive adhesive for electronic packaging and a preparation method thereof, and relates to the technical field of conductive adhesives, and the conductive adhesive comprises the following components in parts by mass: 5-30 parts of bisphenol A epoxy resin, 5-30 parts of a flexibilizer, 5-30 parts of a flexible additive, 50-90 parts of a conductive filler, 10-30 parts of a diluent, 10-30 parts of a curing agent, 1-2 parts of a coupling agent and 1-2 parts of a thixotropic agent. The technical problem that an existing epoxy conductive adhesive is prone to brittle failure due to poor flexibility is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive adhesives, in particular to a low-stress conductive adhesive for electronic packaging and a preparation method thereof. Background Art

[0002] Epoxy conductive adhesive has good conductivity, adhesion, high line resolution, environmental friendliness and good processing performance and is widely used in the field of electronic packaging. At the same time, due to the large brittleness of epoxy conductive adhesive after curing, especially for materials with highly mismatched CTE values, such as alumina ceramics, aluminum alloys and other materials, stress concentration is easily generated at the bonding point due to the mismatch of thermal expansion coefficients under low temperature conditions, which is prone to brittle fracture. Especially for the bonding of large chips or components, cracking is more likely to occur after curing due to excessive stress and poor flexibility, which limits its application range. Summary of the Invention

[0003] The object of the present invention is to provide a low-stress conductive adhesive for electronic packaging and a preparation method thereof in order to solve at least one of the above technical problems.

[0004] In a first aspect, an embodiment of the present invention provides a low-stress conductive adhesive for electronic packaging, which includes, by mass: 5-30 parts of bisphenol A epoxy resin, 5-30 parts of a toughening agent, 5-30 parts of a flexible additive, 50-90 parts of a conductive filler, 10-30 parts of a diluent, 10-30 parts of a curing agent, 1-2 parts of a coupling agent, and 1-2 parts of a thixotropic agent.

[0005] Furthermore, the bisphenol A epoxy resin includes any one or more combinations of the following: bisphenol A epoxy resin, bisphenol F epoxy resin, acrylic epoxy, and novolac epoxy resin.

[0006] Furthermore, the toughening agent includes any one or more combinations of the following: organosilicon-modified epoxy resin, core-shell toughening agent, carboxyl-terminated nitrile rubber, and hydroxyl-terminated polybutadiene.

[0007] Furthermore, the flexible additive includes any one or more combinations of the following: polyether modified epoxy resin, dimer acid modified epoxy resin, aliphatic modified epoxy resin.

[0008] Furthermore, the conductive filler includes any one or more combinations of the following: flake silver powder, bulk silver powder, micron silver powder, and dendritic silver powder.

[0009] Furthermore, the diluent includes any one or more combinations of the following: monofunctional epoxy diluent, difunctional epoxy diluent, trifunctional glycidyl ether, ethylene glycol butyl ether acetate, DBE, and acetone.

[0010] Furthermore, the curing agent includes any one of the following: imidazole latent curing agent, modified amine curing agent, and acid anhydride curing agent.

[0011] Furthermore, the coupling agent includes any one or more combinations of the following: epoxy silane coupling agent, vinyl silane coupling agent, amino silane coupling agent.

[0012] Furthermore, the thixotropic agent includes any one or more combinations of the following: fumed silica, organic bentonite, hydrogenated castor oil, and polyamide wax.

[0013] In a second aspect, an embodiment of the present invention also provides a method for preparing a low-stress conductive adhesive for electronic packaging, comprising: uniformly stirring bisphenol A epoxy resin, a flexible additive, a toughening agent and a diluent in a preset proportion, and vacuum degassing to obtain an initial mixture; wherein the preset proportion is in parts by mass: 5-30 parts of bisphenol A epoxy resin, 5-30 parts of toughening agent, 5-30 parts of flexible additive, 50-90 parts of conductive filler, 10-30 parts of diluent, 10-30 parts of curing agent, 1-2 parts of coupling agent and 1-2 parts of thixotropic agent; adding the curing agent, coupling agent and thixotropic agent to the initial mixture respectively in the preset proportion, and stirring evenly to obtain an organic polymer; adding the conductive filler to the organic polymer in the preset proportion, and mixing evenly to obtain a conductive polymer; grinding, standing, stirring and vacuum degassing the conductive polymer respectively to obtain the low-stress conductive adhesive for electronic packaging.

[0014] The present invention provides a low-stress conductive adhesive for electronic packaging and a preparation method thereof. The conductive adhesive resin matrix has good flexibility and can be uniformly mixed and dispersed with the epoxy resin matrix. At the same time, it is beneficial to the distribution of conductive particles to form a conductive channel, thereby improving the mechanical strength in high and low temperature environments while having good conductor performance, overcoming the defect that existing epoxy conductive adhesives cannot have both flexibility characteristics and high shear strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0016] Figure 1 The present invention provides a flowchart of a method for preparing a low-stress conductive adhesive for electronic packaging. DETAILED DESCRIPTION

[0017] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0018] An embodiment of the present invention provides a low-stress conductive adhesive for electronic packaging, which includes, by mass: 5-30 parts of bisphenol A epoxy resin, 5-30 parts of a toughening agent, 5-30 parts of a flexible additive, 50-90 parts of a conductive filler, 10-30 parts of a diluent, 10-30 parts of a curing agent, 1-2 parts of a coupling agent, and 1-2 parts of a thixotropic agent.

[0019] Preferably, the bisphenol A epoxy resin includes any one or more combinations of the following: bisphenol A epoxy resin, bisphenol F epoxy resin, acrylic epoxy resin, and novolac epoxy resin.

[0020] Preferably, the toughening agent includes any one or more combinations of the following: organosilicon-modified epoxy resin, core-shell toughening agent, carboxyl-terminated nitrile rubber, and hydroxyl-terminated polybutadiene.

[0021] Preferably, the flexible additive comprises any one or more combinations of the following: polyether modified epoxy resin, dimer acid modified epoxy resin, aliphatic modified epoxy resin.

[0022] Preferably, the conductive filler comprises any one or more of the following combinations: flake silver powder, bulk silver powder, micron silver powder, and dendritic silver powder, wherein the size of the micron silver powder is 1 μm-20 μm, and the average particle size is 5 μm-7 μm.

[0023] Preferably, the diluent includes any one or more of the following combinations: monofunctional epoxy diluent, difunctional epoxy diluent, trifunctional glycidyl ether, ethylene glycol butyl ether acetate, dibasic ester (DBE), and acetone.

[0024] Preferably, the curing agent includes any one of the following: imidazole latent curing agent, modified amine curing agent, and acid anhydride curing agent.

[0025] Preferably, the coupling agent includes any one or more combinations of the following: epoxy silane coupling agent, vinyl silane coupling agent, amino silane coupling agent.

[0026] Preferably, the thixotropic agent comprises any one or more combinations of the following: fumed silica, organic bentonite, hydrogenated castor oil, and polyamide wax.

[0027] Figure 1 FIG. 1 is a flow chart of a method for preparing a low stress conductive adhesive for electronic packaging according to an embodiment of the present invention. Figure 1 As shown, the method specifically includes the following steps:

[0028] Step S102, bisphenol A epoxy resin, flexible additive, toughening agent and diluent are stirred evenly in a preset proportion, and vacuum degassing is performed to obtain an initial mixture; wherein the preset proportion is based on mass: bisphenol A epoxy resin 5-30 parts, toughening agent 5-30 parts, flexible additive 5-30 parts, conductive filler 50-90 parts, diluent 10-30 parts, curing agent 10-30 parts, coupling agent 1-2 parts and thixotropic agent 1-2 parts.

[0029] Preferably, the vacuum degassing time is 3 min to 5 min.

[0030] Step S104 , adding a curing agent, a coupling agent, and a thixotropic agent to the initial mixture according to a preset ratio, and stirring the mixture to obtain an organic polymer.

[0031] Step S106 , adding the conductive filler into the organic polymer according to a preset ratio, and mixing them evenly to obtain the conductive polymer.

[0032] Step S108 , grinding, standing, stirring, and vacuum degassing the conductive polymer to obtain a low-stress conductive adhesive for electronic packaging.

[0033] Specifically, the three-roll mill is first used to grind the adhesive under appropriate roller gap to obtain a suitable fineness; then, after standing for 5 minutes, stirring and vacuum degassing are performed for 5 minutes to 10 minutes to obtain a low-stress conductive adhesive for electronic packaging.

[0034] Example 1

[0035] An embodiment of the present invention provides a low-stress conductive adhesive for electronic packaging, comprising, by weight:

[0036] Organic polymer: 25 parts; micron silver powder as conductive filler: 75 parts.

[0037] The organic polymer comprises a resin matrix and other additives, wherein the resin matrix is ​​composed of 10 parts by mass of bisphenol A epoxy resin, 30 parts by mass of organosilicon-modified epoxy resin, and 10 parts by mass of a flexible additive;

[0038] Other additives are calculated by weight as follows: 30 parts of diluent, 17 parts of curing agent, 1 part of thixotropic agent, and 2 parts of coupling agent. The coupling agent is one or a combination of epoxy silane coupling agent, vinyl silane coupling agent, and amino silane coupling agent.

[0039] The prepared organic polymer and micron silver are mixed evenly, and then subjected to three-roller grinding and planetary degassing to obtain a low-stress conductive adhesive for electronic packaging.

[0040] The prepared low-stress conductive adhesive is then cured at 100° C. for 1 hour.

[0041] After curing, the samples were tested for volume resistivity, die shear strength and thermal conductivity.

[0042] Example 2

[0043] Same as Example 1, except that the amount of the flexible additive is 5 parts.

[0044] Example 3

[0045] Same as Example 1, except that the amount of the flexible additive is 20 parts.

[0046] Example 4

[0047] Same as Example 1, except that the amount of the flexible additive is 30 parts.

[0048] Example 5

[0049] Same as Example 1, except that the added amount of bisphenol A epoxy resin is 5 parts.

[0050] Example 6

[0051] Same as Example 1, except that the added amount of bisphenol A epoxy resin is 20 parts.

[0052] Example 7

[0053] Same as Example 1, except that the added amount of bisphenol A epoxy resin is 30 parts.

[0054] Example 8

[0055] Same as Example 1, except that the amount of modified epoxy resin added is 5 parts.

[0056] Example 9

[0057] Same as Example 1, except that the amount of modified epoxy resin added is 10 parts.

[0058] Example 10

[0059] Same as Example 1, except that the amount of modified epoxy resin added is 20 parts.

[0060] Example 11

[0061] Same as Example 1, except that the conductive filler is bulk silver powder.

[0062] Example 12

[0063] Same as Example 1, except that the amount of micron silver powder added is 70 parts.

[0064] Example 13

[0065] Same as Example 12, except that the conductive filler is bulk silver powder.

[0066] Example 14

[0067] Same as Example 1, except that the amount of micron silver powder added is 80 parts.

[0068] Example 15

[0069] Same as Example 14, except that the conductive filler is bulk silver powder.

[0070] Example 16

[0071] Same as Example 1, except that the amount of micron silver powder added is 90 parts.

[0072] Example 17

[0073] Same as Example 16, except that the conductive filler is bulk silver powder.

[0074] Example 18

[0075] Same as Example 1, except that the amount of curing agent added is 10 parts.

[0076] Example 19

[0077] Same as Example 1, except that the amount of curing agent added is 20 parts.

[0078] Example 20

[0079] Same as Example 1, the amount of diluent added is 30 parts.

[0080] The performance tests were performed on the low-stress conductive adhesives in the above embodiments:

[0081] Volume resistivity: The prepared low-stress conductive adhesive was coated on a glass substrate to form a conductive adhesive film with a length of 8.5 cm and a width of 1 cm. After curing, the volume resistivity was tested using a four-probe resistance tester.

[0082] Chip shear strength: A 2mm×2mm silicon-based chip was bonded to a gold-plated Kovar substrate using the prepared low-stress conductive adhesive. After curing, the chip shear strength (kgf) was tested using a thrust tester.

[0083] Thermal conductivity: The solidified sample was made into a small flat disc with a diameter of about 12.7 mm and a thickness of about 2 mm. Graphite was evenly sprayed on the surface of the sample. The thermal diffusivity of the sample was measured with a laser thermal conductivity meter, the specific heat capacity of the sample was measured with a differential scanning calorimeter, and the density of the sample was measured with a densitometer. The thermal conductivity of the sample was obtained by calculation (thermal conductivity = thermal diffusivity × specific heat capacity × density).

[0084] Temperature shock test: The prepared chip shear samples were placed in a temperature shock test chamber. The test temperature range was -65-150°C, with 100 cycles, a dwell time of 20 minutes, and a switching time of no more than 1 minute. The characterization results of each example are shown in Table 1:

[0085] Table 1

[0086]

[0087]

[0088] From the above description, it can be seen that the embodiment of the present invention provides a low-stress conductive adhesive for electronic packaging and a preparation method thereof. The curing process is simple and can be cured in 10 minutes at 100°C. The low-stress conductive adhesive is a single component, has good operating performance, is easy to use, is suitable for dispensing with automated equipment, has a simple preparation process, and is conducive to mass production.

[0089] Furthermore, the present invention improves the brittleness of the resin and the flexibility of the conductive adhesive after curing by adding a macromolecular structure containing a flexible chain segment as a flexible additive. At the same time, it has good mechanical properties and high and low temperature resistance, thereby improving environmental reliability.

[0090] The volume resistivity of the low stress conductive adhesive provided by the embodiment of the present invention is better than 4.0×10 -4 , and has good thermal conductivity, can be used in but not limited to surface mounting of chips, components, packaging of semiconductor integrated circuits, LED packaging, structural fixation and other electronic packaging fields.

[0091] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0092] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A low stress conductive adhesive for electronic packaging, characterized in that: The composition comprises, by mass, 5-30 parts of bisphenol A epoxy resin, 5-30 parts of toughening agent, 5-30 parts of flexible additive, 50-90 parts of conductive filler, 10-30 parts of diluent, 10-30 parts of curing agent, 1-2 parts of coupling agent and 1-2 parts of thixotropic agent.

2. The low-stress conductive adhesive for electronic packaging according to claim 1, wherein: The bisphenol A epoxy resin includes any one or more of the following combinations: bisphenol A epoxy resin, bisphenol F epoxy resin, acrylic epoxy resin, and novolac epoxy resin.

3. The low-stress conductive adhesive for electronic packaging according to claim 1, wherein: The toughening agent includes any one or more combinations of the following: organosilicon-modified epoxy resin, core-shell toughening agent, carboxyl-terminated nitrile rubber, and hydroxyl-terminated polybutadiene.

4. The low-stress conductive adhesive for electronic packaging according to claim 1, wherein: The flexible additive comprises any one or more combinations of the following: polyether modified epoxy resin, dimer acid modified epoxy resin, aliphatic modified epoxy resin.

5. The low-stress conductive adhesive for electronic packaging according to claim 1, wherein: The conductive filler includes any one or more combinations of the following: flaky silver powder, bulk silver powder, micron silver powder, and dendritic silver powder.

6. The low-stress conductive adhesive for electronic packaging according to claim 1, wherein: The diluent includes any one or more combinations of the following: monofunctional epoxy diluent, difunctional epoxy diluent, trifunctional glycidyl ether, ethylene glycol butyl ether acetate, DBE, and acetone.

7. The low-stress conductive adhesive for electronic packaging according to claim 1, wherein: The curing agent includes any one of the following: imidazole latent curing agent, modified amine curing agent, and acid anhydride curing agent.

8. The low-stress conductive adhesive for electronic packaging according to claim 1, wherein: The coupling agent includes any one or more combinations of the following: epoxy silane coupling agent, vinyl silane coupling agent, and amino silane coupling agent.

9. The low-stress conductive adhesive for electronic packaging according to claim 1, wherein: The thixotropic agent includes any one or more combinations of the following: fumed silica, organic bentonite, hydrogenated castor oil, and polyamide wax.

10. A method for preparing the low-stress conductive adhesive for electronic packaging according to any one of claims 1 to 9, characterized in that: include: Bisphenol A epoxy resin, a flexible additive, a toughening agent, and a diluent are uniformly stirred in a preset proportion, and vacuum degassing is performed to obtain an initial mixture; wherein the preset proportion is, in parts by mass: 5-30 parts of bisphenol A epoxy resin, 5-30 parts of toughening agent, 5-30 parts of flexible additive, 50-90 parts of conductive filler, 10-30 parts of diluent, 10-30 parts of curing agent, 1-2 parts of coupling agent, and 1-2 parts of thixotropic agent; Adding a curing agent, a coupling agent and a thixotropic agent to the initial mixture respectively according to the preset proportions, and stirring uniformly to obtain an organic polymer; Adding the conductive filler to the organic polymer according to the preset ratio and mixing them evenly to obtain a conductive polymer; The conductive polymer is ground, allowed to stand, stirred and vacuumed for degassing to obtain the low-stress conductive adhesive for electronic packaging.

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