Thin film circuit with gold-tin pre-pad having a buffer structure and method of manufacturing the same

Abstract

The application discloses a thin film circuit with a gold-tin preformed pad with a buffer structure and a preparation method thereof, and relates to the technical field of thin film circuits. The thin film circuit comprises a thin film circuit substrate, a functional layer arranged on the thin film circuit substrate, a metal buffer layer arranged on the functional layer, and a gold-tin preformed pad arranged on the metal buffer layer. The highest melting point of the metal buffer layer is lower than the lowest melting point of the gold-tin preformed pad, and the gold-tin preformed pad is prepared from gold-tin eutectic solder. During the heating process of the thin film circuit, when the heating temperature is lower than the lowest melting point of the gold-tin preformed pad and higher than the highest melting point of the metal buffer layer, the metal buffer layer is melted into a liquid metal, thereby reducing the stress between the gold-tin preformed pad and the functional layer and improving the welding reliability.

Description

Technical Field

[0001] This invention relates to the field of thin-film circuit technology, and in particular to a thin-film circuit with a buffer structure gold-tin preformed pad and its fabrication method. Background Technology

[0002] Thin-film circuits refer to circuit elements fabricated by integrating passive components, such as resistors, inductors, and capacitors, onto a circuit substrate using thin-film processes such as evaporation, sputtering, photolithography, electroplating, and etching. Compared to thick-film circuits, thin-film circuits offer advantages such as a wider range of component parameters, higher precision, better temperature and frequency characteristics, higher integration density, and smaller size. Therefore, the use of thin-film circuits is increasing. In the packaging process of thin-film circuits, gold-tin eutectic solder AuSn20 (80-20 wt%) is widely used. When the weight ratio of gold to tin is 80:20 (i.e., AuSn20), it is located in the Au-Sn eutectic region, with a melting point of 280℃. At this temperature, even a small overheating is sufficient to melt and wet the alloy. In practical applications, the gold-tin ratio in gold-tin eutectic solder ranges from 70:30 to 80:20. Because gold-tin eutectic solder has a moderate welding temperature, high yield strength, no need for flux, good wettability, low viscosity, high corrosion resistance, high creep resistance, and good thermal and electrical conductivity, it is widely used in the welding and packaging of optoelectronic devices in fields such as communications, satellites, remote sensing, radar, automobiles, and aerospace.

[0003] However, gold-tin eutectic solder is a high-temperature solder with a minimum soldering temperature of 280°C. The solder must be heated to above 280°C to melt. Before reaching 280°C, the solder expands due to heat, resulting in significant stress between the gold-tin eutectic solder and the thin-film circuit. This can have unpredictable adverse effects on the soldered thin-film circuit. Summary of the Invention

[0004] The purpose of this invention is to provide a thin film circuit with a gold-tin preformed pad having a buffer structure and a method for its fabrication, which reduces the stress between the gold-tin preformed pad and the underlying thin film circuit and improves the welding reliability.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] The present invention provides a thin film circuit with gold-tin preformed pads having a buffer structure, comprising: a thin film circuit substrate, a functional layer disposed on the thin film circuit substrate, a metal buffer layer disposed on the functional layer, and gold-tin preformed pads disposed on the metal buffer layer;

[0007] The highest melting point of the metal buffer layer is lower than the lowest melting point of the gold-tin preformed pad, and the gold-tin preformed pad is made of gold-tin eutectic solder;

[0008] During the heating process of the thin-film circuit, when the heating temperature is lower than the lowest melting point of the gold-tin preformed pads but higher than the highest melting point of the metal buffer layer, the metal buffer layer melts into liquid metal; the liquid metal is used to reduce the stress between the gold-tin preformed pads and the functional layer.

[0009] Optionally, the thickness of the metal buffer layer is 0.1 μm to 1.0 μm.

[0010] Optionally, the thickness of the gold-tin preformed pad is 2μm to 100μm.

[0011] Optionally, the melting point range of the gold-tin preformed pad is 280℃~320℃; the maximum melting point of the metal buffer layer is below 280℃.

[0012] Optionally, the metal buffer layer is made of a mixed metal material; the mixed metal material is an indium-tin material with a ratio of 50:50, an indium-lead material with a ratio of 70:30, a tin-silver material with a ratio of 96:4, or a tin-lead-silver material with a ratio of 10:88:2.

[0013] Optionally, the functional layer is fabricated from thin-film circuit microstrip lines.

[0014] Optionally, the thin-film circuit substrate is a ceramic substrate.

[0015] The present invention also provides a method for fabricating a thin-film circuit with a gold-tin preformed pad having a buffer structure, comprising:

[0016] Deposit the functional layers required for thin-film circuits on the surface of a thin-film circuit substrate;

[0017] Thin-film circuit patterns are fabricated on the functional layer;

[0018] Windows for fabricating gold-tin preformed pads are fabricated on the thin-film circuit pattern;

[0019] A metal buffer layer is prepared on the window;

[0020] Gold-tin preformed pads are prepared on the metal buffer layer;

[0021] The highest melting point of the metal buffer layer is lower than the lowest melting point of the gold-tin preformed pad, and the gold-tin preformed pad is made of gold-tin eutectic solder.

[0022] Optionally, the step of processing a window on the thin-film circuit pattern for fabricating gold-tin preformed pads specifically includes:

[0023] Photoresist is applied to the thin-film circuit pattern by spin coating or spray coating, and windows for preparing gold-tin preformed pads are processed by exposure and development.

[0024] Optionally, after preparing the gold-tin preformed pads on the metal buffer layer, the method further includes:

[0025] Clean the photoresist and cut the thin film circuit according to the thin film circuit pattern to obtain the thin film circuit.

[0026] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0027] A metal buffer layer with a maximum melting point lower than the minimum melting point of the gold-tin preformed pad is designed and fabricated between the gold-tin preformed pad and the underlying thin-film circuit (i.e., functional layer). When the heating temperature is lower than the minimum melting point of the gold-tin preformed pad but higher than the maximum melting point of the metal buffer layer, the metal buffer layer melts first and forms a small amount of liquid metal, which reduces the stress between the gold-tin preformed pad and the underlying thin-film circuit and improves the welding reliability.

[0028] In addition, the gold-tin preformed pads made from gold-tin eutectic solder have high positioning accuracy, are easy to weld thin film circuits, are strong and reliable. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the thin-film circuit with a buffer structure gold-tin preformed pad according to the present invention.

[0031] Figure 2 This is a schematic flowchart illustrating the fabrication method of the thin-film circuit with a buffer structure gold-tin preformed pad according to the present invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] Example 1

[0035] This invention provides a thin-film integrated circuit (hereinafter referred to as thin-film circuit). The thin-film circuit has a gold-tin preformed eutectic pad with a thickness of 2 to 100 μm and a melting point between 280 and 320°C fabricated at a designated location. A metal buffer layer with a melting point below 280°C and a thickness ranging from 0.1 to 1.0 μm is fabricated between the gold-tin preformed pad and the surface of the thin-film circuit.

[0036] like Figure 1 As shown in the figure, a thin film circuit with a buffer structure gold-tin preformed pad provided in this embodiment of the invention includes: a thin film circuit substrate 1, a functional layer 2 disposed on the thin film circuit substrate 1, a metal buffer layer 3 disposed on the functional layer 2, and a gold-tin preformed pad 4 disposed on the metal buffer layer 3; the highest melting point of the metal buffer layer 3 is lower than the lowest melting point of the gold-tin preformed pad 4, and the gold-tin preformed pad 4 is made of gold-tin eutectic solder;

[0037] During the heating process of the thin-film circuit, when the heating temperature is lower than the lowest melting point of the gold-tin preformed pad 4 and higher than the highest melting point of the metal buffer layer 3, the metal buffer layer 3 melts into liquid metal; the liquid metal is used to reduce the stress between the gold-tin preformed pad 4 and the functional layer 2.

[0038] The thickness of the metal buffer layer 3 is 0.1 μm to 1.0 μm. The thickness of the gold-tin preformed pad 4 is 2 μm to 100 μm.

[0039] The melting point range of the gold-tin preformed solder pad 4 is 280℃~320℃; the maximum melting point of the metal buffer layer 3 is below 280℃.

[0040] The metal buffer layer 3 is made of a mixed metal material; the mixed metal material is an indium-tin material with a ratio of 50:50, an indium-lead material with a ratio of 70:30, a tin-silver material with a ratio of 96:4, or a tin-lead-silver material with a ratio of 10:88:2.

[0041] The functional layer 2 is fabricated from thin-film circuit microstrip lines.

[0042] The thin-film circuit substrate 1 is a ceramic substrate.

[0043] Example 2

[0044] This invention provides a method for fabricating a thin-film circuit with a buffered gold-tin preformed pad as described in Embodiment 1. The main steps are as follows:

[0045] Step 100: Deposit the functional layer required for the thin film circuit on the surface of the thin film circuit substrate.

[0046] Preferably, the thin-film circuit substrate is a ceramic substrate; the functional layer is a thin-film circuit microstrip line.

[0047] Step 200: Fabricate a thin-film circuit pattern on the functional layer, specifically as follows:

[0048] Thin-film circuit patterns are fabricated on the functional layer using processes such as photolithography and etching.

[0049] Step 300: A window for fabricating gold-tin preformed pads is fabricated on the thin-film circuit pattern; specifically:

[0050] Photoresist is applied to the thin-film circuit pattern by spin coating or spray coating, and windows for preparing gold-tin preformed pads are processed by exposure and development.

[0051] Step 400: Prepare a metal buffer layer on the window, specifically as follows:

[0052] A metal buffer layer is prepared on the window using processes such as vacuum coating, evaporation, or electroplating.

[0053] Step 500: Prepare gold-tin preformed pads on the metal buffer layer, specifically as follows:

[0054] Gold-tin preformed pads are prepared on the metal buffer layer using processes such as vacuum coating, evaporation, or electroplating.

[0055] The highest melting point of the metal buffer layer is lower than the lowest melting point of the gold-tin preformed pad.

[0056] The thickness of the gold-tin preformed pad is 2 to 100 μm. The gold-tin preformed pad is made of gold-tin eutectic solder. The ratio of gold to tin in the gold-tin preformed pad is in the range of 70:30 to 80:20.

[0057] The highest melting point of the metal buffer layer is below 280°C, and the metal buffer layer includes, but is not limited to, indium tin (50:50), indium lead (70:30), tin silver (96:4), tin lead silver (10:88:2), etc.

[0058] Furthermore, the preparation method also includes:

[0059] The photoresist and / or solder on the photoresist are cleaned off, and the thin film circuit is obtained by cutting according to the circuit pattern. The thin film circuit is used to fabricate gold-tin preformed pads with a buffer structure.

[0060] This invention provides a thin-film circuit with a buffer structure and a method for fabricating the same. The window requiring the gold-tin preformed pad is prepared by photoresist coating and photolithography. Then, a metal buffer layer with a thickness of 0.1–1.0 μm is first prepared on the window by vacuum deposition or electroplating. The metal buffer layer has a melting point below 280°C and includes, but is not limited to, indium tin (50:50), indium lead (70:30), tin silver (96:4), and tin lead silver (10:88:2). Next, a gold-tin layer with a thickness of 2–100 μm (gold to tin ratio ranging from 70:30 to 80:20) is prepared on the metal buffer layer by vacuum deposition or electroplating. Finally, the photoresist is peeled off to form the gold-tin preformed pad with the buffer structure. Before the gold-tin preformed pads are heated to 280°C, and after the temperature reaches the melting temperature of the metal buffer layer, the metal buffer layer melts first, forming a small amount of liquid. This reduces the stress between the gold-tin preformed pads and the underlying thin-film circuit (i.e., the functional layer), and improves the welding reliability.

[0061] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0062] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A thin-film circuit with gold-tin preformed pads having a buffer structure, characterized in that, include: A thin-film circuit substrate, a functional layer disposed on the thin-film circuit substrate, a metal buffer layer disposed on the functional layer, and gold-tin preformed pads disposed on the metal buffer layer; The highest melting point of the metal buffer layer is lower than the lowest melting point of the gold-tin preformed pad, and the gold-tin preformed pad is made of gold-tin eutectic solder; During the heating process of the thin-film circuit, when the heating temperature is lower than the lowest melting point of the gold-tin preformed pads but higher than the highest melting point of the metal buffer layer, the metal buffer layer melts into liquid metal; the liquid metal is used to reduce the stress between the gold-tin preformed pads and the functional layer. The melting point range of the gold-tin preformed pad is 280℃~320℃; the maximum melting point of the metal buffer layer is below 280℃.

2. The thin-film circuit with a buffered gold-tin preformed pad according to claim 1, characterized in that, The thickness of the metal buffer layer is 0.1 μm to 1.0 μm.

3. A thin-film circuit with a buffered gold-tin preformed pad according to claim 1, characterized in that, The thickness of the gold-tin preformed pad is 2μm to 100μm.

4. A thin-film circuit with a buffered gold-tin preformed pad according to claim 1, characterized in that, The metal buffer layer is made of a mixed metal material; the mixed metal material is an indium-tin material with a ratio of 50:50, an indium-lead material with a ratio of 70:30, a tin-silver material with a ratio of 96:4, or a tin-lead-silver material with a ratio of 10:88:

2.

5. A thin-film circuit with a buffered gold-tin preformed pad according to claim 1, characterized in that, The functional layer is fabricated from thin-film circuit microstrip lines.

6. A thin-film circuit with a buffered gold-tin preformed pad according to claim 1, characterized in that, The thin-film circuit substrate is a ceramic substrate.

7. A method for fabricating a thin-film circuit with gold-tin preformed pads having a buffer structure, characterized in that, include: Deposit the functional layers required for thin-film circuits on the surface of a thin-film circuit substrate; Thin-film circuit patterns are fabricated on the functional layer; Windows for fabricating gold-tin preformed pads are fabricated on the thin-film circuit pattern; A metal buffer layer is prepared on the window; Gold-tin preformed pads are prepared on the metal buffer layer; Wherein, the highest melting point of the metal buffer layer is lower than the lowest melting point of the gold-tin preformed pad, and the gold-tin preformed pad is made of gold-tin eutectic solder; The melting point range of the gold-tin preformed pad is 280℃~320℃; the maximum melting point of the metal buffer layer is below 280℃.

8. The method for fabricating a thin-film circuit with a buffered gold-tin preformed pad according to claim 7, characterized in that, The process of fabricating a window for preparing a gold-tin preformed pad on the thin-film circuit pattern specifically includes: Photoresist is applied to the thin-film circuit pattern by spin coating or spray coating, and windows for preparing gold-tin preformed pads are processed by exposure and development.

9. The method for fabricating a thin-film circuit with a buffered gold-tin preformed pad according to claim 8, characterized in that, After preparing the gold-tin preformed pads on the metal buffer layer, the process further includes: Clean the photoresist and cut the thin film circuit according to the thin film circuit pattern to obtain the thin film circuit.

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