Film layer design and preparation method of surface acoustic wave device

Abstract

The invention relates to the technical field of SAW (Surface Acoustic Wave) electronic devices, in particular to a film layer design and preparation method of a surface acoustic wave device, comprising a substrate, a WALL PI layer and a ROOF PI layer from bottom to top; a PAD structure is arranged between the substrate and the WALL PI layer; the PAD structure is in contact with the substrate; the WALL PI layer and the ROOF PI layer are provided with a through hole above the PAD structure, the side wall and the bottom of the through hole are covered with a UBM layer, and the UBM layer is in contact with the PAD structure; solder balls are arranged on the surface of the UBM layer, and the UBM layer and the solder balls are electrically communicated through electroplating filling copper. According to the invention, a special structure is arranged on the surface of the original PAD layer, the contact area between the UBM layer and the PAD layer is increased, and the bonding force between the film layers is improved, so that the bonding strength between the film layers is improved, and the reliability of the surface acoustic wave device is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of SAW surface acoustic wave electronic devices, and in particular to a film layer design of a surface acoustic wave device and a preparation method thereof. Background Art

[0002] Surface acoustic wave (SAW) filter is an important radio frequency device, widely used in communication devices such as smart phones, wireless communication base stations and Internet of Things devices. Surface acoustic wave filter is designed based on the characteristics of sound wave propagation on the solid surface, and a specific electrode structure is designed to achieve selective filtering of specific frequency signals. With the rapid development of communication technology, the requirements for miniaturization, high frequency and high reliability of SAW filters are gradually increasing, which in turn puts forward higher requirements for SAW filter packaging technology, requiring its electrical performance to remain stable and reliable in various complex environments (such as high temperature, high humidity, vibration).

[0003] In such Figure 1 In the existing SAW filter WLP packaging structure shown in the figure, the UBM (Under Bump Metal) layer and the PAD layer on the chip surface are very easy to fall off, resulting in reliability failure problems. The UBM layer is an important metal layer between the chip solder ball (bump) and the substrate. It is usually composed of a multi-layer metal structure and plays a key role in the reliability of the entire device. However, in long-term use, this position is also the most prone to failure. This is because the UBM layer is located between the piezoelectric layer (i.e. Figure 1 The interconnection interface between the electrode pad layer and the electroplated bump layer on the surface of the piezoelectric substrate is easily damaged by thermal cycling and thermal expansion mismatch (the difference in thermal expansion coefficients between the packaging material and the piezoelectric substrate during high and low temperature processes leads to thermal stress accumulation), mechanical fatigue (mechanical vibration and impact may cause packaging material fatigue) or moisture intrusion (in a high humidity environment, sealing defects lead to water vapor entering and causing electrode corrosion), which may cause film delamination or shedding, resulting in degradation of electrical performance or even failure, seriously affecting the device life.

[0004] To improve the reliability of the UBM layer, the following measures have been proposed:

[0005] 1) Pre-cleaning: Before the UBM layer is deposited, the underlying material (i.e., the Pad layer material), such as aluminum or low-k dielectric, is properly pre-treated to remove oxides or contaminants and enhance adhesion. Plasma technology is usually used to activate the surface and the UBM layer is quickly deposited in a vacuum environment to avoid contamination and thus improve adhesion.

[0006] 2) Select appropriate interface materials: The structure and material of the UBM layer will affect its adhesion to the underlying material. For this reason, an additional adhesion layer (such as Ti, W or Cr) can be added between the UBM layer and the underlying material, thereby significantly improving the interface bonding strength.

[0007] 3) Optimize PVD deposition process parameters: for example, by increasing the deposition temperature to enhance the diffusion and bonding between the UBM layer and the underlying material; by optimizing the deposition rate to form a denser and more uniform UBM layer; post-deposition annealing treatment can promote atomic diffusion between the UBM layer metal and the underlying material and enhance interface bonding.

[0008] 4) Interface chemical reaction control: Interface chemical reactions (such as the formation of intermetallic compounds) can increase or weaken the adhesion between the UBM layer and the underlying layer. The risk of excessive chemical reactions can be reduced by optimizing the alloy composition and adjusting the composition of the UBM or Pad layer material (such as increasing or decreasing the Cu content), thereby improving interface adhesion.

[0009] 5) Optimize the thickness of the UBM layer: The thickness of the UBM layer has an important impact on the electromigration (EM) failure mode. An excessively thick UBM layer may lead to reduced electromigration resistance, while optimizing the thickness can significantly extend the service life.

[0010] The above methods basically improve the reliability of the UBM layer from the perspective of packaging technology and bonding surface materials, but the process is relatively complicated, difficult to operate, and will increase additional costs. In addition, the prior art does not improve the UBM layer structure itself. Summary of the invention

[0011] In order to solve the above problems, the present invention provides a membrane layer design of a surface acoustic wave device and a preparation method thereof, comprising the following steps:

[0012] S1. A filter pattern is formed on the surface of the substrate to obtain a PAD layer according to a microelectronic process; and then a bonding film layer is formed on the surface of the PAD layer;

[0013] S2. A WALL PI layer is fabricated on the surface of the substrate and the surface of the PAD layer according to the microelectronics process; and a ROOF PI layer is fabricated on the surface of the WALL PI layer;

[0014] S3. Use PVD process to plate UBM layer on the side wall of WALL PI layer, the side wall of ROOF PI layer, the exposed surface of PAD layer, and the exposed surface of bonding film layer;

[0015] S4. WLP packaging is completed using electroplating process and solder ball printing process.

[0016] Furthermore, step S1 of making a bonding film layer on the surface of the PAD layer is to make a plurality of raised PAD bonding blocks on the surface of the PAD layer; when making the UBM layer, each PAD block is completely covered by the UBM layer material.

[0017] Furthermore, all PAD combination blocks are arranged at equal intervals in a matrix form.

[0018] Furthermore, the angle between the side surface of the PAD combining block and the upper surface of the PAD layer is between 0° and 180°.

[0019] Furthermore, step S1 of making a bonding film layer on the surface of the PAD layer is to make a groove in the PAD layer; when making the UBM layer, the groove is completely filled with the UBM layer material.

[0020] Furthermore, the angle between the groove side surface and the groove bottom surface is between 0° and 180°.

[0021] Beneficial effects of the present invention:

[0022] The surface acoustic wave filter WLP packaging structure proposed by the present invention sets a special structure on the original PAD layer surface to increase the contact area between the UBM layer and the PAD layer, improve the bonding force between the film layers, and then increase the bonding strength between the film layers, effectively improving the reliability of the surface acoustic wave device. The preparation process used in this structure is easy to implement and easy to promote on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the existing structure;

[0024] Figure 2 This is a diagram of a WLP package structure of a surface acoustic wave filter according to an embodiment of the present invention;

[0025] Figure 3 This is a structural diagram of a surface acoustic wave filter WLP package according to another embodiment of the present invention;

[0026] Figure 4 It is a schematic diagram of the PAD structure of the present invention;

[0027] Figure 5 A schematic diagram of the structure preparation process of another embodiment of the present invention;

[0028] Among them, 1-substrate, 2-WALL PI layer, 3-ROOF PI layer, 4-PAD layer, 41-PAD binding block, 42-groove, 5-UBM layer, 6-tin ball. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The present invention provides a membrane layer design of a surface acoustic wave device and a preparation method thereof, comprising the following steps:

[0031] S1. A filter pattern is formed on the surface of the substrate to obtain a PAD layer according to a microelectronic process; and then a bonding film layer is formed on the surface of the PAD layer;

[0032] S2. A WALL PI layer is fabricated on the surface of the substrate and the surface of the PAD layer according to the microelectronics process; and a ROOF PI layer is fabricated on the surface of the WALL PI layer;

[0033] S3. Use PVD process to plate UBM layer on the side wall of WALL PI layer, the side wall of ROOF PI layer, the exposed surface of PAD layer, and the exposed surface of bonding film layer;

[0034] S4. WLP packaging is completed using electroplating process and solder ball printing process.

[0035] Specifically, Figure 2 , Figure 3 As shown, the surface acoustic wave filter WLP packaging structure manufactured according to the method of the present invention includes a substrate, a WALL PI layer and a ROOF PI layer from bottom to top;

[0036] A PAD structure is provided between the substrate and the WALL PI layer; the PAD structure is in contact with the substrate;

[0037] The WALL PI layer and the ROOF PI layer have through holes above the PAD structure, and the sidewalls and bottom of the through holes are covered with a UBM layer, and the UBM layer is in contact with the PAD structure; solder balls are provided on the surface of the UBM layer, and electrical connection is achieved between the UBM layer and the solder balls by electroplating copper filling.

[0038] In one embodiment, if Figure 3 As shown, the PAD structure includes a PAD layer, and a groove is provided in the PAD layer. The groove is an arc-shaped groove with a certain curvature. In this embodiment, a plurality of arc-shaped grooves are provided in the PAD layer, and the arc lengths of these arc-shaped grooves are not necessarily the same, but the cross-sectional shapes are the same, and all the arc-shaped grooves correspond to the same center of a circle. In this embodiment, when making the PAD structure, a PAD layer is first made on the surface of the substrate, and then a plurality of concentric rings of different sizes are designed on the plane where the surface of the PAD layer is located, and arc-shaped grooves are opened at the positions of the PAD layer corresponding to the concentric rings, such as Figure 4 shown.

[0039] The angle between the groove side surface and the groove bottom surface is between 0° and 180°.

[0040] In one embodiment, the PAD structure includes a PAD layer, in which a plurality of grooves are arranged in an array at equal intervals, and the angle between the side surface of the groove and the bottom surface of the groove is between 0° and 180°.

[0041] In one embodiment, if Figure 2 As shown, the PAD structure includes a PAD layer and a PAD combining block protruding from the upper surface of the PAD layer.

[0042] Specifically, a plurality of identical PAD binding blocks are protruded from the upper surface of the PAD layer, and all the PAD binding blocks are arranged at equal intervals in a matrix array, such as Figure 4 shown.

[0043] Specifically, a plurality of identical PAD combining blocks are protruded from the upper surface of the PAD layer, and all the PAD combining blocks can form a plurality of circular rings around a center of a circle.

[0044] Specifically, the angle between the side surface of the PAD combining block and the upper surface of the PAD layer is between 0° and 180°.

[0045] Specifically, in the present embodiment, the PAD block is designed to be cylindrical or truncated cone-shaped; specifically, when the angle is between 90° and 180°, the PAD combining block is truncated cone-shaped; when the angle is 90°, the PAD combining block is cylindrical; when the angle is between 0° and 90°, the PAD combining block is inverted truncated cone-shaped.

[0046] Specifically, a bonding film layer is formed on the surface of the PAD layer to form a plurality of protruding PAD bonding blocks on the surface of the PAD layer. A film layer design and a preparation method thereof for a surface acoustic wave device are as follows: Figure 5 As shown, including:

[0047] like Figure 5 (a), a filter pattern is fabricated on the substrate surface according to a microelectronics process to obtain a PAD layer;

[0048] like Figure 5 (b)-(d), making PAD binding blocks on the surface of the PAD layer according to the microelectronics lift-off process (coating, exposure, development, coating, and lift-off);

[0049] like Figure 5 (e) using microelectronics technology to fabricate and pattern a WALL PI layer on the substrate surface and the PAD layer surface;

[0050] like Figure 5(f) Using microelectronic technology to make a ROOF PI layer on the surface of the WALL PI layer and pattern it;

[0051] like Figure 5 (g) using a PVD process to plate a UBM layer on the sidewall of the WALL PI layer, the sidewall of the ROOF PI layer, the exposed surface of the PAD layer, and the exposed surface of the PAD binding block, so as to achieve connection between the UBM layer and the PAD binding block;

[0052] like Figure 5 (h) WLP packaging is completed using electroplating process and printed solder ball process.

[0053] In the present invention, unless otherwise clearly stipulated and limited, the terms such as "installation", "setting", "connection", "fixation" and "rotation" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, ordinary technicians in this field can understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0054] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A membrane layer design of a surface acoustic wave device and a method for preparing the same, characterized in that: The following steps are involved: S1. A filter pattern is formed on the surface of the substrate to obtain a PAD layer according to a microelectronic process; and then a bonding film layer is formed on the surface of the PAD layer; S2. A WALL PI layer is fabricated on the surface of the substrate and the surface of the PAD layer according to the microelectronics process; and a ROOF PI layer is fabricated on the surface of the WALL PI layer; S3. Use PVD process to plate UBM layer on the side wall of WALL PI layer, the side wall of ROOF PI layer, the exposed surface of PAD layer, and the exposed surface of bonding film layer; S4. WLP packaging is completed using electroplating process and solder ball printing process.

2. The membrane layer design and preparation method of a surface acoustic wave device according to claim 1, characterized in that: Step S1 is to make a bonding film layer on the surface of the PAD layer, that is, to make a plurality of raised PAD bonding blocks on the surface of the PAD layer; when making the UBM layer, each PAD block is completely covered by the UBM layer material.

3. The membrane layer design and preparation method of a surface acoustic wave device according to claim 2, characterized in that: All PAD binding blocks are arranged in a matrix form with equal intervals.

4. The membrane design and preparation method of a surface acoustic wave device according to claim 2, characterized in that: The angle between the side surface of the PAD binding block and the surface of the PAD layer is between 0 and 180 degrees.

5. The membrane design and preparation method of a surface acoustic wave device according to claim 1, characterized in that: Step S1 is to make a bonding film layer on the surface of the PAD layer to make a groove in the PAD layer; when making the UBM layer, the groove is completely filled with the UBM layer material.

6. The membrane design and preparation method of a surface acoustic wave device according to claim 4, characterized in that: The angle between the groove side and the groove bottom is between 0 and 180 degrees.

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