A stress buffer packaging structure for MEMS devices

Abstract

The present invention discloses a stress buffer packaging structure for a MEMS device, which relates to the field of chip packaging technology. The key points of its technical solution include a packaging shell and a MEMS chip, wherein a stress buffer pad for carrying the MEMS chip is fixedly arranged in the packaging shell, and an adhesive is arranged between the stress buffer pad and the MEMS chip; the stress buffer pad includes a substrate, and at least two protrusions of different heights are arranged on the end face of the substrate opposite to the MEMS chip. The present invention forms a three-dimensional graphic feature on the front side of the stress buffer pad, which can not only realize the bonding and fixing of the MEMS chip and greatly reduce the stress coupling between the MEMS chip and the packaging shell, but also provide the MEMS chip with sufficient adhesive strength and greatly improve the consistency of the adhesive and the adhesive stress.

Description

Technical Field

[0001] The present invention relates to the technical field of chip packaging, and more specifically, to a stress buffer packaging structure of a MEMS device. Background Art

[0002] MEMS devices such as gyroscopes, accelerometers, and resonators are very sensitive to mechanical stress because stress can change the stiffness and resonant frequency of the MEMS sensitive structure, causing an undesirable coupling effect between the sensitive structure and external stress or thermal stress. Therefore, how to reduce the internal stress of the MEMS device itself and reduce the impact of external stress on the MEMS device is the key to improving the performance of MEMS devices.

[0003] The packaging stress mainly comes from the thermal stress caused by the mismatch of thermal expansion coefficients between the MEMS chip and the packaging material, and the external stress mainly comes from the SMT of the MEMS device and the changes in the stress state of the PCB carrier caused by mechanical vibration and mechanical shock. These stresses will eventually be transmitted to the MEMS chip, causing abnormal deformation of the MEMS chip, which is manifested as the drift of the zero position and scale factor of the MEMS sensor, and more seriously, leading to functional failure of the MEMS device.

[0004] Most of the existing methods for reducing or isolating stress are to increase the local flexibility of the packaging structure to release the stress that should be transmitted to the MEMS chip on the stress transfer path. Generally, there are the following methods: 1) Use soft glue with low Young's modulus to bond the MEMS chip to basically release the stress in the soft glue layer. The smaller the Young's modulus, the better the stress release effect; 2) Use a single-point or single-sided supported cantilever beam structure to bond or fix the MEMS chip on the underlying structure, which can release most of the stress uploaded from the underlying structure, such as shown in patents such as CN201410306360, CN112225168A, and CN110546516A; 3) Add a flexible platform between the MEMS chip and the underlying structure. The flexible platform is generally suspended and supported on the underlying structure by multiple support beams to play a stress isolation role, such as shown in patents such as CN201911000389.9 and EP1571454B1.

[0005] Although the above method can isolate stress well, it also has the disadvantages of low structural strength or low rigidity and is not suitable for high overload resistance applications. Summary of the invention

[0006] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a stress buffering packaging structure for a MEMS device, which can form a three-dimensional graphic feature on the front side of the stress buffer pad, thereby not only realizing the bonding and fixation of the MEMS chip and greatly reducing the stress coupling between the MEMS chip and the packaging tube shell, but also providing the MEMS chip with sufficient bonding strength, thereby greatly improving the consistency of the bonding glue and the bonding glue stress.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A stress buffering packaging structure of a MEMS device comprises a packaging tube shell and a MEMS chip, wherein a stress buffering pad for carrying the MEMS chip is fixedly arranged in the packaging tube shell, and an adhesive is arranged between the stress buffering pad and the MEMS chip; the stress buffering pad comprises a substrate, and at least two protrusions of different heights are arranged on the end face of the substrate opposite to the MEMS chip.

[0009] Furthermore, the protrusion includes a boss and a convex point, and the height of the convex point is greater than the height of the boss.

[0010] Furthermore, a plurality of convex dot circles are arranged on the substrate, and the convex dot circles are composed of one or more convex dots distributed in a circular area.

[0011] Furthermore, four convex dot circles are arranged on the substrate, and the four convex dot circles are respectively arranged at four vertex corners of the substrate; and the boss is arranged at the center of the substrate.

[0012] Furthermore, three convex dot circles are arranged on the substrate, and the boss and the three convex dot circles are respectively arranged at four vertex corners of the substrate.

[0013] Furthermore, the adhesive simultaneously covers the substrate, the boss and the bump ring to form a full-surface bonding, or the adhesive covers a plurality of the bump rings to form a multi-point bonding, or the adhesive covers the boss and a plurality of the bump rings to form a multi-point bonding, or the adhesive covers the boss to form a single-point bonding.

[0014] Furthermore, the MEMS chip abuts against the bumps.

[0015] Furthermore, the thickness of the substrate is 100 μm to 1000 μm, the height difference between the boss and the substrate is 30 μm to 200 μm, and the height difference between the convex point and the boss is 5 μm to 30 μm.

[0016] Furthermore, the diameter of the convex point is 10 μm to 50 μm, and the diameter of the circular area forming the convex point circle is 300 μm to 900 μm.

[0017] Furthermore, the material of the stress buffer pad is silicon, which is integrally formed after multiple etchings using a deep reactive ion etching process.

[0018] In summary, the present invention has the following beneficial effects:

[0019] 1. Forming three-dimensional graphic features on the front of the stress buffer pad can not only achieve the bonding and fixation of the MEMS chip, greatly reduce the stress coupling between the MEMS chip and the package shell, but also provide sufficient bonding strength for the MEMS chip, greatly improving the consistency of the bonding glue and the bonding glue stress;

[0020] 2. The stress buffer pad with three-dimensional graphic features can fix the adhesive to a specific shape, which can enable the packaging structure to better release the packaging stress while having a higher adhesive strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic structural diagram of a stress buffer packaging structure of a MEMS device in Example 1;

[0022] Figure 2 It is a schematic diagram of the structure of the package tube shell in Example 1;

[0023] Figure 3 The structure of the stress buffer pad in Example 1 is shown in FIG. Figure 1 ;

[0024] Figure 4 The structure of the stress buffer pad in Example 1 is shown in FIG. Figure 2 ;

[0025] Figure 5 is a schematic structural diagram of the stress buffer pad in Example 2;

[0026] Figure 6 This is a structural schematic diagram of a stress buffer packaging structure of a MEMS device in Example 3;

[0027] Figure 7 It is a structural schematic diagram of a stress buffer packaging structure of a MEMS device in Example 4;

[0028] Figure 8 This is a structural schematic diagram of a stress buffer packaging structure of a MEMS device in Example 5.

[0029] In the figure: 1. packaging tube shell; 11. packaging bottom plate; 12. first step layer; 13. second step layer; 14. inner pad; 15. sealing cavity; 2. packaging cover plate; 3. first adhesive; 4. stress buffer pad; 41. substrate; 42. boss; 43. bump circle; 431. bump; 5. second adhesive; 51. boss adhesive point; 52. bump circle adhesive point; 6. MEMS chip; 7. metal wire; 8. third adhesive; 9. ASIC chip. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0031] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

[0032] Embodiment 1:

[0033] A stress buffer packaging structure for a MEMS device, referring to Figures 1 to 4 , which includes a packaging tube shell 1 and a MEMS chip 6, wherein a stress buffer pad 4 for carrying the MEMS chip 6 is fixedly arranged in the packaging tube shell 1, and an adhesive is arranged between the stress buffer pad 4 and the MEMS chip 6; the stress buffer pad 4 includes a substrate 41, and the end surface of the substrate 41 opposite to the MEMS chip 6 is provided with at least two protrusions of different heights; the substrate 41 cooperates with the at least two protrusions of different heights so that a three-dimensional graphic feature is formed on the front side of the stress buffer pad 4, and the feature is used to fix the adhesive to a specific morphology, which can not only realize the bonding and fixing of the MEMS chip and greatly reduce the stress coupling between the MEMS chip and the packaging tube shell, but also provide the MEMS chip with sufficient adhesive strength, greatly improving the consistency of the adhesive and the adhesive stress.

[0034] Reference Figure 1 and Figure 2In this embodiment, the function of the package tube shell 1 is to provide a sealed cavity and lead out electrical signals. The package tube shell 1 can be a ceramic tube shell, a metal tube shell or a plastic tube shell, which is not limited here; specifically, in this embodiment, the package tube shell 1 is a ceramic tube shell, which includes a package base plate 11, a first step layer 12 and a second step layer 13, and an inner pad 14 is arranged on the first step layer 12; the MEMS chip 6 is connected to the inner pad 14 through a metal wire 7 to lead out electrical signals, and a package cover plate 2 is welded on the second step layer 13, so that a sealed cavity 15 is formed in the package tube shell 1; the MEMS chip 6 is placed in the sealed cavity 15, which can protect the MEMS chip; specifically, in this embodiment, the thickness of the first step layer 12 is 0.3mm~2mm, and the thickness of the second step layer 13 is 0.2mm~1mm; for the second step layer 13, a metallized pattern can be made on its surface for metal melting sealing with the alloy solder of the package cover plate 2, and a Kovar alloy ring can also be made for parallel seam welding with the package cover plate 2, which is not limited here.

[0035] Reference Figures 1 to 4 In this embodiment, the protrusions include a boss 42 and a bump 431, and the height of the bump 431 is greater than the height of the boss 42; specifically, in this embodiment, the MEMS chip 6 is in contact with the bump 431 after being installed in place, that is, the higher bump 431 supports and positions the MEMS chip 6, and there is a gap between the boss 42 and the MEMS chip 6; in other optional embodiments, three or more protrusions of different heights can also be set on the substrate 41, which is not limited here.

[0036] Reference Figures 1 to 4 Preferably, in this embodiment, a plurality of bump circles 43 are provided on the substrate 41, and the bump circle 43 is composed of one or more bumps 431 distributed in a circular area; specifically, in this embodiment, three bumps 431 are provided in the bump circle 43, and the three bumps 431 are evenly distributed along the circumferential direction around the center of the circle; the use of the bump circle 43, on the one hand, can improve the support strength of the MEMS chip 6 and greatly improve the consistency of the adhesive and the stress of the adhesive, and on the other hand, can improve the bonding stability of the MEMS chip and greatly reduce the stress coupling between the MEMS chip and the packaging tube shell; of course, in other optional embodiments, the distribution area of ​​the plurality of bumps 431 of the bump circle 43 can also be a triangle, a square or other shapes, which is not limited here.

[0037] Reference Figures 1 to 4Preferably, in this embodiment, four bump circles 43 are provided on the substrate 41, and the four bump circles 43 are respectively provided at the four vertex corners of the substrate 41, and the boss 42 is provided at the center of the substrate 41; adopting the above-mentioned layout method is beneficial to improving the support strength and the uniformity of stress release; of course, the layout method of the boss 42 and multiple bump circles 43 can be adjusted as needed, and there is no restriction here; the cross-sectional shape of the boss 42 can be circular, rectangular or regular polygonal, etc., specifically, in this embodiment, the cross-sectional shape of the boss 42 is rectangular; in this embodiment, the cross-sectional shape of the substrate 41 is also rectangular, and the area of ​​the boss 42 is 1 / 50 to 1 / 10 of the area of ​​the substrate 41, and the area of ​​the substrate 41 is equal to the area of ​​the MEMS chip 6, which is beneficial to taking into account both the stress buffering / release effect and the bonding strength.

[0038] Reference Figures 1 to 4 Preferably, in the present embodiment, the thickness of the substrate 41 is 100μm to 1000μm, the height difference between the boss 42 and the substrate 41 is 30μm to 200μm, and the height difference between the bump 431 and the boss 42 is 5μm to 30μm; that is, a first height difference is formed between the bump 431 and the boss 42, and a second height difference is formed between the boss 42 and the substrate 41. The above two height differences form a three-dimensional graphic feature on the front side of the stress buffer pad 4; preferably, in the present embodiment, the diameter of the bump 431 is 10μm to 50μm, and the diameter of the circular area forming the bump circle 43 is 300μm to 900μm.

[0039] Reference Figures 1 to 4 In this embodiment, the material of the stress buffer pad 4 is silicon, which is etched multiple times using a deep reactive ion etching process, so that the stress buffer pad 4 is formed in one piece; specifically, a double-polished silicon wafer can be taken, and the designed convex dot pattern is transferred to the photoresist on the front side of the silicon wafer through the first steps of coating, exposure, and development. The area outside the convex dot pattern is engraved 5μm to 30μm through the first deep reactive ion etching (DRIE) to form a first height difference. After degumming, the second spraying, exposure, and development are performed to transfer the convex dot pattern and the boss pattern to the photoresist, and then the second DRIE is performed to engrave the area outside the convex dot and boss pattern by 30μm to 200μm to form a second height difference. At this point, the processing of the three-dimensional pattern on the front side of the silicon wafer is completed, and the stress buffer pad 4 can be obtained by finally cutting the wafer.

[0040] Reference Figures 1 to 4In this embodiment, the stress buffer pad 4 and the packaging tube shell 1 are fixed by the first adhesive 3, and the MEMS chip 6 and the stress buffer pad 4 are fixed by the second adhesive 5; preferably, the first adhesive 3 adopts an adhesive with high Young's modulus and good thermal conductor, such as epoxy conductive silver paste, to bond the entire surface of the stress buffer pad 4 to the packaging base plate 11, so that the packaging structure has sufficient basic adhesive strength and low thermal resistance; in this embodiment, the second adhesive 5 adopts a low Young's modulus adhesive, such as silicone, and a plurality of dot adhesives are coated on the bonded stress buffer pad 4, and the height of the dot adhesive should be higher than the bump 431, and the MEMS chip 6 is placed on the stress buffer pad 4 and a certain pressure is applied to make The back side of the MEMS chip 6 contacts the bump 431 on the stress buffer pad 4, thereby fixing the position of the MEMS chip 6, and the bump 431 also plays a supporting role for the MEMS chip 6 in subsequent processes such as wire bonding; after the second adhesive 5 is cured, the back side of the MEMS chip 6 and the front side of the stress buffer pad 4 are fully bonded, and the morphology of the second adhesive 5 is determined by the three-dimensional graphic characteristics of the stress buffer pad 4, that is, the adhesive thickness at the boss 42 is equal to the first height difference of the stress buffer pad 4, and the adhesive thickness in the area outside the boss 42 is equal to the height of the bump 431 (the sum of the first height difference and the second height difference), that is, the adhesive thickness of the second adhesive 5 at the boss 42 is much smaller than the adhesive thickness in the area outside the boss 42.

[0041] Reference Figures 1 to 4 According to the principle of mechanics, for the multilayer structure composed of the MEMS chip 6, the second adhesive 5 and the stress buffer pad 4, the stress transferred from the stress buffer pad 4 to the MEMS chip 6 depends on the morphology of the middle layer (i.e., the second adhesive 5). The smaller the area and the thicker the thickness of the second adhesive 5, the better the stress isolation effect. Therefore, the ideal stress isolation structure is a central single-point support structure or a maximum thickening of the adhesive layer, but there is also a disadvantage of insufficient bonding strength, which will cause the packaging structure to shake too much when subjected to impact, or even fail. In this embodiment, the adhesive area at the central boss 42 is much smaller than the area of ​​the substrate 41, and the thickness is thin, which has the characteristics of a central single-point support structure, that is, the bending moment acting on the MEMS chip is reduced by a small area, and the tangential stiffness is enhanced by a thin thickness. The adhesive in the area outside the boss 42 reduces the bending moment acting on the MEMS chip by a large thickness, thereby reducing the stress coupling between the MEMS chip 6 and the packaging tube shell 1, and finally makes the packaging structure have both good stress buffering or release effect and high bonding strength.

[0042] Embodiment 2:

[0043] A stress buffer packaging structure for a MEMS device, referring to Figure 5Based on Example 1, the difference between this embodiment and Example 1 is that: in this embodiment, a boss 42 and three bump circles 43 are provided on the substrate 41, and the boss 42 and the three bump circles 43 are respectively provided at the four vertex corners of the substrate 41, and the heights of the substrate 41, the boss 42 and the bump 431 are increased gradually, forming another three-dimensional graphic feature on the front side of the stress buffer pad 4.

[0044] Embodiment 3:

[0045] A stress buffer packaging structure for a MEMS device, referring to Figures 1 to 4 as well as Figure 6 , based on Example 1, the difference between this embodiment and Example 1 is that: in this embodiment, the second adhesive for bonding the MEMS chip 6 does not adopt full-surface bonding, but multi-point bonding, specifically five adhesive points, including the boss adhesive point 51 and the bump circle adhesive point 52; the position and morphology of the five adhesive points are determined by the position and morphology of the boss 42 and the bump circle 43, that is, the area of ​​the boss adhesive point 51 is approximately the area of ​​the boss 42, the adhesive thickness is equal to the first height difference, the diameter of the bump circle adhesive point 52 is approximately the diameter of the bump circle 43, and the adhesive thickness is the sum of the first height difference and the second height difference; compared with Example 1, the stress buffering or releasing effect can be improved.

[0046] Reference Figure 6 In this embodiment, the ASIC chip 9 is fixed on the MEMS chip 6 by the third adhesive 8 to form a stacked integrated package of the mechanical electronic system.

[0047] Embodiment 4:

[0048] A stress buffer packaging structure for a MEMS device, referring to Figures 1 to 4 as well as Figure 7 , based on Example 1, the difference between this embodiment and Example 1 is that: the second adhesive for bonding the MEMS chip 6 in this embodiment does not adopt full-surface bonding, but multi-point bonding, specifically four bump circle adhesive points 52; the position and morphology of the four bump circle adhesive points 52 are determined by the position and morphology of the bump circle 43, that is, the diameter of the four bump circle adhesive points 52 is approximately the bump circle diameter, and the adhesive thickness is the sum of the first height difference and the second height difference. The larger the sum value and the smaller the bump circle diameter, the better the stress release of the four adhesive points; at the same time, in this embodiment, the second adhesive is changed from a soft adhesive with a low Young's modulus to a hard adhesive with a higher Young's modulus (such as epoxy adhesive, etc.), and the Young's modulus of the hard adhesive is generally 1 to 5GPa, which can enhance the rigidity of the bonding structure; the packaging structure in this embodiment has the advantages of high adhesive strength, good stress release effect, sufficient resonance reaction force support, etc., and is suitable for the packaging of high-quality factor resonant devices such as MEMS oscillators and MEMS gyroscopes.

[0049] Embodiment 5:

[0050] A stress buffer packaging structure for a MEMS device, referring to Figures 1 to 4 as well as Figure 8 Based on Example 3, the difference between this embodiment and Example 3 is that: in this embodiment, the second adhesive is changed from five-point bonding of soft glue with low Young's modulus to single-point bonding of hard glue with higher Young's modulus (such as epoxy glue, etc.), and the adhesive point is the boss adhesive point 51; the position and morphology of the adhesive are determined by the position and morphology of the boss 42, that is, the area of ​​the boss adhesive point 51 is approximately the boss area, and the adhesive thickness is the first height difference; in this embodiment, the MEMS chip packaging structure is a central single-point support structure, and there is no fixed connection between the bump 431 and the MEMS chip 6, but it can play a certain vertical support role. Reducing the area of ​​the boss 42 can improve the stress isolation effect, and increasing the area of ​​the boss 42 can increase the adhesive strength. Taking a compromise optimization can take into account both stress isolation and adhesive strength.

[0051] Reference Figure 8 At the same time, in this embodiment, the ASIC chip 9 is fixed on the packaging base plate 11 of the packaging tube shell 1 through the third adhesive 8 to form a flat integrated package of the mechanical and electronic system.

Claims

1. A stress buffer packaging structure of a MEMS device, comprising a packaging tube shell and a MEMS chip, characterized in that: A stress buffer pad for carrying the MEMS chip is fixedly arranged in the packaging tube shell, and a bonding adhesive is arranged between the stress buffer pad and the MEMS chip; the stress buffer pad comprises a substrate, and at least two protrusions with different heights are arranged on the end surface of the substrate opposite to the MEMS chip; The protrusion includes a boss and a convex point, and the height of the convex point is greater than the height of the boss; The stress buffer pad is integrally formed, and the material of the stress buffer pad is silicon.

2. The stress buffer packaging structure of a MEMS device according to claim 1, characterized in that: A plurality of convex dot circles are arranged on the substrate, and the convex dot circles are composed of one or more convex dots distributed in a circular area.

3. The stress buffer packaging structure of the MEMS device according to claim 2, characterized in that: Four convex dot circles are arranged on the substrate, and the four convex dot circles are respectively arranged at the four vertex corners of the substrate; the boss is arranged at the center of the substrate.

4. The stress buffer packaging structure of a MEMS device according to claim 2, characterized in that: The substrate is provided with three convex dot circles, and the boss and the three convex dot circles are respectively arranged at the four vertex corners of the substrate.

5. The stress buffer packaging structure of a MEMS device according to claim 2, characterized in that: The adhesive simultaneously covers the substrate, the boss and the bump ring to form full-surface bonding, or the adhesive covers multiple bump rings to form multi-point bonding, or the adhesive covers the boss and multiple bump rings to form multi-point bonding, or the adhesive covers the boss to form single-point bonding.

6. The stress buffer packaging structure of a MEMS device according to claim 2, characterized in that: The MEMS chip is in contact with the bumps.

7. The stress buffer packaging structure of a MEMS device according to claim 1, characterized in that: The thickness of the substrate is 100 μm-1000 μm, the height difference between the boss and the substrate is 30 μm-200 μm, and the height difference between the convex point and the boss is 5 μm-30 μm.

8. The stress buffer packaging structure of a MEMS device according to claim 3, characterized in that: The diameter of the convex point is 10 μm to 50 μm, and the diameter of the circular area forming the convex point circle is 300 μm to 900 μm.

9. The stress buffer packaging structure of a MEMS device according to claim 1, characterized in that: The stress buffer pad is integrally formed after multiple etchings using a deep reactive ion etching 4 process.

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