MEMS Integrated Packaging Structure and Its Preparation Method

Abstract

The present invention discloses a MEMS integrated packaging structure and a preparation method thereof. The MEMS integrated packaging structure includes a resin substrate, on which a MEMS chip is flip-chip mounted. There is a spacing equal to the height of solder balls between the MEMS chip and the resin substrate, and the solder balls are led to the outer surface of the resin substrate through pins. The outside of the MEMS chip is coated with a vacuum cavity forming film layer. The joint between the vacuum cavity forming film layer and the resin substrate is located outside the solder balls, so that a vacuum cavity is formed at the spacing between the MEMS chip and the resin substrate. The outside of the vacuum cavity forming film layer is encapsulated with the resin substrate through epoxy injection molding to form an epoxy resin coating layer. The present invention realizes the first packaging of the MEMS chip and the resin substrate through the vacuum cavity forming film process, and forms a vacuum cavity between the MEMS chip and the resin substrate. Then, the second packaging is carried out through high-pressure injection molding. While achieving the same effect of two-packaging, the packaging waiting time and process flow are saved, and the packaging cost is reduced.

Description

Technical Field

[0001] The present invention relates to the field of chip packaging, and particularly to a MEMS integrated packaging structure and a preparation method thereof. Background Art

[0002] Since the packaging of integrated circuit devices has evolved from the development of single components to the integration of multiple components, driven by the improvement of product performance and the demand for thinness, lightness, and low power consumption, it has entered a new stage of packaging integration. Under the guidance of this development direction, two new mainstream trends in the electronics industry have emerged: System-on-Chip (SoC) and System-in-Package (SIP).

[0003] SoC and SIP are very similar. Both integrate a system containing logic components, memory components, and even passive components into one unit. SoC starts from the design perspective and highly integrates the components required by the system onto a single chip; SIP starts from the packaging perspective and packages different chips side by side or stacked, preferentially assembling multiple active electronic components with different functions, optional passive devices, and other devices such as MEMS or optical devices together to form a single standard package with a certain function.

[0004] The elements constituting the SIP technology are the packaging carrier and the assembly process. The former includes PCB, LTCC, and Silicon Submount, and the latter includes traditional packaging processes (Wire bond and Flip Chip) and SMT equipment. Passive devices are an important part of SIP, such as traditional capacitors, resistors, inductors, etc. Some of them can be integrated with the carrier, and others such as inductors and capacitors with high precision, high Q value, and high numerical value are assembled on the carrier through SMT.

[0005] The SIP packaging technology arranges and assembles multiple bare chips or modules. If classified by the arrangement method, it can be generally divided into planar 2D packaging and 3D packaging structures. Compared with 2D packaging, the stacked 3D packaging technology can increase the number of wafers or modules used, thereby increasing the number of wafer layers that can be placed in the vertical direction and further enhancing the function integration ability of the SIP technology. The internal bonding technology can be simple wire bonding, flip chip bonding, or a combination of both.

[0006] In addition, besides the 2D and 3D packaging structures, a method of integrating components with a multifunctional substrate can also be adopted, that is, different components are embedded in the multifunctional substrate to achieve the purpose of function integration. Different chip arrangement methods, combined with different internal bonding technologies, make the packaging forms of SIP diversified, and can be customized or flexibly produced according to the needs of customers or products.

[0007] Currently, the SiP system integration packaging solutions mainly target and are applied to the packaging of IC integrated circuits. There is no system integration method for MEMS devices with cavity structures using resin substrates as carriers. The conventional method for devices with cavity structures is secondary packaging. First, a primary packaging is performed on the MEMS sensitive device to form a protection structure, such as wafer-level packaging, where a silicon wafer etched on the chip surface is covered as an upper cover, and through the bonding process, the MEMS device and the silicon-level upper cover are bonded together to form a cavity structure. Then, the pins are led out through processes such as TSV to form an independent device with a cavity structure. Then, the MEMS device is mounted on the substrate by flip-chip soldering or SMT, and then secondary hybrid integration packaging is carried out with other ICs and resistors and capacitors. The packaging process is complex, the volume is large, the thickness is difficult to reduce, the cycle is long, the cost is high, and the efficiency is low. Summary of the Invention

[0008] Therefore, to solve the above problems, the present invention provides a MEMS integrated packaging structure and its preparation method.

[0009] The present invention is realized through the following technical solutions:

[0010] The MEMS integrated packaging structure includes a resin substrate. An MEMS chip is flip-mounted on the resin substrate. There is a space with the height of solder balls between the MEMS chip and the resin substrate, and the solder balls are led to the outer surface of the resin substrate through pins. The outside of the MEMS chip is coated with a vacuum cavity forming film layer. The joint of the vacuum cavity forming film layer and the resin substrate is located outside the solder balls, so that a vacuum cavity is formed at the space between the MEMS chip and the resin substrate. The outside of the vacuum cavity forming film layer is encapsulated with the resin substrate through epoxy molding compound to form an epoxy resin coating layer.

[0011] Preferably, the height of the vacuum cavity is 10um - 15um.

[0012] Preferably, stacked chips are selectively arranged on the resin substrate. The stacked chips include a first chip flip-mounted on the resin substrate and a second chip mounted upright on the first chip. The first chip and the resin substrate are interconnected through pins, and the leads of the second chip and the substrate are interconnected through wire bonding.

[0013] Preferably, passive components are selectively disposed on the resin substrate. The passive components include capacitors and resistors, and a solder paste layer is disposed between the passive components and the substrate.

[0014] Preferably, the epoxy resin coating layer coats the outside of the vacuum cavity forming film layer, the first chip, the second chip, and the resistor and capacitor components, encapsulating the MEMS chip, and / or the stacked chip, and / or the passive components together.

[0015] A method for preparing a MEMS integrated packaging structure includes the following steps:

[0016] S1. After printing solder paste on the surface of the resin substrate, flip chips and passive components are mounted on the surface of the resin substrate, and the flip chips and passive components are soldered and fixed on the surface of the resin substrate by means of reflow soldering;

[0017] S2. Bake and cure the resin substrate, and perform plasma cleaning on the cured resin substrate and the flip chips and passive components mounted on the resin substrate together, for later use;

[0018] S3. Electroplate and implant solder balls on the surface of the MEMS chip. The diameter of the flip-chip solder balls of the MEMS chip is 65 + / - 5um, and the height is 45 + / - 5um. Then, the MEMS chip is cut and shaped according to the corresponding assembly position of the MEMS chip on the resin substrate. After cutting, the MEMS chip is flip-mounted on the resin substrate after the step S2 by means of thermocompression ultrasonic soldering;

[0019] S4. Form a layer of vacuum cavity forming film layer outside the MEMS chip through a vacuum film forming and cavity forming step;

[0020] S5. Perform high-pressure injection molding to form an epoxy resin coating layer, and further bake and cure the injection-molded product to form a MEMS integrated packaging structure.

[0021] Preferably, the "vacuum film forming and cavity forming step" in the step S4 is specifically:

[0022] S41. Stick a semi-cured epoxy film outside the MEMS chip. The semi-cured epoxy film is of the brand NAGASE A2034 or an alternative material with similar performance. The thickness of the semi-cured epoxy film is 4 - 20um; the specific gravity is 1.61; the Tg temperature value is 90°C; the flexural modulus is 8GPa; the gel time under the condition of 150°C is 90s;

[0023] S42. Place and fix the resin substrate in the vacuum chamber of the film laminator;

[0024] S43. The first process change: The vacuum chamber is evacuated. During this evacuation process, the inside of the vacuum chamber is rapidly heated with a temperature rise of 5 °C / s and maintained at a constant temperature of 60 ± 2 °C for a total time of 20 ± 5 s. During this process, the semi-cured epoxy film liquefies from a solid state into a sol state.

[0025] S44. The second process change: The vacuum chamber maintains a constant temperature of 60 ± 2 °C, and the inside of the vacuum chamber is pressurized. The pressurization time is 10 + 2 s and the pressure is 0.1 + 0.02 Mpa. During this process, the semi-cured epoxy film undergoes flow filling and preliminary curing in a sol state. The height of the formed vacuum cavity is between 10 μm and 15 μm.

[0026] S45. Baking and curing of the semi-cured epoxy film to achieve complete curing. The baking temperature is 150 ± 3 °C and the baking time is 180 ± 20 minutes.

[0027] Preferably, the step S1 further includes steps of performing plasma cleaning and filling the bottom of the flip chip with epoxy resin.

[0028] Preferably, the MEMS integrated packaging structure can be packaged in a single group structure, or can be packaged together with a group of chips and / or passive components, and cut into single particles after packaging.

[0029] The beneficial effects of the technical solution of the present invention are mainly reflected in:

[0030] 1. This solution realizes the first packaging of the MEMS chip and the resin substrate through the vacuum cavity forming and film covering process, and forms a vacuum cavity between the MEMS chip and the resin substrate. Then, the second packaging is carried out through high-pressure injection molding. While achieving the same two-packaging effects, it saves the packaging waiting time and process flow, and reduces the packaging cost.

[0031] 2. In this solution, the vacuum cavity between the MEMS chip and the resin substrate is arranged at the interval of pin interconnection between the MEMS chip and the resin substrate. Compared with the existing packaging structure, it reduces the thickness of a layer of vacuum structure and realizes the thinning of the MEMS integrated packaging structure.

[0032] 3. In this solution, other chips are stacked in a way that combines face-up assembly and flip-chip assembly, reducing the mounting area of the packaging structure and making reasonable use of the longitudinal space of the packaging structure. Description of the Drawings

[0033] Figure 1 : It is a cross-sectional view of the MEMS integrated packaging structure in the present invention. Detailed Embodiments

[0034] To clearly and detailedly illustrate the objectives, advantages and features of the present invention, the following non-limiting description of the preferred embodiments will be used for illustration and explanation. This embodiment is only a typical example of applying the technical solution of the present invention. Any technical solution formed by equivalent replacement or equivalent transformation falls within the scope of protection required by the present invention.

[0035] At the same time, it is stated that in the description of the solution, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "front", "rear", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of description and simplification of the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0036] In addition, the terms "first" and "second" in this solution are only used for descriptive purposes and cannot be understood as indicating or implying the ranking of importance or implicitly indicating the quantity of the technical features shown. Therefore, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the present invention, the meaning of "a plurality" is two or more, unless otherwise specifically defined.

[0037] The present invention discloses a MEMS integrated packaging structure and a preparation method thereof, as Figure 1 shown. The MEMS integrated packaging structure includes a resin substrate 1, on which a MEMS chip 2 is flip-chip mounted. There is a space with the height of solder balls 3 between the MEMS chip 2 and the resin substrate 1, and the solder balls 3 are led to the outer surface of the resin substrate 1 through pins 7. The solder balls 3 are welded to the surface of the MEMS chip 2 and fixed between the MEMS chip 2 and the resin substrate 1 by thermocompression ultrasonic welding. The initial diameter of the flip-chip solder balls 3 of the MEMS chip 2 is 65+ / -5um, and the initial height is 45+ / -5um. After being fixed on the resin substrate 1 by thermocompression ultrasonic welding, the height of the solder balls 3 is 10um-15um. At this time, the spacing distance between the MEMS chip 2 and the resin substrate 1 is 10um-15um.

[0038] Specifically, the MEMS chip 2 is externally coated with a vacuum cavity forming film layer 4, the vacuum cavity forming film layer 4 is closely attached to the outer surface of the MEMS chip 2, and the joint of the vacuum cavity forming film layer 4 and the resin substrate 1 is located outside the solder ball 3, so that a sealed vacuum cavity 6 is formed at the interval between the MEMS chip 2 and the resin substrate 1. Since the solder ball 3 is fixed on the resin substrate 1 by thermocompression ultrasonic welding, the interval distance between the MEMS chip 2 and the resin substrate 1 is 10um - 15um, and the height of the vacuum cavity 6 is also between 10um - 15um.

[0039] Specifically, stacked chips are selectively arranged on the resin substrate 1. The stacked chips include a first chip 8 flip-chip mounted on the resin substrate 1 and a second chip 9 mounted on the first chip 8 in a face-up manner. The first chip 8 and the resin substrate 1 are interconnected through pins 7, and the leads of the second chip 9 and the substrate are interconnected through wire bonding. The types of the first chip 8 and the second chip 9 can be selected according to the different functional requirements of the MEMS integrated packaging structure, and one or more groups of stacked chips can also be provided.

[0040] Specifically, passive components 10 are selectively arranged on the resin substrate 1. The passive components 10 include capacitors and resistors. A solder paste layer is arranged between the passive components 10 and the substrate to facilitate soldering the passive components 10 on the resin substrate 1. Specifically, a solder paste layer can also be arranged between the resin substrate 1 and the stacked chips to facilitate soldering the stacked chips.

[0041] Specifically, the outside of the vacuum cavity forming film layer 4 is encapsulated with the resin substrate 1 through epoxy molding compound to form an epoxy resin coating layer 5. The epoxy resin coating layer 5 covers the outside of the vacuum cavity forming film layer 4, the first chip 8, the second chip 9, and resistors and capacitor components, encapsulating the MEMS chip 2, and / or the stacked chips, and / or the passive components 10 together. Specifically, the height after the stacked chips and the passive components 10 are assembled on the resin substrate 1 is less than or equal to the height after the MEMS chip 2 is assembled on the resin substrate 1 to control the overall thickness of the MEMS integrated packaging structure and achieve thinning.

[0042] A method for preparing a MEMS integrated packaging structure includes the following steps:

[0043] S1. After printing solder paste on the surface of the resin substrate 1, flip chips and passive components 10 are mounted on the surface of the resin substrate 1, and the flip chips and the passive components 10 are soldered and fixed on the surface of the resin substrate 1 by means of reflow soldering;

[0044] Specifically, the step S1 further includes the steps of performing plasma cleaning and filling the bottom of the flip chip with epoxy resin. Specifically, after the flip chip and the passive component 10 are soldered on the surface of the resin substrate 1, the resin substrate 1 with the flip chip and the passive component 10 mounted thereon is first washed and dried and / or subjected to plasma cleaning, and then epoxy resin is filled in the gap between the bottom of the flip chip and the passive component 10 and the resin substrate 1. After filling the epoxy resin, the epoxy resin is cured by baking and the resin substrate 1, the flip chip and the passive component 10 are subjected to plasma cleaning again.

[0045] Specifically, a front-mounted chip may be optionally mounted on the flip chip. The flip chip and the front-mounted chip form a set of stacked chips, or through SMT (Surface Mount Technology / Surface Mounting Technology), the chip assembly is completed by means of reflow soldering. The stacked chips can complete the traction of the pins 7 through wire bonding or through the TSV process.

[0046] S2. Bake and cure the resin substrate 1, and perform plasma cleaning on the cured resin substrate 1, the flip chip and the passive component 10 mounted on the resin substrate 1 together for standby;

[0047] S3. After electroplating and implanting solder balls 3 on the surface of the MEMS chip 2, the MEMS chip 2 is cut and shaped according to the corresponding assembly position of the MEMS chip 2 on the resin substrate 1. After cutting is completed, the MEMS chip 2 is flip-mounted on the resin substrate 1 after the step S2 by means of thermocompression ultrasonic welding;

[0048] Specifically, the thermocompression ultrasonic welding method means that the solder ball 3 is first welded to the surface of the MEMS chip 2, and then the MEMS chip 2 and the solder ball 3 are press-connected to the surface of the resin substrate 1 through thermocompression ultrasonic welding. The solder ball 3 is a gold ball with a diameter of 65 + / - 5 um and a height of 45 + / - 5 um. After the thermocompression ultrasonic welding is completed, the height of the solder ball 3 is compressed to 10 um - 15 um after being extruded, so that the spacing distance between the MEMS chip 2 and the resin substrate 1 is controlled within 10 um - 15 um. After the solder ball 3 is welded to the surface of the resin substrate 1, the solder ball 3 is connected to the lead 7 led to the outer surface of the resin substrate 1. Specifically, a plurality of through holes for guiding the lead 7 are provided on the resin substrate 1 at the assembly position corresponding to the MEMS chip 2 and penetrate through the resin substrate 1. The lead 7 passes through the through hole from the outside of the resin substrate 1 to the encapsulation surface of the resin substrate 1 and is drawn to the position of the solder ball 3 to be connected to the solder ball 3. Further, the through hole can be provided at the welding point of the solder ball 3. After the lead 7 passes through the through hole, it is directly connected to the bottom of the solder ball 3. This lead 7 drawing method is prior art and will not be elaborated here.

[0049] S4. A vacuum cavity coating layer 4 is formed outside the MEMS chip 2 through a vacuum film coating and cavity forming step;

[0050] Specifically, the "vacuum film coating and cavity forming step" in step S4 is specifically as follows:

[0051] S41. A semi-cured epoxy film is pasted outside the MEMS chip 2. The semi-cured epoxy film is of the NAGASE A2034 brand or an alternative material with similar performance. The thickness of the semi-cured epoxy film is 4 - 20 um; the specific gravity is 1.61; the Tg temperature value is 90 °C; the flexural modulus is 8 GPa; the gel time at 150 °C is 90 s;

[0052] S42. The resin substrate 1 is placed and fixed in the vacuum chamber of the film laminator;

[0053] S43. In the first process change process, the vacuum chamber is evacuated. During this evacuation process, the vacuum chamber is rapidly heated with a temperature rise of 5 °C / s and maintained at a constant temperature of 60 ± 2 °C for a total time of 20 ± 5 s; during this process, the semi-cured epoxy film changes from a solid state to a liquefied sol state;

[0054] S44. In the second process change process, the vacuum chamber is maintained at a constant temperature of 60 ± 2 °C, and the vacuum chamber is pressurized. The pressurization time is 10 + 2 s and the pressure is 0.1 + 0.02 Mpa; during this process, the semi-cured epoxy film undergoes flow filling and preliminary curing in a sol state; the height of the formed vacuum cavity 6 is between 10 um - 15 um;

[0055] S45. Bake and cure the semi-cured epoxy film to achieve complete curing. The baking temperature is 150 ± 3°C, and the baking time is 180 ± 20 minutes.

[0056] S5. High-pressure injection molding to form an epoxy resin coating layer 5, and further bake and cure the molded product to form a MEMS integrated packaging structure.

[0057] Specifically, the MEMS integrated packaging structure can be packaged as a single structure, or can be packaged together with one or more groups of chips and / or passive components 10. It can also package multiple groups of MEMS integrated packaging structures simultaneously and cut them into single particles after packaging.

[0058] There are still various implementation manners of the present invention. All technical solutions formed by equivalent transformation or equivalent substitution fall within the protection scope of the present invention.

Claims

1. A method for preparing a MEMS integrated packaging structure, characterized in that: For preparing a MEMS integrated packaging structure, the MEMS integrated packaging structure includes a resin substrate (1), on which a MEMS chip (2) is flip-chip mounted. There is a space with the height of solder balls (3) between the MEMS chip (2) and the resin substrate (1), and the solder balls (3) are led to the outer surface of the resin substrate (1) through pins (7). The outside of the MEMS chip (2) is coated with a vacuum cavity forming film layer (4). The joint between the vacuum cavity forming film layer (4) and the resin substrate (1) is located outside the solder balls (3), so that a vacuum cavity (6) is formed at the space between the MEMS chip (2) and the resin substrate (1). The outside of the vacuum cavity forming film layer (4) is encapsulated with the resin substrate (1) through epoxy injection molding to form an epoxy resin coating layer (5); the height of the vacuum cavity (6) is 10um - 15um; on the resin substrate (1), stacked chips are selectively arranged. The stacked chips include a first chip (8) flip-chip mounted on the resin substrate (1) and a second chip (9) mounted above the first chip (8) in a face-up manner. The first chip (8) is interconnected with the resin substrate (1) through pins (7), and the leads of the second chip (9) are interconnected with the substrate through wire bonding; on the resin substrate (1), passive components (10) are selectively arranged. The passive components (10) include capacitors and resistors, and a solder paste layer is arranged between the passive components (10) and the substrate; the epoxy resin coating layer (5) covers the outside of the vacuum cavity forming film layer (4), above the first chip (8), above the second chip (9), and the resistor and capacitor components, encapsulating the MEMS chip (2), and / or the stacked chips, and / or the passive components (10) together; Including the following steps: S1. After printing solder paste on the surface of the resin substrate (1), the flip-chip and the passive components (10) are mounted on the surface of the resin substrate (1), and the flip-chip and the passive components (10) are welded and fixed on the surface of the resin substrate (1) by means of reflow soldering; S2. Bake and cure the resin substrate (1), and perform plasma cleaning on the cured resin substrate (1) and the flip-chip and the passive components (10) mounted on the resin substrate (1) together, and set aside; S3. Electroplate and implant solder balls (3) on the surface of the MEMS chip (2). The diameter of the flip-chip solder balls (3) of the MEMS chip (2) is 65 ± 5um, and the height is 45 ± 5um. Then, according to the corresponding assembly position of the MEMS chip (2) on the resin substrate (1), the MEMS chip (2) is cut and shaped. After cutting, the MEMS chip (2) is flip-chip mounted on the resin substrate (1) after the step S2 by means of thermocompression ultrasonic welding; S4. Form a vacuum cavity forming film layer (4) outside the MEMS chip (2) through a vacuum film forming and cavity forming step; S5. High-pressure injection molding to form an epoxy resin coating layer (5), and further baking and curing the injection-molded product to form a MEMS integrated packaging structure; In the step S4, the "vacuum film lamination to form a cavity step" is specifically as follows: S41. Stick a semi-cured epoxy film outside the MEMS chip (2). The grade of the semi-cured epoxy film is NAGASE A2034 or an alternative material with similar performance. The thickness of the semi-cured epoxy film is 4 - 20 um; specific gravity is 1.61; Tg temperature value is 90 °C; flexural modulus is 8 GPa; gel time at 150 °C is 90 s; S42. Place and fix the resin substrate (1) in the vacuum chamber of the film laminator; S43. In the first process change process, the vacuum chamber is evacuated. During this evacuation process, the inside of the vacuum chamber is rapidly heated with a temperature rise of 5 °C / s, and kept at a constant temperature of 60 ± 2 °C for a total time of 20 ± 5 s; during this process, the semi-cured epoxy film changes from a solid state to a sol state; S44. In the second process change process, the vacuum chamber is kept at a constant temperature of 60 ± 2 °C, and pressure is applied to the inside of the vacuum chamber. The pressure application time is 10 + 2 s and the pressure is 0.1 + 0.02 Mpa; during this process, the semi-cured epoxy film undergoes flow filling and preliminary curing in a sol state; the height of the formed vacuum cavity (6) is 10 um - 15 um; S45. Baking and curing of the semi-cured epoxy film to achieve complete curing. The baking temperature is 150 ± 3 °C and the baking time is 180 ± 20 minutes.

2. The preparation method of the MEMS integrated packaging structure according to claim 1, wherein: The step S1 further includes performing plasma cleaning and filling the bottom of the flip chip with epoxy resin.

3. The preparation method of the MEMS integrated packaging structure according to claim 1, characterized in that: The single-group structure of the MEMS integrated packaging structure is packaged alone, or packaged together with a group of chips and / or passive components (10), and cut into single particles after packaging is completed.

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