CN114195091A - MEMS packaging method - Google Patents

Abstract

The invention relates to a MEMS packaging method, which comprises the following steps: the chip set is attached to the substrate, and the gold wire is connected between the chip set and the substrate in a bonding mode after baking; the method comprises the following steps of spot-coating solder paste on copper foil on the periphery of a substrate, covering a packaging shell on the solder paste of the substrate, and melting the solder paste through reflow soldering to weld the packaging shell and the substrate; the upper surface of the top surface of the packaging shell is attached to an inverted mold containing epoxy resin, and after heating, the epoxy resin is extruded into the cavity of the packaging shell through the small holes and blocks the small holes; curing the product to cure the epoxy resin in the cavity and the small hole of the packaging shell; carrying out laser printing on the product according to the requirement; the product is cut into individual finished products by a cutting machine. The method achieves the purpose of plugging the small holes, does not increase the size of the product, does not improve the production cost of the product, and has strong practicability.

Description

MEMS packaging method

Technical Field

The invention relates to a packaging method, in particular to a low-cost MEMS packaging method.

Background

With the deep development of MEMS, the application of MEMS is more and more extensive, and the requirements for MEMS, such as noise requirements, drift and the like, for MEMS are higher, and with the development of electronic products, higher requirements for detection accuracy and the like by using MEMS devices are provided.

The MEMS detection is realized through micromechanical motion, mechanical stress influencing a micromachine is one of main factors which are troubling the performance improvement of the MEMS, the stress source is mainly caused by different materials which are mutually contacted after the MEMS is packaged, such as plastic packaging resin for packaging an MEMS chip, welding reflow after a cover is attached, and the like, particularly after the currently developed multi-chip is assembled with a SiP, the multi-chip is applied to thin and small electronic products, the requirement on the appearance volume of the MEMS products is smaller and smaller, meanwhile, a plurality of materials are placed together through packaging to generate stress influence, and the stress influence is particularly obvious when the temperature changes, so that the characteristics of the products such as sensitivity, zero drift and the like are deteriorated.

After that, companies try to adopt the metal cap packaging structure with the opening, and the metal cap after the sealing needs to be opened on the upper part due to the high temperature of the backflow of the subsequent electronic assembly, but the product after the sealing is in a small hole communicated with the outside in the using process, and external dust, moisture and the like can enter the sensor body to influence the product characteristics, so that the gradual deterioration of the signal of the MEMS sensor after long-term use cannot be avoided.

Therefore, the process of opening the holes at the edge is realized, and the mode of coating resin vacuum pumping is adopted, so that the problems that the small holes are closed, and the inner cavity is vacuum, so that the small holes which are subjected to high-temperature backflow are expanded are solved. Although the vacuum film covering technology is mature, the products have the defects that the film covering resin has a certain thickness, usually the thickness reaches 0.15mm, so that the thickness of the products is increased by 0.15 mm; moreover, the price of the film-coated resin is expensive, the film-coated resin is an imported material at present, and the price of one piece of resin with the thickness of 90 x 90mm exceeds 100 yuan, so that the cost of each piece of product rises by nearly 0.1 yuan; in addition, the film covering process also needs to add expensive film covering equipment, the single machine reaches 20 ten thousand dollars, and the cost of the finished product which is a depreciated product is not small

Due to the increase of the product thickness, the ultrathin application of the product required by the client is limited, and the market popularization is influenced; the rising cost of the product affects the competitiveness of the product.

Disclosure of Invention

In order to overcome the defects, the invention provides an MEMS packaging method, which adopts the traditional plastic packaging resin material, utilizes a vacuum oven and combines a reverse packaging mould, squeezes molten plastic packaging resin into a packaging shell through small holes under the condition of vacuumizing, flows a resin layer with the thickness of about 0.1mm into the packaging shell through high-temperature heat preservation at 170 ℃, and achieves the purpose of plugging the small holes through post-curing.

The technical scheme adopted by the invention for solving the technical problem is as follows:

a MEMS packaging method comprising the steps of:

step 1: assembling: the chip set is attached to the substrate, and the gold wire is connected between the chip set and the substrate in a bonding mode after baking;

step 2: drawing solder paste and a cover cap: the method comprises the following steps of spot-coating solder paste on copper foil on the periphery of a substrate, covering a packaging shell on the solder paste of the substrate, melting the solder paste through reflow soldering, and welding the packaging shell and the substrate to obtain a semi-finished product, wherein the top surface of the packaging shell is provided with small holes;

and step 3: and (3) sealing and plugging the hole reversely: the upper surface of the top surface of the packaging shell is attached to an inverted mold with epoxy resin, and after heating, the epoxy resin is extruded into the cavity of the packaging shell through the small holes and blocks the small holes, so that a product with the holes blocked is obtained;

and 4, step 4: and (3) curing: curing the product to cure the epoxy resin in the cavity and the small hole of the packaging shell;

and 5: laser printing: laser printing is carried out on the product according to the requirement so as to facilitate identification;

step 6: cutting: the product is cut into individual finished products by a cutting machine.

Preferably, the step 3 of inversely blocking the hole specifically includes the following steps:

(1) putting the semi-finished product in the step 2 into an upper die of a flip-chip die in a vacuum oven;

(2) putting epoxy resin powder into a bearing disc of the lower die;

(3) vacuumizing to form a certain vacuum degree in the oven;

(4) rapidly heating the oven until the epoxy resin powder is melted;

(5) the lower die is jacked up to enable the melted epoxy resin to slowly press the upper surface of the top surface of the packaging shell 20;

(6) maintaining the pressure for a period of time, so that the epoxy resin fully flows into the inner cavity of the product and is cured to form an epoxy resin layer;

(7) releasing vacuum, opening the mold and taking out the product;

(8) cleaning the upper film, the bearing disc and the lower die for later use.

Preferably, the depth of the epoxy resin powder in the bearing disc is not more than 0.3mm, the vacuum degree in the oven reaches 0.1-0.15MPa, the temperature in the oven reaches 160-180 ℃, the pressure maintaining time is 25-35S, and the epoxy resin layer with the thickness of 0.1-0.15mm is formed on the inner wall of the top surface of the packaging shell.

Preferably, the vacuum degree in the oven reaches 0.1MPa, the temperature in the oven reaches 170 ℃, the pressure maintaining time is 30S, and the epoxy resin layer with the thickness of 0.1mm is formed on the inner wall of the top surface of the packaging shell.

Preferably, in the step 4, the product is cured for 8-10h, and after the product is cured, the product is polished to remove the thin epoxy resin layer on the outer surface of the package housing.

Preferably, in step 1, the chipset includes two chips, which are respectively defined as a first chip and a second chip, where the first chip is an ASIC chip, and the second chip is an MEMS chip.

Preferably, the step 1 specifically comprises the following steps:

(1) applying a patch adhesive to the substrate by using a patch machine to form a patch adhesive layer, and attaching the bottom surface of the first chip to the patch adhesive layer;

(2) applying a patch adhesive to the top surface of the first chip by using a patch machine to form a patch adhesive layer, and bonding the bottom surface of the second chip on the patch adhesive layer;

(3) baking the product obtained in the step (2) to solidify the surface mount adhesive layer, and electrically connecting the first chip and the second chip and the substrate through gold wires;

wherein, the patch adhesive is a DAF film.

Preferably, in step 2, the package housing is a metal cap, the package housing and the substrate enclose to form an accommodating cavity, and the chipset and the gold wire are disposed in the accommodating cavity.

The invention has the beneficial effects that:

1) the packaging shell adopts the traditional metal cap with a small hole at the top, the influence of stress generated by combining various materials is overcome by utilizing the metal cap for packaging, the mature design of the small hole of the metal cap process does not need to change the original design, the small hole is wrapped by epoxy resin to ensure that the inside of a product cavity is thoroughly isolated from the outside, and the influence of the outside temperature, pressure and the like on the stability of the product is avoided;

2) because the inverted hole plugging adopts a vacuum process, the situation that the gas in the cavity expands to cause explosion can not occur when the product after hole plugging uses high-temperature reflux in the next procedure; the overall dimension of the product after hole plugging is not increased at all, and the plastic packaging material is a mature epoxy resin material and uses few materials, so that the plastic packaging cost is extremely low, the product packaging cost is saved, and the competitiveness of the product is not influenced.

Drawings

FIG. 1 is a schematic view of the structure of the product after plugging the hole according to the present invention;

FIG. 2 is a schematic diagram of a chip set and a substrate after being mounted;

FIG. 3 is a schematic view of the structure of FIG. 2 after solder paste is applied;

FIG. 4 is a cross-sectional view of a package cover in accordance with the present invention;

FIG. 5 is a schematic structural view of a semi-finished product according to the present invention;

in the figure: 10-substrate, 11-first chip, 12-second chip, 13-gold wire, 14-solder paste, 15-patch adhesive layer, 20-packaging shell, 21-small hole and 22-epoxy resin layer.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the terms "first," "second," and the like in the description and claims of this application and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

Spatially relative terms, such as "above … …," "above … …," "above … …," "above," and the like, may be used herein for ease of description to describe one device or feature's spatial relationship to another device or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if a device in the figures is turned over, devices described as "above" or "on" other devices or configurations would then be oriented "below" or "under" the other devices or configurations. Thus, the exemplary term "above … …" can include both an orientation of "above … …" and "below … …". The device may be otherwise variously oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

Example (b): as shown in fig. 1-5, a MEMS packaging method includes the steps of:

step 1: assembling: as shown in fig. 2, the chip assembly is mounted on the substrate 10, and after baking, the gold wire 13 is connected between the chip assembly and the substrate 10 by bonding;

step 2: drawing solder paste and a cover cap: the method comprises the following steps of spot-coating solder paste 14 on copper foil on the periphery of a substrate as shown in fig. 3, covering a packaging shell 20 shown in fig. 4 on the solder paste 14 of the substrate, and melting the solder paste through reflow soldering to weld the packaging shell 20 and the substrate 10 to obtain a semi-finished product, wherein the top surface of the packaging shell is provided with small holes 21;

and step 3: and (3) sealing and plugging the hole reversely: attaching the upper surface of the top surface of the packaging shell to an inverted mold containing epoxy resin, heating, extruding the epoxy resin into the cavity of the packaging shell through the small holes 21 and blocking the small holes to obtain a product after hole blocking, as shown in fig. 5;

and 4, step 4: and (3) curing: curing the product to cure the epoxy resin in the cavity of the package housing 20 and in the small hole 21;

and 5: laser printing: laser printing is carried out on the product according to the requirement so as to facilitate identification;

step 6: cutting: the product is cut into individual finished products by a cutting machine. In the packaging method, the packaging shell still adopts a traditional metal cap with a small hole at the top, and after the packaging shell is welded on a substrate, a process of reversely plugging the hole is added, namely, the traditional epoxy resin plastic packaging material is extruded into the packaging shell through the small hole under the vacuumizing condition, the inner cavity of the packaging shell forms a resin layer about 0.1mm after high-temperature heat preservation, and the small hole is filled with resin, and then post-curing treatment is carried out, so that the purpose of plugging the small hole is achieved.

The step 3 of inversely plugging the hole specifically comprises the following steps:

(1) putting the semi-finished product in the step 2 into an upper die of a flip-chip die in a vacuum oven;

(2) putting epoxy resin powder into a bearing disc of the lower die;

(3) vacuumizing to form a certain vacuum degree in the oven;

(4) rapidly heating the oven until the epoxy resin powder is melted;

(5) the lower die is jacked up to enable the melted epoxy resin to slowly press the upper surface of the top surface of the packaging shell 20;

(6) after maintaining the pressure for a period of time, the epoxy resin fully flows into the inner cavity of the product and is cured to form an epoxy resin layer 22;

(7) releasing vacuum, opening the mold and taking out the product;

(8) cleaning the upper film, the bearing disc and the lower die for later use.

The depth of the epoxy resin powder in the bearing disc is not more than 0.3mm, the vacuum degree in the oven reaches 0.1-0.15MPa, the temperature in the oven reaches 160-180 ℃, the pressure maintaining time is 25-35S, and the epoxy resin layer 22 with the thickness of 0.1-0.15mm is formed on the inner wall of the top surface of the packaging shell 20. After the epoxy resin flows into the packaging shell through the small holes 21, an epoxy resin layer with the thickness of 0.1mm is formed on the inner wall of the top surface of the packaging shell 20 above the chip group, and the small holes are filled with the epoxy resin, so that the purpose of sealing the small holes is achieved.

The vacuum degree in the oven reaches 0.1MPa, the temperature in the oven reaches 170 ℃, the pressure maintaining time is 30S, and the epoxy resin layer 22 with the thickness of 0.1mm is formed on the inner wall of the top surface of the packaging shell 20. The best plugging effect can be achieved by utilizing the process conditions.

In the step 4, the curing time of the product is 8-10h, and after the product is cured, the product is polished to remove the thin epoxy resin layer on the outer surface of the packaging shell. After the hole is reversely sealed and blocked by the product, the product needs to be post-cured for about 8 hours like a conventional plastic package product, so that the epoxy resin fully completes the crosslinking reaction, the bonding strength with the small hole is enhanced, and after the curing, the product can be polished and then subjected to laser printing.

In step 1, the chip set includes two chips, which are respectively defined as a first chip 11 and a second chip 12, where the first chip 11 is an ASIC chip, and the second chip 12 is an MEMS chip. The MEMS chip can convert external physical and chemical signals into electric signals, and the ASIC chip further processes and transmits the electric signals generated by the MEMS chip to a next-stage circuit; the MEMS sensor is formed by packaging an MEMS chip and an application specific integrated circuit chip (ASIC chip) together, namely, the MEMS sensor is manufactured by the process.

The step 1 specifically comprises the following steps:

(1) applying a patch adhesive to the substrate by using a patch machine to form a patch adhesive layer 15, and attaching the bottom surface of the first chip 11 to the patch adhesive layer;

(2) applying a patch adhesive to the top surface of the first chip 11 by using a chip mounter to form a patch adhesive layer 15, and bonding the bottom surface of the second chip 12 to the patch adhesive layer;

(3) baking the product obtained in the step (2) to solidify the surface mount adhesive layer, and electrically connecting the first chip and the second chip and the substrate through gold wires;

wherein, the patch adhesive is a DAF film. The DAF film material is a thermosetting material, generally has no conductivity, is a high-molecular colloid material with adhesive on two sides at normal temperature, can be irreversibly cured when the temperature reaches the glass transition temperature, is generally not higher than 200 ℃, and can ensure the stability of the material for bonding two sides of the DAF after curing. In the invention, the DAF film is used for mounting, so that silver paste does not overflow around the chip during mounting.

In step 2, the package housing 20 is a metal cap, and the package housing and the substrate 10 enclose to form an accommodating cavity, and the chipset and the gold wire are disposed in the accommodating cavity. In the process, the packaging shell and the substrate are welded together through the solder paste, the purpose of chip packaging is realized, the packaging shell 20 plays a role in isolation and shielding, so that impurities in the air are prevented from corroding a circuit of a packaged chip, and meanwhile, the packaged chip module is convenient to mount and transport, wherein the solder paste is a welding material, generally the solder paste is formed by mixing solder powder, soldering flux and other auxiliaries, the solder paste has certain viscosity at normal temperature, electronic components can be adhered to preset positions, and at high welding temperature, solvents and partial auxiliaries in the solder paste volatilize and are welded together for a long time.

It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (8)

1. A MEMS packaging method, comprising: the method comprises the following steps:

step 1: assembling: the chip set is attached to the substrate (10), and the gold wire (13) is connected between the chip set and the substrate (10) in a bonding mode after baking;

step 2: drawing solder paste and a cover cap: point-coating solder paste (14) on copper foil on the periphery of a substrate, covering a packaging shell (20) on the solder paste (14) of the substrate, melting the solder paste through reflow soldering, and welding the packaging shell (20) and the substrate (10) to obtain a semi-finished product, wherein the top surface of the packaging shell is provided with small holes (21);

and step 3: and (3) sealing and plugging the hole reversely: the upper surface of the top surface of the packaging shell is attached to an inverted mold with epoxy resin, and after heating, the epoxy resin is extruded into the cavity of the packaging shell through the small hole (21) and blocks the small hole, so that a product with the blocked hole is obtained;

and 4, step 4: and (3) curing: curing the product to cure the epoxy resin in the cavity of the packaging shell (20) and in the small hole (21);

and 5: laser printing: laser printing is carried out on the product according to the requirement so as to facilitate identification;

step 6: cutting: the product is cut into individual finished products by a cutting machine.

2. The MEMS packaging method of claim 1, wherein: the step 3 of inversely plugging the hole specifically comprises the following steps:

(1) putting the semi-finished product in the step 2 into an upper die of a flip-chip die in a vacuum oven;

(2) putting epoxy resin powder into a bearing disc of the lower die;

(3) vacuumizing to form a certain vacuum degree in the oven;

(4) rapidly heating the oven until the epoxy resin powder is melted;

(5) the lower die is jacked up, and the melted epoxy resin is slowly pressed on the upper surface of the top surface of the packaging shell (20);

(6) after maintaining the pressure for a period of time, the epoxy resin fully flows into the inner cavity of the product and is cured to form an epoxy resin layer (22);

(7) releasing vacuum, opening the mold and taking out the product;

(8) cleaning the upper film, the bearing disc and the lower die for later use.

3. The MEMS packaging method of claim 2, wherein: the depth of the epoxy resin powder in the bearing disc is not more than 0.3mm, the vacuum degree in the oven reaches 0.1-0.15MPa, the temperature in the oven reaches 160-180 ℃, the pressure maintaining time is 25-35S, and the epoxy resin layer (22) with the thickness of 0.1-0.15mm is formed on the inner wall of the top surface of the packaging shell (20).

4. The MEMS packaging method of claim 3, wherein: the vacuum degree in the oven reaches 0.1MPa, the temperature in the oven reaches 170 ℃, the pressure maintaining time is 30S, and the epoxy resin layer (22) with the thickness of 0.1mm is formed on the inner wall of the top surface of the packaging shell (20).

5. The MEMS packaging method of claim 2, wherein: in the step 4, the curing time of the product is 8-10h, and after the product is cured, the product is polished to remove the thin epoxy resin layer on the outer surface of the packaging shell.

6. The MEMS packaging method of claim 1, wherein: in the step 1, the chipset includes two chips, which are respectively defined as a first chip (11) and a second chip (12), where the first chip (11) is an ASIC chip, and the second chip (12) is an MEMS chip.

7. The MEMS packaging method of claim 6, wherein: the step 1 specifically comprises the following steps:

(1) applying a patch adhesive to the substrate by using a patch machine to form a patch adhesive layer (15), and attaching the bottom surface of the first chip (11) to the patch adhesive layer;

(2) applying a patch adhesive to the top surface of the first chip (11) by using a patch machine to form a patch adhesive layer (15), and bonding the bottom surface of the second chip (12) on the patch adhesive layer;

(3) baking the product obtained in the step (2) to solidify the surface mount adhesive layer, and electrically connecting the first chip and the second chip and the substrate through gold wires;

wherein, the patch adhesive is a DAF film.

8. The MEMS packaging method of claim 1, wherein: in the step 2, the packaging shell (20) is a metal cap, the packaging shell and the substrate (10) enclose to form a containing cavity, and the chipset and the gold wire are arranged in the containing cavity.

Images