CN113242685A

CN113242685A - Air-tight magnetic memory packaging structure and preparation method thereof

Info

Publication number: CN113242685A
Application number: CN202110541920.4A
Authority: CN
Inventors: 丁荣峥; 朱玲华; 王超
Original assignee: CETC 58 Research Institute
Current assignee: CETC 58 Research Institute
Priority date: 2021-05-18
Filing date: 2021-05-18
Publication date: 2021-08-10

Abstract

The invention relates to the technical field of electronic packaging, in particular to an airtight magnetic memory packaging structure and a preparation method thereof. MRAM chip is installed on the bottom plate in the core cavity of the ceramic shell through adhesive, the bonding wire is used for interconnecting the pressure welding point of the MRAM chip and the bonding finger of the ceramic shell, then the magnetic shielding layer is covered above the MRAM chip and the bonding wire, the magnetic shielding layer is welded on the bottom plate in the core cavity of the ceramic shell, and finally the sealing ring and the cover plate of the ceramic shell are sealed in an airtight mode. The invention does not change the size and the air tightness of the external structure of the existing ceramic package, solves the problem that the ceramic package can not provide effective shielding for radiation (such as EMI and RFI), and improves the reliability of the magnetic memory.

Description

Air-tight magnetic memory packaging structure and preparation method thereof

Technical Field

The invention relates to the technical field of electronic packaging, in particular to an airtight magnetic memory packaging structure and a preparation method thereof.

Background

The prior magnetic memories all adopt plastic packages (such as PSOP44, etc.), and the MRAM chip is mounted on the middle island of the iron-nickel lead frame, and a flexible magnetic shielding or soft magnetic alloy sheet is pasted on the front surface of the MRAM chip, so that the effective shielding problem of the magnetic memory to radiation (such as EMI and RFI) is improved.

With the expansion of the application range of the magnetic memory, the reliability of the plastic packaging product in a humid environment and a space environment with low vacuum degree cannot be guaranteed, for example, the reliability of the product is affected by electric leakage and corrosion in the high humidity environment, expansion in the low vacuum degree and the like, and the problems are not accepted by the application. At present, ceramic packaging does not have magnetic shielding, and an effective solution is not provided.

Disclosure of Invention

Aiming at the defects of the prior art, the technical problem to be solved by the invention is to seal the MRAM chip in the magnetic shielding body under the condition of not changing the external dimension of the ceramic package and ensuring the air tightness of the ceramic package, thereby solving the radiation interference problems of EMI, RFI and the like and improving the reliability of the magnetic memory.

The invention is realized by the following technical scheme:

a hermetic magnetic memory package structure, the package structure comprising: MRAM chip, adhesive, bonding wire, magnetic shielding layer, ceramic shell and cover plate;

the ceramic shell comprises: the ceramic body, the bottom plate, the bonding fingers, the sealing ring and the leading-out terminals (pins);

the bottom plate is brazed on the ceramic body, the MRAM chip is mounted on the bottom plate through the adhesive, the bonding wire is used for interconnecting the pressure welding point of the MRAM chip and the bonding finger, a magnetic shielding layer is arranged above the MRAM chip and the bonding wire and fixed on the bottom plate, and the sealing ring and the cover plate are welded to form an airtight sealing structure. The airtight sealing structure formed by the ceramic shell and the cover plate ensures that the magnetic memory can stably work in severe environment for a long time.

Preferably, the bottom plate, the sealing ring, the leading-out end and the cover plate of the ceramic shell are all made of iron-nickel base alloy soft magnetic materials. The core cavity of the ceramic shell adopts a through cavity structure, the substrate of the core cavity is changed from ceramic into a soft magnetic alloy (such as 4J42 iron-nickel alloy) bottom plate matched with the thermal expansion coefficient of the ceramic material, the bottom plate is connected with the ceramic shell through high-temperature brazing, and the bottom plate is a part of a magnetic shielding structure.

Preferably, the magnetism shielding layer is made for the iron-nickel base soft magnetic alloy material of high initial permeability, low coercive force, just the magnetism shielding layer is the setting of cap shape structure, and its size ratio the MRAM chip is big, will the MRAM chip cover is established in the magnetism shielding layer. The magnetic shielding layer has a certain gap with the chip and the bonding wire, and two ends of the magnetic shielding layer are tightly attached to the bottom plate and are welded and fixed by resistance welding and the like.

Preferably, the magnetic shielding layer and the bottom plate are directly welded by resistance welding, and the MRAM chip is located in the middle between the bottom plate and the magnetic shielding layer.

Preferably, the MRAM chip, the adhesive, the bonding wire, and the magnetic shielding layer are all located in a sealed cavity of the ceramic housing, and the sealed cavity is formed by an inner cavity enclosed among the ceramic body, the bottom plate, the sealing ring, and the cover plate.

Preferably, the ceramic body is respectively brazed with the bottom plate and the sealing ring through silver-copper solders; the sealing ring and the cover plate are hermetically sealed through a sealing process, wherein the sealing process includes, but is not limited to, fusion sealing by using alloy solder, parallel seam welding or laser welding.

The invention also provides another technical scheme: the packaging structure is prepared by using a preparation method of the airtight magnetic memory packaging structure, and the preparation method comprises the following steps:

s1: firstly, preparing a ceramic shell, a magnetic shielding layer and a cover plate;

the ceramic body is manufactured by high-temperature co-firing of alumina ceramic with the content of not less than 90% and tungsten, and is of a through cavity structure;

a 4J42 bottom plate with the thickness of 0.50mm, a 4J42 sealing ring with the thickness of 0.40mm and a leading-out end of 4J42 with the thickness of 0.20mm are brazed on a ceramic body through silver-copper solder, nickel with the thickness of more than 1.30 mu m and gold with the thickness of more than 0.30 mu m are electroplated to form a ceramic shell;

the magnetic shielding layer is in a n-shaped cap structure formed by machining 1J79 soft magnetic alloy with the thickness of 0.10-0.20 mm, the depth of an inner cavity of the magnetic shielding layer is 0.20mm higher than that of the bonding wire, and the size of the magnetic shielding layer is 0.50-1.00 mm larger than that of the MRAM chip;

the cover plate with the thickness of 0.10mm is punched from a 4J42 flat plate with the thickness of 0.10mm, and is electroplated with nickel with the thickness of more than 1.30 mu m, gold with the thickness of more than 0.30 mu m or a nickel-phosphorus layer with the thickness of more than 1.30 mu m;

s2: then, the MRAM chip is adhered to the center of the bottom plate by using JM7000 adhesive and is cured at the high temperature of 200-300 ℃ for 0.5-2 h; then, gold wires with the diameter of 20mm, 22 mm, 25 mm, 28 mm or 30 mm are used for bonding and interconnecting the pressure welding points and the bonding fingers;

s3: then, aligning and buckling the magnetic shielding layer at the center of the bottom plate, and performing spot welding on two sides by using a resistance welding machine and the like to tightly fix the magnetic shielding layer and the bottom plate;

s4: and finally, sealing the cover plate and the sealing ring by a parallel seam welder to obtain the sealing structure with the MRAM chip, the adhesive, the bonding wire and the magnetic shielding layer arranged in the ceramic shell.

The invention has the beneficial effects that:

the magnetic shield with high initial permeability and low coercive force is covered above the MRAM chip and the bonding lead and is welded on the bottom plate of the ceramic shell core cavity in a spot mode, the bottom plate and the magnetic shield provide a complete magnetic shield structure for the MRAM chip, the overall size of ceramic packaging is not changed, the air tightness is guaranteed, and the environment interference resistance and the reliability of the MRAM chip are guaranteed.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a diagram of the ceramic enclosure of the hermetically sealed magnetic memory CSOP44 of the present invention;

FIG. 2 is a diagram of the hermetic magnetic memory MRAM chip bonding and bonding of the present invention;

FIG. 3 is a diagram of the assembly of magnetic shields on the hermetic magnetic memory MRAM chip of the present invention;

FIG. 4 is a top view of the hermetically sealed magnetic memory of the present invention;

FIG. 5 is a bottom view of the hermetically sealed magnetic memory of the present invention;

FIG. 6 is a cross-sectional view of the hermetically sealed magnetic memory of the present invention.

In the figure: 1-MRAM chip; 2-a binder; 3-a bonding wire; 4-magnetic shielding; 5-a ceramic housing; 51-a ceramic body; 52-a base plate; a 53-bonding finger; 54-a sealing ring; 55-out (pin); 56-silver copper solder; 6-cover plate.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. 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.

Example 1:

as shown in fig. 1 to 6, there is a hermetically sealed magnetic memory package structure (single cavity structure) of preferred embodiment 1 of the present invention, including: MRAM chip 1, pressure welding point, adhesive 2, bonding wire 3, magnetic shielding layer 4, ceramic shell 5, ceramic body 51, bottom plate 52, bonding finger 53, sealing ring 54, and leading-out terminal (pin) 55. The MRAM chip 1 is mounted on the bottom plate 52 of the ceramic case 5 by an adhesive 2; the pressure welding point of the MRAM chip 1 is connected with the bonding finger 53 of the ceramic shell 5 in a bonding way through the bonding wire 3; covering the MRAM chip 1 and the bonding wire 3 with the magnetic shielding layer 4, and fixing the magnetic shielding layer 4 and the bottom plate 52 by resistance welding; finally, the cover plate 6 is seam welded to the sealing ring 54 by means of a parallel seam welding machine to form a gas-tight seal.

In order to facilitate understanding of the above technical solution of the present invention, the present invention further provides another technical solution: the preparation method of the airtight magnetic memory packaging structure is used for preparing the packaging structure:

when the CSOP44 packaging structure is used specifically, the air-tight magnetic memory with the 0.80mm pitch only packages 1 MRAM chip, and the pressure welding points of the MRAM chip 1 are arranged on two sides, specifically as follows:

s1: first, the ceramic case 5, the magnetic shield layer 4, and the cover plate 6 are prepared. The ceramic body 51 is made of alumina ceramic with the content of not less than 90% and tungsten through high-temperature co-firing and is of a through cavity structure; A4J 42 bottom plate 52 with a thickness of 0.50mm, a 4J42 sealing ring 54 with a thickness of 0.40mm, and a lead-out terminal (pin) 55 of 4J42 with a thickness of 0.20mm are soldered on a ceramic body 51 by silver-copper solder 56, and are plated with nickel with a thickness of 1.30 μm or more and gold with a thickness of 0.30 μm or more to form a ceramic case 5. The magnetic shielding layer 4 is in a II-cap shape by machining 1J79 soft magnetic alloy with the thickness of 0.10-0.20 mm, the depth of an inner cavity of the magnetic shielding layer 4 is about 0.20mm higher than that of the bonding wire 3, and the size of the magnetic shielding layer is about 0.50-1.00 mm larger than that of the MRAM chip. The 0.10mm thick cover plate is punched from a 0.10mm thick 4J42 flat plate and is plated with nickel of a thickness of 1.30 μm or more, gold of a thickness of 0.30 μm or more, or a nickel-phosphorus layer of a thickness of 1.30 μm or more.

S2: then, the MRAM chip 1 is adhered to the center of the base plate 52 with an adhesive JM7000 or the like, and cured at a high temperature of 200 to 300 ℃ for 0.5 to 2 hours; and then, a gold wire with the diameter of about 25 mu m is used for bonding and interconnecting the chip bonding point and the bonding finger 53.

S3: then, the magnetic shield layer 4 is aligned and fastened to the center of the bottom plate 52, and the magnetic shield layer 4 and the bottom plate 52 are tightly fixed by spot welding 3 spots or more on both sides with a resistance welder or the like.

S4: finally, the cover plate 6 and the sealing ring 54 of the ceramic case 5 are sealed by a parallel seam welder to obtain a sealing structure in which the MRAM chip 1, the adhesive 2, the bonding wire 3 and the magnetic shielding layer 4 are arranged in the ceramic case 5.

In summary, according to the above technical solution of the present invention, the substrate of the core cavity of the ceramic case is changed from ceramic to a soft magnetic alloy material, and a suspended magnetic shield is added on the magnetic memory chip and fixed, so as to form a cavity capable of effectively shielding radiation (such as EMI and RFI), thereby improving reliability of the magnetic memory.

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. A hermetically sealed magnetic memory package, the package comprising: the magnetic shielding device comprises an MRAM chip (1), an adhesive (2), a bonding wire (3), a magnetic shielding layer (4), a ceramic shell (5) and a cover plate (6);

the ceramic shell (5) comprises thereon: the ceramic body (51), the bottom plate (52), the bonding finger (53), the sealing ring (54) and the leading-out terminal (55);

the bottom plate (52) is brazed on the ceramic body (51), the MRAM chip (1) is mounted on the bottom plate (52) through the adhesive (2), the bonding wire (3) is adopted to interconnect the pressure welding point of the MRAM chip (1) and the bonding finger (53), a magnetic shielding layer (4) is arranged above the MRAM chip (1) and the bonding wire (3), the magnetic shielding layer (4) is fixed on the bottom plate (52), and the sealing ring (54) is welded with the cover plate (6) to form an airtight sealing structure.

2. The hermetically sealed magnetic memory package of claim 1, wherein the base plate (52), the sealing ring (54), the terminals (55), and the lid plate (6) of the ceramic package (5) are all made of a soft magnetic material of an iron-nickel based alloy.

3. A hermetic magnetic memory package according to claim 2, wherein the magnetic shielding layer (4) is made of a soft ferromagnetic alloy material with high initial permeability and low coercivity, and the magnetic shielding layer (4) is in a cap structure with a size larger than that of the MRAM chip (1), and the MRAM chip (1) is covered in the magnetic shielding layer (4).

4. A hermetic magnetic memory package according to claim 3, characterized in that the magnetic shield layer (4) is directly welded to the base plate (52) by means of resistance welding, while the MRAM chip (1) is located in the middle between the base plate (52) and the magnetic shield layer (4).

5. A hermetic magnetic memory package according to claim 4, characterized in that the MRAM chip (1), the adhesive (2), the bonding wire (3) and the magnetic shielding layer (4) are all located in a sealed cavity of the ceramic housing (5), which is formed by the enclosed inner cavity between the ceramic body (51), the bottom plate (52), the sealing ring (54) and the cover plate (6).

6. A hermetically sealed magnetic memory package in accordance with claim 5, characterized in that the ceramic body (51) is soldered to the base plate (52) and the seal ring (54) by means of silver-copper solder (56); the sealing ring (54) and the cover plate (6) are hermetically sealed by a sealing process, wherein the sealing process includes, but is not limited to, welding with alloy solder, parallel seam welding or laser welding.

7. The method for manufacturing the package structure of any one of claims 1 to 6, using a hermetic magnetic memory package structure, is characterized in that the method comprises:

s1: firstly, preparing a ceramic shell (5), a magnetic shielding layer (4) and a cover plate (6);

the ceramic body (51) is manufactured by high-temperature co-firing of alumina ceramic with the content of not less than 90% and tungsten and is of a through cavity structure;

a 4J42 bottom plate (52) with the thickness of 0.50mm, a 4J42 sealing ring (54) with the thickness of 0.40mm and a leading-out terminal (55) with the thickness of 0.20mm and 4J42 are brazed on a ceramic body (51) through silver-copper solder (56), and nickel with the thickness of more than 1.30 mu m and gold with the thickness of more than 0.30 mu m are electroplated to form a ceramic shell (5);

the magnetic shielding layer (4) is in a n-shaped cap structure formed by machining 1J79 soft magnetic alloy with the thickness of 0.10-0.20 mm, the depth of an inner cavity of the magnetic shielding layer (4) is 0.20mm higher than that of the bonding wire (3), and the size of the magnetic shielding layer is 0.50-1.00 mm larger than that of the MRAM chip;

the cover plate (6) with the thickness of 0.10mm is punched from a 4J42 flat plate with the thickness of 0.10mm, and is electroplated with nickel with the thickness of more than 1.30 mu m, gold with the thickness of more than 0.30 mu m or a nickel-phosphorus layer with the thickness of more than 1.30 mu m;

s2: then, the MRAM chip (1) is adhered to the center of the base plate (52) by using JM7000 adhesive (2), and is cured at the high temperature of 200-300 ℃ for 0.5-2 h; then bonding and interconnecting the pressure welding points and the bonding fingers (53) by gold wires with the diameter of 20, 22, 25, 28 or 30 mu m;

s3: then, aligning and buckling the magnetic shielding layer (4) at the center of the bottom plate (52), and performing spot welding on two sides of a resistance welding machine to tightly fix the magnetic shielding layer (4) and the bottom plate (52);

s4: and finally, sealing the cover plate (6) and the sealing ring (54) by a parallel seam welder to obtain a sealing structure with the MRAM chip (1), the adhesive (2), the bonding wire (3) and the magnetic shielding layer (4) arranged in the ceramic shell (5).