RU2469063C1 - Method of producing sealed electronic module and adhesive composition for realising said method - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: method of producing a sealed electronic module involves forming a housing with a vertical protrusion on the outer perimetre of the upper surface of the side walls of the housing, placing electronic components inside the housing, placing a cover on the housing, fixing said cover to the housing with screws, filling the working clearance between the cover and the housing with an epoxy resin-based adhesive composition and drying the module until the adhesive composition completely solidifies. The method involves formation of a cover with a bevel edge on the perimetre of the outer upper side and dimensions which enable the end face of the cover before the surface of the bevel edge to rest on the inner surface of the vertical protrusion with formation of a working clearance between the surface of the bevel edge and the inner surface of the vertical protrusion. After solidification of the adhesive composition, the surface of the solid adhesive composition is covered with a sublayer consisting of a mixture of polybutyl titanate, ethyl silicate-32 and white spirit, with the following ratio of components, pts.wt: polybutyl titanate 36-40, ethyl silicate-32 202-206, white spirit 756-760; and then held until complete evaporation of white spirit. The working clearance is then filled with an organosilicon sealant and dried until complete polymerisation thereof, wherein the epoxy resin-based adhesive composition contains modified K-139 epoxy resin, UP-0633M amine curing agent, boron nitride and chromium (III) oxide, with the following ratio of components, pts.wt: modified epoxy resin 594-596, amine curing agent 88-90, BN 296-300, CrO16-20.EFFECT: sealed electronic module housing is obtained, which is suitable for protecting on-board radio electronic equipment from the destabilising effect of the environment for a long period of time.2 cl, 2 dwg, 1 tbl

Description

The invention relates to electronics, and in particular to methods of manufacturing sealed electronic modules, and can be used in the design of sealed electronic modules, in particular used in on-board electronic equipment (REA).

One of the main requirements in the design of REA is to ensure the protection of its elements from mechanical damage and the negative effects of the environment: moisture, mold, dust, sand and dirt. To solve this problem, REA sealing is used, which is carried out by enveloping, filling or placing REA in a hollow body. Envelopment consists in the formation of integument shells on the surface of CEA, designed for short-term operation in conditions of exposure to moisture. When sealing by filling, the free space between the electronic components and the wall of the protective housing is filled with insulating material. Products without housing are poured in a special form. However, enveloping and pouring does not replace full sealing. REA is completely sealed by placing electronic components inside a hollow, most often metal, case, which is then covered with a lid and the joint of the lid and the case is sealed.

In addition to protection from environmental influences and mechanical damage, additional requirements are imposed on the onboard REA sealing. The design of the airborne REA modules to be sealed must provide free access to the REA elements to reduce the time for troubleshooting during periodic inspections and checks. This implies the requirement of high maintainability of the electronic module of the onboard REA. Its use in various climatic regions dictates the requirement to maintain the tightness of the module in a wide temperature range: from + 50 ° C to -50 ° C. Significant vibration, shock and linear overloads increase the strength requirements of the protective housing of the onboard REA. A particularly vulnerable place for such modules is the joint of the cover and the housing.

Known methods for the manufacture of electronic modules with detachable sealing of the cover and housing [Gell PP, Ivanov-Esipovich N.K. Design of electronic equipment. - L .: Energy, 1972, p.136-137]. These include the manufacture of a housing and cover with a flange connection, the placement of electronic components in the housing, which is then covered with a cover provided with gaskets. The latter are able to deform and take the form of joint surfaces to ensure a tight connection between the cover and the body. Such methods of manufacturing sealed electronic modules provide the ability to quickly and easily replace components during repair, adjustment or adjustment. After carrying out the necessary manipulations, the housing is re-sealed using the same gasket without involving additional materials. Most often, rubber or plastic metal gaskets are used for these purposes.

However, the use of rubber gaskets is accompanied by a number of disadvantages. The temperature coefficient of linear expansion (TEC) of rubber is 40 times higher than that of steel, which, when a closed unit is heated, can lead to the destruction of a thin-walled structure or to mechanical stresses of rubber. As a result of the tendency of rubber to weld with a metal surface under strong continuous pressure, the sealed units open with great difficulty after a few months, the gasket breaks in places, but does not separate from the metal, because adhesion forces exceed cohesive forces. In addition, the gasket does not eliminate the presence of irregularities or deviations from flatness on the contact surfaces, which may lead to the appearance of local zones of insufficient contact pressure.

The use of ductile metal gaskets also has its drawbacks. Sealing due to plastic deformation of metal gaskets does not always lead to reliable sealing. For example, copper rings with teeth have a large LTEC, which is why they are additionally crimped in the seal when heated. When this process is repeated many times, the seal is broken due to shrinkage as a result of metal hardening. The service life of such a seal is reduced when exposed to vibration, which makes the use of electronic modules manufactured by this method unsuitable for on-board CEA.

The inseparable connection of the seams of the metal case of the electronic module does not provide easy access to the contents of the case without the use of special devices, however, it has a longer time for maintaining the module tightness, better resistance to vibration loads and a wider operating temperature range, which is important for the on-board CEA.

Known methods of manufacturing a sealed electronic module according to patents RU No. 2072124, 2155462, in which the housing is made with a vertical protrusion around the perimeter of the housing in the upper part of the side walls. When the lid is placed in the housing between the end surface of the lid and the inner surface of the vertical protrusion, a working gap is formed, which is sealed by soldering, having previously placed a wire in it for the possibility of depressurization of the electronic module.

These methods have a common disadvantage due to the use of soldering to seal the joint of the lid and the case, which requires heating the case to the melting point of the solder, which can lead to the soldering of electronic components placed in the case, and restrictions on the choice of solders and their combinations. In addition, with repeated repetition of sealing, leakage of solder under the lid occurs, which leads to hardening of the connection between the lid and the housing and significantly complicates the subsequent depressurization. The operation of sealing-depressurization of such modules can be carried out no more than 5 times.

Sealed electronic modules manufactured using sealing with compounds have the greatest maintainability. A viscous flowing compound fills all bumps and gaps, providing reliable sealing.

Closest to the claimed method of manufacturing a sealed electronic module is a method [Gell PP, Ivanov-Esipovich N.K. Design of electronic equipment. - L .: Energy, 1972, p.138], including the manufacture of the cover and the housing, the placement of electronic components in the housing, the placement of the cover in the housing and the filling of the joint of the housing and the end surface of the cover with a compound.

However, with sudden changes in temperature due to the expansion and contraction of the metal case, the compound may crack and crumble, thereby violating the tightness of the module.

The task of the invention is to increase the effectiveness of sealing while maintaining high maintainability.

The essence of the proposed method of manufacturing a sealed electronic module is that in a method comprising forming a housing with a vertical protrusion along the outer perimeter of the upper surface of the side walls of the housing, placing electronic components inside the housing, placing the lid in the housing, fixing it with screws to the housing, filling the working gap between the lid and the body of the epoxy-based adhesive composition and drying the module until the adhesive composition is fully cured; forming a lid with a chamfer around the perimeter of the outer upper side and dimensions ensuring that the end surface of the lid fits to the chamfer surface to the inner surface of the vertical protrusion with the formation of a working gap between the chamfer surface and the inner surface of the vertical protrusion; after curing the adhesive composition, the surface of the cured adhesive composition is covered with a sublayer consisting of a mixture of polybutyl titanate, ethyl silicate-32 and white spirit in the following ratio, wt.h:

polybutyl titanate 36-40 ethyl silicate-32 202-206 White Spirit 756-760

and maintained until the white spirit evaporates, then the working gap is filled with silicone sealant and dried until it is fully polymerized, while the adhesive composition based on epoxy resin contains a modified K-139 epoxy resin, UP-0633M amine hardener, boron nitride and chromium ( III) oxide in the following ratio of components, parts by weight:

modified epoxy resin 594-596 amine hardener 88-90 Bn 296-300 Cr ₂ O ₃ 16-20.

In addition, the claimed method, in which, along with the above features, the housing and the cover are performed in accordance with the following ratios:

where h is the height of the end surface of the cover to the surface of the bevel; H is the thickness of the cover; d is the thickness of the vertical protrusion; D is the wall thickness of the body, which is chosen equal to 4-8 mm

The technical result of the proposed method is to solve the problem by applying a layer of silicone sealant on top of the adhesive layer formed by the cured adhesive composition. Due to its elastic structure, the sealant stretches and contracts after microdeformations of the body at temperature extremes, provides insulation of the adhesive layer from moisture and dust, and protects it from crumbling. By making the lid chamfered around the perimeter of the upper outer side of the lid and ensuring that the end surface of the lid adheres to the chamfer surface on the inner surface of the vertical protrusion of the wall of the housing, the necessary space for laying the sealing composition is provided and leakage of the adhesive composition under the lid is avoided, which facilitates subsequent depressurization of the module and significantly increases its maintainability. The working gap between the chamfer surface and the inner surface of the vertical protrusion, filled with a sealing compound, provides easy access to the sealing joint if depressurization is necessary, while maintaining the reliability of sealing during module operation.

An additional technical result is to increase the adhesion of the sealant layer to the adhesive layer by applying a sublayer of the inventive composition to the surface of the adhesive layer before laying the sealant, which leads to an increase in the reliability and durability of the sealant. In addition, the film of the sublayer formed on the surface of the adhesive layer additionally provides moisture protection of the latter.

The use of the adhesive composition of the claimed composition allows to provide high physico-technical properties of the sealing joint. This technical result is achieved through the use in the adhesive composition of these substances in the claimed proportions. The inventive adhesive composition has passed lengthy tests, both laboratory and operational.

The resulting tight joint has high cohesion, adhesion to the walls of the metal body, gaplessness, resistance to temperature and pressure drops.

As the adhesive composition for implementing the method of manufacturing a sealed electronic module using a substance of the following composition, parts by weight:

modified epoxy resin 594-596 amine hardener 88-90 Bn 296-300 Cr ₂ O ₃ 16-20

As a modified epoxy resin, an K-139 grade epoxy-diane uncured modified resin is used, which is a composition based on an ED-20 grade epoxy resin, MGF-9 grade polyester and SKN-26-1A grade rubber or SKM 18-1A grade (TU 6 -05-211-1079-85). The use of a modified epoxy resin allows one to obtain a structure in which there are inclusions of elastic rubber in a rigid epoxy matrix, which contribute to the redistribution and dissipation of mechanical stresses arising from external influences. Such a structure is characterized by increased resistance to dynamic and erosive influences. The hardener UP-0633M makes it possible to stabilize the curing process. When it is used, the volatility and toxicity of epoxy compositions are significantly reduced, and the technological properties of the compositions vary widely due to an increase in the gelation time of the compositions, impregnation ability and adhesion, and also due to a decrease in viscosity. The hardener UP-0633M is highly resistant to mechanical stress and aggressive environments and is especially effective in coatings that are used where chemically and water-resistant surfaces are needed. This hardener is a low-viscosity liquid (10-100 MPa · s), which mixes well with the resin, plasticizing it. The use of this hardener makes it possible to avoid an avalanche-like curing reaction with rapid heating. The use of various fillers gives the adhesive composition various properties. The use of a mixture of boron nitride and chromium (III) oxide as a filler, due to their morphological features, increases dynamic strength, provides redistribution of mechanical stresses and counteracts the destruction of the adhesive layer under dynamic exposure. In addition, boron nitride provides the necessary thermal conductivity of the resulting adhesive. The adhesive composition of this composition has good adhesion to the walls of the metal body, the necessary thermal conductivity, mechanical strength, moisture resistance, dynamic stability, suitable for operation in the temperature range from -60 ° C to + 120 ° C and a maximum humidity of 98% at a temperature of + 35 ° C .

The adhesive composition is prepared as follows.

In a container of glass, polyethylene or other inert material add resin and filler in the indicated proportions and mix thoroughly with a spatula until a homogeneous mass is obtained. The container with the mixture is placed in a vacuum oven and evacuated at a pressure of 9.0-9.8 KPa for 30-60 minutes, depending on the amount of the mixture until the bubbles disappear. The cabinet is turned off and gradually increase the pressure to atmospheric. The container is removed, the necessary amount of hardener is poured into it and thoroughly mixed until a homogeneous mass. The container with the mixture is again placed in a vacuum oven and evacuated at a pressure of 9.0-9.8 kPa for 6-10 minutes. Thus obtained adhesive composition must be used immediately, no later than 20 minutes after preparation, during which it retains its fluidity.

The average test results of the proposed adhesive composition are presented in table 1.

Table 1. Property Indicator Density, g / cm ³ 1.29 Shear strength on a pair of D16-D16, MPa (kgf / cm ³ ) after exposure to elevated temperature of 120 ° C for 1000 h 11.9 (122) after exposure to elevated temperature of 200 ° C for 6 hours 9.4 (96) after exposure to relative humidity 98 ± 2%, 56 days. 9.4 (96) Shear strength on a pair of anodized alloy D16-D16, MPa (kgf / cm ³ ) 11.0 (113) Tensile shear strength on a pair alloy D16-D16 coated with tin-bismuth, MPa (kgf / cm ³ ) 11.7 (120) Mushroom resistance +

The inventive method is illustrated using Fig.1-2, which depict:

Figure 1 is a top view of the module;

Figure 2 is a cross section of a module.

In figure 1-2, the positions 1-19 are indicated:

1 - housing;

2 - cover;

3 - compartment;

4 - a partition;

5 - a vertical ledge;

6 - hole in the cover for a screw tie;

7 - a counter hole in the housing for a screw tie;

8 - technological hole for pumping air;

9 - microwave connector;

10 - RF connector;

11 - woofer connector;

12 - screw;

13 - working clearance;

14 - microstrip or textolite board;

15 - an internal cover;

16 - side wall;

17 - chamfer;

18 - adhesive layer;

19 - sealant.

A method of manufacturing a sealed electronic module is as follows.

The housing 1 and the cover 2 are made, for example, by turning aluminum alloys from the blanks. As an aluminum alloy, for example, D16 (GOST 4784-97) is used. The housing 1 is made integral with the side walls 16 around the perimeter and divided into compartments 3 by partitions 4. The side walls 16 are made with a vertical protrusion 5 along the outer perimeter of their upper surface. In the side walls 16, holes are made for microwave 9, treble 10 and bass 11 connectors.

The cover 2 is made with the dimensions of the upper and lower surfaces slightly smaller than the dimensions of the housing 1 along the inner contour of the vertical protrusion 5 of the side walls 16 so that when placing the cover 2 in the housing 1, the end surface of the cover 2 is in contact with the inner side of the vertical protrusion 5.

Along the perimeter of the cover 2, holes are made for a screw coupler 6 with a pitch of 15-50 mm, depending on the size of the housing 1. In the housing 1, holes corresponding to them are made 7. In the cover 2, a through technological hole 8 is made for pumping air.

Along the perimeter of the upper outer surface of the cover 2, a chamfer 17 is made.

An angle of 45 ° is preferred.

The dimensions of the housing 1 and cover 2 are selected in accordance with the formulas:

where h is the height of the end surface of the cover 2 to the level of the chamfer 17; H is the thickness of the cover 2; d is the thickness of the vertical protrusion 5; D is the thickness of the side wall 16, which is chosen equal to 4-8 mm

The indicated ratios make it possible to obtain an electronic module with the required level of shielding and strength while maintaining acceptable values of its mass.

The housing 1 and the lid 2 are first coated with a nickel layer 18-24 microns thick, then with a bismuth doped tin layer 15-21 microns thick. The use of nickel is due to its high intrinsic corrosion resistance. In addition, the nickel layer serves as a necessary sublayer for applying a tin-bismuth alloy layer. A protective coating based on a tin-bismuth alloy gives the surface of the housing 1 the ability to solder and resistance to external influences (moisture, salt fog) in accordance with the requirements of GOST 9.005-72 and RD 50-9.645.

In the prepared housing 1 place the assembly elements. First, solder the microwave 9, RF 10 and LF 11 connectors, placing them in the corresponding holes of the side walls 16. As microwave connectors 9 can be used standard AWG connectors or Rosenberger connectors. As the LF connectors 11 power and control can, for example, be used connectors Molex, ITW or Harwin. In the compartments 3 of the housing 1 are placed microstrip and textolite boards 14, fixing them to the housing 1 with screws 12 and connecting with the corresponding connectors. Compartments 3 are closed with internal covers 15 and fastened with screws 12 to the partitions 4.

After installing and adjusting the assembly, the housing 1 is covered with a cover 2, which is then screwed to the side walls 16 and to the partitions 4 with screws 12, if necessary. The sections of the end surface of the cover 2 to the surface of the chamfer 17 are adjacent to the inner surface of the vertical protrusion 5. A technological gap between the end surface of the cover 2 and the inner surface of the vertical protrusion 5 is allowed to be no more than 0.1 mm. The surface of the chamfer 17 and the inner surface of the vertical protrusion 5 form a working gap 13.

The surfaces forming the working gap 13 are degreased before applying the sealing compound. An adhesive composition based on epoxy resin is laid in the working gap 13 to the upper level of the side walls 16, which coincides with the upper plane of the cover 2. Due to the viscous structure and good adhesion to the metal, the adhesive composition fills all the cracks and compensates for surface irregularities. After application, the adhesive composition is cured. The module is placed in a control cabinet heated to a temperature of + 75 ± 5 ° C, and can withstand from 3.5 to 4 hours. Then the module is removed from the furnace and incubated for another 2 hours in air until the adhesive composition is completely cured. During the curing process, the adhesive composition shrinks, and in the cured state, the adhesive layer 18 occupies 2/3 of the height of the working gap 13. Since the adhesive composition has good adhesion to the metal, a hemispherical recess forms after curing. Thus, without the use of additional operations and special dosing, they provide an area for laying the sealant 19. For better adhesion of the sealant 19 to the surface of the adhesive layer 18, the latter is covered with a sub-layer - a mixture based on organic substances: polybutyl titanate, ethyl silicate-32 and white spirit. The ratio of the components of the sublayer is the following, wt.h:

polybutyl titanate 36-40 ethyl silicate-32 202-206 White Spirit 756-760.

This mixture is a low-viscosity clear liquid of light red color without sediment. Apply undercoat with a brush and incubated for 1.5-3 hours at room temperature in a fume hood. During this time, the white spirit evaporates and a thin film of polybutyl titanate and ethyl silicate-32 remains on the surface of the adhesive layer, a thin film of polybutyl titanate and ethyl silicate-32 remains on the adhesive layer, which increases the adhesion of the sealant 19 to the surface of the adhesive layer 18 and provides additional moisture protection of the latter. A sealant 19 is placed in the recess formed as a result of the curing of the adhesive composition. As a sealant 19, a silicone sealant of the VGO-1 brand (TU 38.303-04-04-90) is used, which is a white paste-like substance. The excess sealant 19 is removed with a scalpel to the level of the plane of the cover 2. After applying the sealant 19, the module is kept for 3 hours in air and 3.5 hours in an electrical cabinet at a temperature of + 75 ± 5 ° С. Air drying for 24 hours is also possible.

After sealing the working gap 13, air is pumped out of the module from the module 8 to a pressure of 13.33 Pa through the process hole 8 and the interior of the module is filled with inert gas, for example argon. After filling with inert gas, the process hole 8 is sealed.

In case of repair or replacement of elements of the electronic module, depressurization is carried out. For this, the sealant layer 19 is removed with a scalpel. Then the module is placed in a control cabinet, heated to 80 ° C, and incubated for 15-20 minutes. The softened adhesive layer 18 is removed with a scalpel.

As a result of using the proposed method for manufacturing a sealed electronic module, a sealed housing of the electronic module is obtained, which is suitable for protecting the onboard REA from the destabilizing effect of the environment. The operability of such a module is maintained for 15 years when stored under normal conditions and 5 years in adverse conditions, i.e. at high humidity and temperature.

Claims (2)

1. A method of manufacturing a sealed electronic module, including forming a housing with a vertical protrusion along the outer perimeter of the upper surface of the side walls of the housing, placing electronic components inside the housing, placing the lid in the housing, fixing it with screws to the housing, filling the working gap between the cover and the housing with an adhesive composition on based on epoxy resin and drying the module until the adhesive composition is completely cured, characterized in that the lid is formed with a chamfer around the perimeter of the outer upper side and times erami providing abutment end face cover to the chamfer surface to the inner surface of the vertical projection to form a working air gap between the chamfer surface and the inner surface of the vertical projection; after curing the adhesive composition, the surface of the cured adhesive composition is covered with a sublayer consisting of a mixture of polybutyl titanate, ethyl silicate-32 and white spirit, with the following ratio of components, parts by weight:
polybutyl titanate 36-40 ethyl silicate-32 202-206 White Spirit 756-760
and maintained until the white spirit is completely evaporated, then the working gap is filled with silicone sealant and dried until it is fully polymerized, while the adhesive composition based on epoxy resin contains a modified K-139 epoxy resin, UP-0633M amine hardener, boron nitride and chromium (III) oxide in the following ratio of components, parts by weight:
modified epoxy resin 594-596 amine hardener 88-90 Bn 296-300 Cr ₂ O ₃ 16-20 2. The method according to claim 1, characterized in that the housing and the cover are performed in accordance with the following ratios:

where h is the height of the end surface of the cover to the surface of the bevel; H is the thickness of the cover; d is the thickness of the vertical protrusion; D is the wall thickness of the body, which is chosen equal to 4-8 mm

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