RU2481754C1 - Printed circuit board on metal substrate and method of its manufacturing - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: dielectric foiled at both sides is used (for instance, in the form of a flexible polymer) and a metal substrate with a plating layer, besides, a solder layer is arranged between them. In the metal substrate of the printed circuit board there might be through holes made for connection with other printed circuit boards. Besides, tinning of the printed circuit board is carried out simultaneously with tinning of the plating layer of the metal substrate, afterwards the printed circuit board billet is soldered to the metal substrate billet. It is possible to simultaneously solder radio elements to contact sites of the printed circuit board.

EFFECT: provision of the possibility to manufacture in conditions of a conventional assembly production facility both rigid and flexible-rigid printed circuit board on a metal substrate having increased strength, resistance to mechanical actions, improved heat removal and screening properties.

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Description

The group of inventions relates to electronic equipment, in particular, to the design of a printed circuit board on a metal substrate on a rigid or flexible-rigid basis, which is an integral part of multilayer printed circuit boards, as well as its manufacturing technology, and can be used at radio and electronic enterprises.

Boards on a metal substrate are widely used to solve the problems of heat dissipation in devices, where for some reason the installation of forced cooling elements is difficult or their power is insufficient for high-quality heat dissipation. The metal base in this case is used as a radiator. The effect of thermal stress of all components is reduced, which increases the durability of the elements and the product as a whole. Due to the fact that the board can be given any shape, it becomes possible to most optimally place it in the device and provide significant space savings, which is of exceptional importance with increased requirements for miniaturization of devices, for example, in aircraft.

In addition, due to the use of metal for the substrate, the printed circuit boards have good electromagnetic compatibility and shielding characteristics. The use of such boards increases the reliability of devices, MTBF, and resistance to mechanical stress.

Aluminum is usually used as the metal for the substrate, which allows not only to reduce the weight of the printed circuit board, but also significantly reduce its cost.

Printed circuit boards on a metal substrate are usually a structure consisting of three layers: a metallization layer, an insulating layer and a metal substrate (see, for example, ATV Electronics: manufacturing printed circuit boards on metal, http://www.businesskey.com/object / 84744 /).

The first layer is conductive. A topological drawing is applied to it, and then all that is superfluous is removed by etching, leaving only the necessary paths.

For the middle layer use an insulating material, certainly dielectric, with high strength. It is made from durable polymers, such as polyimide.

The third layer - the bottom layer of the board - an aluminum substrate with a thickness of 0.5 to 3 mm. The thickness of the metallized layer is chosen depending on the temperature regime and the calculated loads on the printed circuit board. To increase the corrosion resistance, aluminum substrates are usually anodized.

The disadvantages of the above boards include:

- the high complexity of manufacturing associated with the need for grinding and polishing aluminum substrates before anodizing;

- low adhesion of polymers to aluminum alloys;

- the difference in the coefficient of thermal expansion of the aluminum substrate and aluminum oxide obtained as a result of anodization, which causes cracking of the dielectric layer during thermal stresses (for example, soldering).

A technical solution is known, which is a board on a metal substrate, consisting of a conductive layer, a base of metal and a composite polymer layer located between them (Application US No. 20111111191, publ. 12.05.2011, B32B 5/00).

The disadvantages of the analogue.

The high complexity of manufacturing a composite polymer layer, the long technological cycle of manufacturing a printed circuit board on a metal substrate, and accordingly its high cost.

One of the options for the effective elimination of these shortcomings is the use of clad materials as bases.

Closest to the claimed solutions, the prototype is a technical solution according to PCT application No. WO 2010050896, publ. 05/06/2010, H01L 23/26.

The device is a printed circuit board on a metal substrate consisting of a base (material - aluminum, copper, gold, palladium, steel, zinc, tin, etc., aluminum is mainly used), plated, for example, with copper, which is characterized by good adhesion. A dielectric layer (material - polyimide, PET, other polymers) is deposited on a substrate using known methods, on which a conductive layer is applied (material - aluminum, copper, gold, palladium, steel, zinc, tin, etc., mainly copper is used), on which conductors of elements of a topological pattern are formed by etching in the form of paths, contact pads, etc.

The disadvantages of the prototype.

The deposition technology is quite laborious, characterized by high cost, low environmental safety, requires the organization of specialized production, which increases the final cost of the product. Therefore, the product cannot be manufactured, in particular, in the framework of traditional assembly production. Moreover, on the basis of the obtained product, it is possible to produce only rigid printed circuit boards, while there is a great demand for flexible-rigid structures on the market.

The technical result of the claimed technical solution (device) is to increase the strength of the product, its heat-removing and shielding properties, as well as the possibility of manufacturing flexible-rigid structures.

The technical result is achieved in that a board on a metal substrate containing a base with a plating layer, a dielectric located on the plating layer of the base, is characterized in that the dielectric is foil on both sides, and a solder layer is located between the plating layer of the base and the dielectric foil. The dielectric can be made of a flexible polymer, for example polyimide, and through holes can be made in the metal substrate.

Below the invention (device) is described in more detail with reference to the accompanying drawings, which depict:

Figure 1 - printed circuit board on a metal substrate.

Figure 2 - sectional view of a flexible-rigid board on a metal substrate.

A printed circuit board 1 on a metal substrate 2 with through holes 3 is proposed (FIG. 1). They serve for the manufacture of multilayer structures, connection to printed circuit boards on a rigid or flexible basis, or for volume connection with other devices (not shown).

Between the printed circuit board 1 and the metal substrate 2 there is a solder layer 4 (for example, a mixture of tin and lead), which strengthens the design of the printed circuit board. The metal substrate 2 comprises a base 5 (e.g., of aluminum) with a cladding layer 6 (e.g., of copper). The solder layer 4 together with the cladding layer 6 have a thickness of 0.4-0.7 mm, which is sufficient to effectively improve the shielding properties of the structure (D.N.Shapiro "Electromagnetic shielding", Scientific publication, Publishing house "Intellect", Dolgoprudny, 2010, pp. 28-33).

The printed circuit board 1 is a dielectric 7 foiled on both sides (for example, of fiberglass, flexible polymer, in particular polyimide, etc.) with the outer and inner layers 8 and 9 of the dielectric 7 foil (mainly copper is used for these purposes), which are formed by elements of a topological pattern, for example, contact pads 10, polygons 11, paths 12, false conductors 13 (Figure 2). Due to the small thickness and high electrical resistance of the dielectric, efficient heat removal from the radio element and electrical insulation of the conductors are provided.

At least one radio element 15 is located on the printed circuit board 1.

Through holes 3 can be placed under the radioelements 15 to provide the necessary thermal conditions.

The device operates as follows.

The heat from the heat-loaded radio element 15 passes through a copper layer 8, a polyimide layer 7, a copper layer 9, a solder layer 4, a cladding layer 6 and enters the base 5, which ensures the spread of heat throughout its volume and its efficient dissipation into the surrounding space. The linear expansion coefficients of the materials of the metal substrate 2, layers 8 and 9 of the dielectric foil 7, solder 4 are the same order of magnitude ("Guide to structural materials", MSTU Bauman, Moscow, 2005, pp. 239-259), which provides stability of the brazed joint under thermal stresses (for example, sudden changes in temperature, soldering, etc.). Moreover, the small thickness of the dielectric layer affects its stability slightly. Formed polygons 11 and false conductors 13 on the inner layer 9 of the dielectric foil 7 provide uniform spreading of the solder layer 4 when soldering and relieving stress at the junctions 14 from the rigid part to the flexible part of the printed circuit board 1. The soldered connection between the metal substrate 2 and printed circuit board 1, in contrast from bonding with adhesive (as in the prototype) it has increased strength and resistance to mechanical stress (for example, vibration, shock, etc.), which is essential when using printed circuit boards in electronic units mounted on aircraft.

The technical result of the proposed technical solution (method) is to reduce the complexity of manufacturing a printed circuit board, including flexible-rigid, if possible, its production in the conditions of the traditional assembly production of the instrument-making enterprise.

The technical result is achieved by the fact that in the method of manufacturing a board on a metal substrate, including the manufacture of a blank of a metal substrate with a base with a cladding layer, the manufacture of a blank of a printed circuit board from a dielectric foil on both sides, followed by a topological drawing on the dielectric foil, its etching and tinning, simultaneously with tinning of the printed circuit board, the cladding layer of the base of the metal substrate is tinned, after which the blank of the printed circuit board is soldered to the zag otovke metal substrate.

The method is as follows.

For the manufacture of a printed circuit board on a metal substrate, ready-made materials are used: a foil dielectric and a base with a plating layer.

Cut, for example on a milling machine, the workpiece of the metal substrate 2, in which, if necessary, through holes 3 are made.

A blank of the printed circuit board 1 is made of a dielectric 7 foiled on both sides, a topological drawing is applied to the foil, followed by etching of the outer conductive layer 8 in order to form tracks 12, contact pads 10, polygons 11, false conductors 13, etc. Next, simultaneous tinning of the cladding layer 6 of the metal substrate 2 and the outer conductive layer 8. Then, the blank of the printed circuit board 1 is soldered to the blank of the metal substrate 2 (by infrared, convection brazing, etc.). In the process of soldering, you can solder and the radio element (radio elements) 15 to the pads 10.

The manufacture of the product by this method using ready-made materials does not require sophisticated chemical equipment, additional control devices and the development of special technological processes, which significantly reduces the complexity of manufacturing, and allows it to be manufactured in the framework of traditional assembly production. The method allows, in addition to manufacturing rigid boards, to manufacture a flexible-rigid board on a metal substrate.

Due to the connection of the foil-coated dielectric with a metal substrate by the method of soldering with the simultaneous soldering of radio elements to the contact pads, wiring is significantly facilitated. In addition, it becomes possible to automate the manufacturing process, to increase the strength of the product and its resistance to mechanical stress. The presence of an additional metal layer in the form of solder increases the heat-removing and shielding properties of the printed circuit board. The use of a flexible polymer as a foil dielectric makes it possible to fabricate a flexible-rigid board on a metal substrate.

In this case, printed circuit boards on a metal base can be made in the conditions of the traditional assembly production of the instrument-making enterprise without the use of special equipment.

Thus, the proposed inventions make it possible to manufacture both rigid and flexible-rigid printed circuit boards on a metal substrate with less laboriousness, which have increased strength, resistance to mechanical stress, and improved heat-removing and shielding properties.

Claims (4)

1. A printed circuit board on a metal substrate containing a base with a plating layer, a dielectric located on the plating layer of the base, characterized in that the dielectric is foil on both sides, and a solder layer is located between the plating layer of the base and the dielectric foil. 2. A printed circuit board on a metal substrate according to claim 1, characterized in that the dielectric is made of a flexible polymer. 3. The printed circuit board on a metal substrate according to claim 2, characterized in that through holes are made in the metal substrate. 4. A method of manufacturing a printed circuit board on a metal substrate, including the manufacture of a blank of a metal substrate with a base with a cladding layer, the manufacture of a blank of a printed circuit board from a dielectric foil on both sides, followed by a topological drawing on the dielectric foil, its etching and tinning, characterized in that at the same time with tinning of the printed circuit board, the cladding layer of the base of the metal substrate is tinned, after which the workpiece of the printed circuit board is soldered to the workpiece of the substrate.

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