RU2386225C2 - Method of making printed circuit boards with built-in resistors - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: when making printed circuit boards, the insulating layer used is aluminium nitride. Built-in resistors are put into openings with deposition of an insulating layer of aluminium nitride on walls of the openings, and a current conducting layer is also deposited on the butt ends of the built-in resistors. The conductive pattern of the circuit is made through deposition of a photomask, galvanic reinforcement of the thickness of the conducting layer, deposition of a protective metal resist, removal of the photomask and etching the conducting layer from gaps, or the current conducting layer is galvanically reinforced first, a photomask is put into contact pads, conductors and location of the butt ends o the built-in resistors, the current conducting layer is etched from the gaps, the photomask is removed, a protective solder mask is put and the contact pads and walls of the mounting openings are serviced. The printed circuit boards with built-in resistors are checked for conformity with GOST 23752-79 Printed circuit boards. General specifications and stability of retaining resistance values for a long period of time under 10 times overloading conditions is checked.

EFFECT: increased thermal scattering power of resistors built into printed circuit boards, improved removal of heat from elements mounted on the printed circuit board.

3 cl, 1 dwg

Description

The invention relates to the technology of manufacturing printed circuit boards and can be used in the electrical, radio, electronics and instrumentation in the manufacture of double-sided printed circuit boards.

A known method of manufacturing a printed circuit board with a heat sink, in which an insulation layer from the Al-ON system and a conductive layer is deposited on a printed circuit board base made of an aluminum plate, vacuum mask is applied, a photomask is applied, the thickness of the conductive layer is galvanically increased, and the photomask is removed by differential etching form a conductive pattern [1].

The disadvantages of the described method are: the lack of information about the possibility of obtaining printed circuit boards with metallized holes and the possibility of obtaining built-in resistors.

There is also a known method of manufacturing printed circuit boards with built-in resistors, in which holes are formed in printed circuit boards made of FR4-ML material, which are filled with resistive paste, and the resistive paste forms contact with the electrical layers of the printed circuit board [2].

The disadvantage of this method is the poor thermal conductivity of FR4-ML and overheating of resistors in a closed volume.

Thus, on the basis of two sources [1, 2], one can talk about the possibility of manufacturing printed circuit boards with built-in resistors based on the use of a metal plate as the base of the printed circuit board, followed by coating the surface of the board and hole walls with an insulating layer, applying a conductive layer to the surface of the board and wall mounting holes and the formation of a conductive pattern drawing.

The basis of the invention is the creation of a method of manufacturing printed circuit boards with built-in resistors, which would increase the heat dissipation power of the resistors built into the printed circuit boards, as well as improve heat dissipation from elements mounted on the printed circuit board.

The problem is solved in that aluminum nitride is used as an insulating layer, built-in resistors are placed in holes with an applied aluminum nitride insulating layer on the walls of the holes, and the conductive layer is also deposited on the ends of the built-in resistors.

Formation of the conductive pattern of the circuit is carried out by applying a photomask, galvanically enhancing the thickness of the conductive layer, depositing a protective metal resist, removing the photomask and etching the conductive layer from the gap places, or first galvanically conductive layer is reinforced, the photomask is applied to the contact pads, conductors and the locations of the ends of the built-in resistors, the conductive layer is etched from whitespace, the photomask is removed, a protective solder mask is applied and the contact pads and Enki mounting holes.

The drawing shows a diagram of the manufacture of double-sided printed circuit boards according to the proposed method, which has two options for forming a conductive pattern. Thin lines depict what coincides with the prototype or analogue, and thick lines represent different operations and sections.

The manufacturing process of double-sided printed circuit boards according to the proposed method includes the following operations: obtaining a workpiece 1, drilling mounting holes and holes for built-in resistors 2, applying a layer of aluminum nitride 3, filling holes with resistive paste to form built-in resistors 4, drawing on the surface of the states, the ends of the built-in resistors and the walls of the mounting holes of the conductive layer 5, the application of a protective pattern 6, galvanic build-up of the conductive layer 7, the application of a protective metal etching 8, removing the protective pattern and the conductive layer from the gap points 9, galvanically building up the conductive layer 10, applying the protective pattern to the conductive layer 11, etching the conductive layer from the blank spaces and removing the protective pattern 12, applying a protective mask for soldering 13, tinning the contact sites 14.

. Это позволяет эффективно отводить тепло от резистора в металлическое основание 15.An example of the manufacturing process of double-sided printed circuit boards with integrated resistors is implemented in the following sequence. From sheets of metal with high thermal conductivity, for example, M0 grade copper, in step 1, workpieces 15 of the required size are cut. In the blanks, in accordance with the board drawing, in step 2, mounting holes 16 and holes for built-in resistors 17 are drilled. Then, in step 3, a layer of aluminum nitride 18 with a thickness of 3 ... 5 μm is deposited on the surface of the workpiece with drilled holes by high-frequency reactive magnetron sputtering in a vacuum installation spraying URMZ. 297.014. The aluminum nitride layer has high dielectric properties: resistivity R _S = 10 ¹⁴ Ohm · cm [3] and high thermal conductivity

. This allows you to effectively remove heat from the resistor to the metal base 15.

In operation 4, the hole 17, the walls of which are covered with a layer of aluminum nitride, is filled with resistive paste 19. A resistor is formed, the resistance of which, according to [2], is calculated by the formula

where H is the thickness of the metal base, mm;

D is the diameter of the hole, mm;

ρ is the resistivity of the resistive paste, Ohm · mm;

π = 3.14 is a constant.

By selecting the thickness of the metal base N, the hole diameter D and the resistivity of the resistive paste ρ, the value of the obtained resistance can be varied over a wide range.

. В то же время у нитрида алюминия

, а у металлического основания из меди

. Поэтому резисторы, размещенные в отверстиях основания из металла, могут рассеивать большую мощность, обеспечивая высокую теплонапряженность печатной платы.When forming a resistor in the holes of the base made of FR-4 fiberglass, as stated in [2], the heat transfer from the resistor to the base material will be poor, since the heat transfer coefficient is

. At the same time, aluminum nitride

, and at the metal base of copper

. Therefore, resistors located in the holes of the base of the metal can dissipate a lot of power, providing high thermal stress of the printed circuit board.

To ensure electrical contact with the elements of the printed circuit board image on the surface of the printed circuit board, the walls of the mounting holes 16 and the ends of the resistor 19, in step 5, a copper film 20 is deposited on a vacuum deposition machine URMZ.297.014 by means of reactive RF magnetron sputtering. The film thickness is 5 ... 8 microns. It is enhanced by galvanic buildup of the conductive layer 21 to a thickness of 25 ... 30 microns. Using a photoresist, a protective pattern 22 is formed, which protects the copper layer during copper etching from whitespace, or which leaves open areas for galvanic copper deposition and build-up of the etching protective metal resist 23.

The protective figure 22 is removed and the conductive layer 20 is etched from places that are not protected by the metal resist layer 23, or first the conductive layers 20 and 21 are etched away from the gaps that are not protected by the protective figure 22. Then a protective mask is applied for soldering 24. The contact areas are covered Finish 25, providing good solderability of the PCB.

Testing of the method was carried out using basic (standard) technological equipment for the manufacture of double-sided printed circuit boards, two vacuum deposition units URMZ.297.014, which implements the method of reactive RF magnetron sputtering, for operations 3 and 5 and for setting the dosed supply of resistive paste for operation 4.

For the experiment, a board with a metal base of copper 2.0 mm thick with mounting holes with a diameter of 0.8 mm and holes for resistors with a diameter of 0.4 mm was chosen. The accuracy class of printed circuit boards corresponded to 3-4 class. The size of the printed circuit boards did not exceed 130 × 130 mm and was limited by the size of the location of the target.

After loading the board into the deposition unit URMZ.297.014, aluminum nitride was deposited on the entire surface of the board and the hole wall with a thickness of 3 ... 5 μm. Thickness was measured during the spraying process using the frequency method.

The holes were filled with resistive paste on the TRASSA-4304 installation. The required range of resistor values was provided by the required hole diameter and the resistivity of the resistive paste. So with a hole diameter of 0.4 mm and a resistivity of the resistive paste of 25 Ohm · mm, the resistance value of the resistor will be

The conductive copper layer 20 was applied on a vacuum deposition unit URMZ.297.014. Layer thickness 5 ... 8 microns. The control was carried out in the process of spraying by the frequency method.

Next, the boards were processed throughout the cycle.

Fabricated printed circuit boards with built-in resistors are tested for compliance with the requirements of GOST 23752-79 “Printed circuit boards. General technical conditions ”and are controlled for the stability of the preservation of resistance values during continuous operation under the condition of 10-fold overload. The tests of the manufactured printed circuit boards confirmed their high quality while maintaining the required structural and technological characteristics.

Using the invention gives the following effect compared to the prototype: increasing the dissipation power of the resistor on the board according to the proposed technical solution by 10 times compared with the option of placing the resistor in the hole of the board made of FR-4, with similar parameters.

Information sources

1. A method of manufacturing a printed circuit board with a heat sink. Verfahren zum Herstellen einer wärmeableitenden Leiterplatte: Application 19641397 A1 Germany, IPC ⁶ H05k 1/05 / Reiter Martino, Wolkers Lutz, Brikholtz Peter; Siemens AG. - No. 196413974; declared 9/9/96; publ. 2.4.98.

2. The embedded resistance in the holes of the printed circuit boards. Innenlegende Widerstände in Borungen von Leiterplate: Application 10015269 A1 Germany, IPC ⁷ H05k 1/16 / Crasser Eduard, Katzir Helmut; Siemens AG - No. 10015269; declared 28.3.2000; publ. 06.26.2001 (prototype).

3. Dobrynin A. V., Kazakov N. P., Naida G. A., Roddenezhny E. N. et al. Aluminum nitride in electronic technology // Foreign Electronics. M., Issue 4, 1989, pp. 44-84.

4. Properties of elements, Part 2. Chemical properties. Reference / Antonova N.N., Brakhnova I.T., Borisova A.L. et al. Ed. G.V.Sameonova. M. Metallurgy, 1976.338 s.

5. Lysov V., Kochergin V. Printed circuit boards with a metal base // Printed mounting, No. 3, 2007, p.23.

6. Kuhling X. Handbook of Physics. Translation from it. under the editorship of E.M. Leikina. M., Mir, 1985, table 28.

Claims (3)

1. A method of manufacturing printed circuit boards with built-in resistors, based on the use of a metal plate as the base of the printed circuit board and subsequent coating of the surface of the board and hole walls with an insulating layer, filling the holes with resistive paste, applying a conductive layer to the surface of the board and wall of the mounting holes and forming a conductive pattern circuits, characterized in that aluminum nitride is used as the insulating layer, built-in resistors are placed in the holes with the insulated an aluminum nitride layer on the walls of the holes, and a conductive layer is also applied to the ends of the built-in resistors. 2. The method according to claim 1, characterized in that the formation of the conductive pattern of the circuit is carried out by applying a photomask, selective galvanic amplification of the thickness of the conductive layer, selective deposition of a protective metal resist, removal of the photomask and etching of the conductive layer from whitespace. 3. The method according to claim 1, characterized in that the formation of the conductive pattern of the circuit is carried out by galvanically enhancing the thickness of the entire conductive layer, applying a photomask to the contact pads, conductors and the location of the ends of the built-in resistors, etching the conductive layer from whitespace, removing the photomask, applying protective solder mask and tinning of contact pads and walls of mounting holes.

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