JPH0799378A - Method for forming resistor thin film layer on printed circuit board - Google Patents

Abstract

(57) [Abstract] [Purpose] A method for forming a resistor thin film layer of a printed circuit board which is uniform and highly reliable over a relatively wide range. [Structure] The conductor foil 4 is supported by a jig, stains on the foil are removed by a bomberment method, a resistor film 32 is formed on the soil-removed foil, and the resistor film 32 is laminated on a substrate 36, and then strain is removed. Therefore, thermocompression bonding is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer printed board, and more particularly to a method of forming a board having a thin resistor layer having high frequency characteristics.

[0002]

2. Description of the Related Art While digital computers and digital signal process circuits are required to have higher speeds due to their complexity, the demand for smaller peripheral independent circuits has led to the development of complex multilayer printed circuit boards. It was Many such substrates consist of layers of conductors that contain patterned components that act like special discrete components.

As a thin layer body useful for such a substrate, there is a thin layer resistor formed by photolithographically forming a predetermined resistor pattern, which is known in many other circuits on the substrate. Is connected by the method. There are many methods of making resistive thin film bodies by conventional plating methods. However, when used in relatively large, eg so-called "motherboards", these conventional resistance films tend to have a non-uniform thickness across the surface of the layer, which in turn leads to variations in resistance. Often, the accuracy of the signal characteristics is lacking, especially when the frequency is high.

The water pressure type thin layer method also has a problem of non-defective rate in the multilayer board using the same because of stress on the conductor.
Due to the difficulty of repairing such defective substrates and cost reduction, development of highly complete thin layer components, both electrically and mechanically, has been awaited.

The Applicant has much experience, especially with regard to nichrome independent resistor thin films, as an example of which, US Pat.
400,066; 3,622,410; 3,629,776; 3,691,007; 3,857,68
3; 3,930,975; 3,981,691; 4,021,277. In addition, the applicant is G. By Pawluk, “Elec
He is also familiar with "thin film resistors plated on substrates" published in etric Engineer Magazine.

One of the above-mentioned patents is to deposit a nichrome thin film on various structures by a conventional plating method, while the other patents do not stack thin layers that have already been formed on a multilayer substrate. The circuit of the required pattern is obtained by directly sputtering nichrome on the patterned portion.

The advantage of the latter thin layer forming method is that many resistors are incorporated in the substrate itself, so that the density of the resistors can be increased, and accordingly, the substrate surface has a margin.
Mounting C etc. and shortening the wiring distance. Further, since the inductance and the noise are reduced, the frequency characteristic and the speed of the substrate are improved, and the reliability is also increased because the independent wiring is limited to the minimum. By using different techniques for patterning, the number of resistors can be increased and replaced with part of the production line without further difficulty and expense.

[0008]

OBJECTS AND SUMMARY OF THE INVENTION Accordingly, a primary object of the present invention is to provide a thin layer resistor that is electrically and mechanically uniform throughout and that can be used in a multilayer printed circuit board.

Further, it is to produce a thin layer resistor including a resistor thin film mainly by spattering of nichrome.

It is an object of the present invention to provide a technique for uniformly supporting a conductor foil on a flat plate in a state of being electrically isolated from the ground potential.

Another object of the present invention is to provide a step of connecting the conductive foil and its supporting structure, charging the conductive foil in the opposite direction to the etchant, and removing dirt and a protective film on the foil by sputtering.

A technique for forming a thin layer by thermocompression bonding a conductor thin film covered with spatter under high pressure and high temperature to an epoxy resin as a support, and further, after thinning the layer, stress of the thin layer is released in a dry thermal environment. Technology and the like are included in the main purpose of the present invention.

The above-mentioned objects, advantages, and differences from the prior arts described above are presently the best for obtaining thin layers having better electrical and mechanical properties than the prior arts. It is noticeable in the possible production process.

In this process, first, there is a step of uniformly pressing a conductor foil selected on a flat plate to the periphery by using a jig and keeping a constant distance from a sputtering target so that a film thickness by sputtering becomes constant. Further, by ion bombardment method using argon gas or sputter etching method, the jig and the foil are charged opposite to the gas, and foreign matter and impurities are removed from the surface of the foil before the resistance film is deposited by PVD method such as sputtering. Provide a way to get rid of.

The resistance target material is preferably DC
Repeated sputtering using PVD method with magnetron sputtering. At this time, a nichrome-aluminum-silicon target is used.

In order to bond the conductor resistance foil to the support in a thin layer, the resistance is thermocompression-bonded to the resin support. A number of stacked layered structures are simultaneously bonded under a controlled environment of constant temperature and constant pressure. There is not much stress in the adhered thin layers, but it is possible to further reduce the stress by continuing baking and natural cooling.

The thin layer thus produced exhibits superior properties in terms of uniformity. Compared to a thin layer bonded by plating or a hydraulic machine, there is less variation in the resistance value over the entire surface of the thin layer, and the change in resistance value with time is also small. These features are all the more significant when incorporated into a multilayer printed circuit board that requires relatively high frequency signals.

[0018]

1 and 2 to 5 show a flow chart of a process for producing an improved thin layer 2 according to the present invention and a sectional view of a substrate through a main process. In this process, a selected copper foil whose electrical properties are known in advance is attached to the jig 6 (see FIGS. 6 and 7). Foil 4
Is brought into close contact with the entire flat flat plate 8. In this way, a uniformly flat coating surface is obtained.

The foil 4 is dressed as "hollow cathode effec".
Eliminating a harmful gap called “t” that occurs between the flat plate 8 and the foil 4 and increases the plasma density between the flat plate 8 and the foil 4.
The fact that the foil 4 has no distortion, twist, or wrinkle prevents distortion due to thermal expansion and maintains a constant distance between the target and the foil over the entire surface of the foil.

The jig 6 shown in FIG. 6 includes a flat plate 8 and metal frames 10 and 12 serving as two sturdy rectangular clasps.
It consists of a spring-like retainer / spacer 14 mounted around the metal frame. The metal frames 10 and 12 make it possible to deposit two foils 4 simultaneously. The front and rear clasps 16 are attached to the side of the flat plate 8, and when the metal frames are slidably pressed against the flat plate in cooperation with the metal frames 10 and 12, the metal frame is received on the foil 4 and the foil 4 is fixed. It is pulled and firmly fixed to the flat surface of the flat plate 8 with the central portions of the foils 4 on both sides exposed to the target.

A uniform pressure is obtained, in particular, by means of a number of spring retainers mounted on the support bars 18 inside the metal frames 10,12. When the metal frame is free, the spring retainer 14 projects obliquely from the frames 10, 12 at a constant angle, and when tightened under the clasp 16, the spring retainer 14 is parallel to the foil 4. There is. The clasp 16 includes a retainer 22 that slides left and right with respect to a pair of tightening screws 24, and a portion 20 that supports the retainer 22.

In FIG. 7, the jig 6 is subsequently placed in a DC magnetron sputtering chamber 26 having a sufficient size. The device consists of several chambers which are independent of each other, but allows the foil 4 to be moved between chambers as necessary to carry out the process steps described below.

In bombardment or sputter etching (see FIG. 3), the jig and the foil are biased together and the impact of the glow discharge of argon atoms causes contamination of the surface of foil 4 and formation of a protective film. Remove layers. The contaminants adhere to the walls of the chamber. The exposure time, intensity, and gas conditions in the room are given in the conventional manner. Another possible technique is the sputter etch method, which either chemically pretreats or uses a highly reactive gas, depending on the material used.

As can be seen further from FIG. 7, the jig mold is supported by a carrier 28 and rails with rollers. The carrier 28 is designed such that the mold 6 is electrically independent of the grounding of the wash chamber. That is, during the above-described sputter etching, the external power source is connected so that the gas charged positively can be charged negatively as much as necessary. Specifically, the connection plate 54 on which the jig mold 6 is seated or the spatter shield is connected to the power source by the conductor 50 and the connector 52. Furthermore, the insulator 56,
58 and 60 isolate the jig die 6 from other cleaning chamber portions.

As shown in FIG. 4, the conductor foil 4 thus cleaned is transferred to the sputtering chamber. Here, the target and foil are appropriately biased and exposed to atoms freed from the selected target mounted on the inner walls of the chamber in close proximity. This is done in an environment under a glow discharge of argon. Atoms emitted from the target land on the foil 4 and form a thin film 32. A single sputter cycle usually produces a uniform and constant thickness film. A film 32 having a desired thickness can be obtained by performing many sputtering cycles.
Get In this example, the thickness is 500 to 800 angstroms.

Any mutations on the surface must be avoided as they will become larger or increase in number in later processes. As another film deposition method, vacuum deposition or CVD can be considered. Other sputtering methods include DC diode, RF diode, RF magnetron and the like.

56% nickel, 38% chrome, 4
% Aluminum, 2% silicon target provides a resistive film 32 having electrical properties suitable for its intended use. Various other targets or targets of different composition can give similar results.
Other potential resistor target materials include:
There are nickel-vanadium, tantalum nitride, phosphorus-nickel, chrome-aluminum, and the like.

Nichrome having a nickel content of 50% to 80%, a chrome content of 20% to 40%, and other components of 0% to 10% has poor stability, and is commonly used for the same purpose. It is thought that it gives a more electrically preferable film in terms of width compared to nickel and other plated materials.

Depending on the size of the printed circuit board desired,
The size of the sputtering chamber 26 for depositing the film is selected.
51cm x 129x5c which is currently used.
There is a sputter chamber large enough to form two thin m layers. Larger and smaller chambers can be used as well.

Once the desired conductor and resistor film 32 have been formed, this film 32 must then be adhered to a suitable glass epoxy resin substrate 36. The finished structure 2 is further processed into the multilayer printed circuit board shown in FIG. Another example of an insulating substrate that can be used is modified e.
poxies, tetra-functional epoxies, high temperature epoxies, bi
smaleimide blends, polyimides, modified polyimide
s, cyanate esters, etc.

In the above adhesion and in FIG. 5, the formed resistor film 32 is the glass epoxy resin insulating substrate 36.
In addition, instead of the conventional hydraulic bonding, thermocompression bonding is performed by high temperature and uniform pressure throughout. For hydraulic bonding, apply the thin layer 2 to the multilayer substrate 3
Used only when crimping to 8.

During the thermocompression bonding process, the stress is not so much applied to the resistor film 32. If a hydraulic press is used, the directional distortion generated in the insulating substrate 36 can be avoided by heating the film 32 and uniformly applying pressure to the entire surfaces of the insulating substrate 36 and the film 32.

In the process of thin-layer thermocompression bonding shown in FIG. 5, a number of resistor films 32 are used as insulating substrates 36 as their counterparts.
It is crimped at the same time. That is, each film 32 and insulating substrate 36 pair has a layered "book" -like structure separated by layers of inactive material (not shown). This "book" is placed in a bag (not shown) and numbered. Then, several "books" are stacked vertically and set in an autoclave.

Bonding is performed by applying pressure, temperature and time which are conventionally defined. In the meantime, the adhesive surfaces of the resistor film 32 and the insulating substrate 36 go through an adhesive process by heat so as to sufficiently support each other, and a permanent bond is formed to construct a multilayer substrate. In this example, a bond strength of 7 to 10 pounds per inch is obtained. Strengths of 3 to 7 pounds with other materials.

The thin layer thus formed has a relatively small amount of stress in it, but is further heat-treated under normal atmospheric pressure. As a result, the stress generated in the above-mentioned pressure bonding process is removed, and the epoxy insulating substrate 36 becomes more comfortable with the foil 4.
This process is carried out in an autoclave or another oven as a second heat treatment process under normal atmospheric pressure,
After that, it is naturally cooled to room temperature.

The thin layer 4 thus produced is taken out from the bag, washed, unnecessary portions in the periphery thereof are cut off, and appropriate marking is made according to each unique property.
In preparation for the subsequent processing, for example, the processing of the structure shown in FIG. 8,
A protective film or an oxide film may be formed on the conductor foil 4.

Finally, referring to FIG. 8, the subsequent steps are the formation of the ground plane (ground plana) and the conductive path (conductive p).
aths) formation, more complex multi-layer formation, and the like. In the thin layer body 38, the conductor foil 4 is photolithographically processed to form a large number of electrodes 40. These electrodes 4
0 is formed on an individual resistor or resistor region 42 of a predetermined size determined by the area of the resistor film 32 between the electrodes 40. Another conductor foil 4 is bonded to the lower surface of the insulator 36 as a ground plane. External circuitry (not shown) with electrodes for connecting wires, holes for loading other components (not shown), and other connections required And subsequently formed to connect the laminar structure 38 with Instead of the ground conductor foil 4, it is possible to add a thin layer body containing a new resistor to the structure 38.

As described above, by using the sputtered and thermocompression-bonded thin layer 2, the multilayer structure 38 which is practically much more mechanically and electrically uniform than the one formed by the conventional plating method or the like. Can be formed. This structure 3
8 is particularly advantageous for high frequency digital circuit design.

[Brief description of drawings]

FIG. 1 is a flow chart showing the steps in the process of making this thin layer.

FIG. 2 is a cross-sectional view of a thin layer made by the manufacturing process of FIG.

3 to 5 are cross-sectional views showing that a substrate is formed into a layered structure by the method according to the present invention.

FIG. 6 is a sketch drawing showing the assembly of a jig die for preparing a conductor foil prior to sputter deposition.

FIG. 7 shows a conductor foil jig attached to a roller type carrier in a film deposition chamber.

FIG. 8 is a partial cross-sectional view of a multilayer structure using this thin layer.

[Explanation of symbols]

 4 Conductor foil 8 Flat plate 32 Resistor film 36 Insulator 40 Electrode 42 Resistor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H05K 3/46 E 6921-4E

Claims (1)

[Claims] 1. A step of (a) securely adhering a conductor metal foil to a flat surface of a support; (b) a step of exposing the foil to a necessary time during glow discharge to remove dirt on the foil surface. (C) exposing the foil during glow discharge to form a resistor film on the foil from a resistor target; (d) placing the resistor film on a substrate under an inert gas. And a step of thermocompression-bonding the whole body with a uniform pressure, the method comprising: forming a resistor thin film layer on a printed circuit board.