JPH0227615A - Input and output cable for extremely low temperature integrated circuit - Google Patents

Abstract

PURPOSE:To prevent any trouble on contacts associated with heat contraction under an extremely low temperature by utilizing a vertically orientated polymer insulating layer as an insulating layer, and absorbing a heat strain due to a difference in a linear expansion among foreign materials of a signal wire, the insulating layer and a grounding conductor. CONSTITUTION:The first vertically orientated polymer insulating layer 5 comprising a signal wire (copper) 2, the first grounding conductor (copper) 3, the second grounding conductor (copper) 4 and poly-oxymethylene, and the second vertically orientated polymer insulating layer 6 comprising poly-oxymethylene are prepared. Then, an insulated conductor is formed by lamination by epoxy glue 7 so that the vertically orientated polymer insulating layers 5 and 6 may touch the signal wire 2. In the vertically orientated polymer insulating layers 5 and 6 a polymer crystalline granule block of which a molecule axis is orientated perpendicular to a surface of the grounding conductor intervenes between a surface that correlative signal wires are lined in parallel and the grounding conductor. Due to a spacing existing in a boundary of a crystalline granule within a surface paralleled to the grounding conductor, the heat strain may be absorbed. Accordingly any trouble on contacts associated with the heat contraction under the extremely low temperature may be prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an input/output cable for transmitting signals between an integrated circuit operating in a cryogenic environment and a device operating in a room temperature environment. The present invention relates to an input/output cable for cryogenic integrated circuits that does not cause contact failure due to thermal contraction of the circuit.

[Conventional technology]

Conventionally, this type of input/output cable has a cross-sectional structure as shown in Fig. 3 (U.S. Patent No. 4,44
1,088), in the turnout cable l, copper is used for the signal line 2, and polyester or polyimide, which has elasticity even at low temperatures, is used for the insulator 12 (PA, lJosko
witz et al., Cryogenics, 2
3.107 (1983), JP-A-6O-125002
). 13 is a copper ground conductor.

[Problem to be solved by the invention]

When a composite as described above is cooled from room temperature to an extremely low temperature, the temperature difference is as large as about 300°C, so thermal contraction cannot be ignored. Furthermore, since the linear expansion coefficients of the metal and polymeric materials are different, strain occurs at the interface. For example, if the cable length is 1.4n+ (P, ^, M.

Skowitz et al., Cryogenic
s, 23.107 (1983), ), copper has a coefficient of linear expansion of 1.4 x lO-' and shrinks by about 6 mIm. On the other hand, polyester has a coefficient of linear expansion of 7X10-'
29In+++ also contracts. Therefore, with an input/output cable that uses polyester as an insulator and has a cross-sectional structure as shown in Figure 3, the cable will bend and contract significantly like a bimetal under extremely low temperatures, so it will be difficult for integrated circuits placed under extremely low temperatures. It becomes difficult to maintain contact with the The coefficient of linear expansion of polyimide is 2.0x10-'
Although it is small among polymer materials and has a coefficient of linear expansion close to that of copper, even the popular cables made of such materials as insulators cannot be soldered due to heat shrinkage at extremely low temperatures. cause problems. For this reason, the contact structure is complicated, such as holding the contact with a spring (P, A, Mo5kov
Itz et al.

Cryogenics, 23.107 (1983)
,).

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an input/output cable for a cryogenic integrated circuit that does not cause contact failure due to thermal contraction at cryogenic temperatures.

[Means and actions to solve the problem]

The main feature of the present invention is that a vertically oriented polymer insulating layer is used as the insulating layer of the input/output cable for cryogenic integrated circuits, and thermal strain due to the difference in linear expansion coefficient between different materials can be reduced by vertically oriented This technology differs from conventional technology in that it allows absorption through a molecular insulating layer.

By uniaxially stretching a crystalline polymer such as polyethylene or polyoxymethylene, a polymer material in which molecular chains are oriented in the -axis direction can be easily obtained. It is well known that the coefficient of linear expansion in the stretching direction of such -axis-oriented polymers rapidly decreases with the stretching ratio and changes from zero to a negative value (A, C1ferri
and 1. M. Ward, Eds.

Ultra-High Modulus Polyme
rs, Appl, Sci, I, ondon
(1979); 1. M. Ward, Ed.”
Developments in Oriented P
o1yIlers-1″, Appl, Sci,,
London (19g2). For example, the coefficient of linear expansion (room temperature) of high-density polyethylene is 1.2xlO in the unstretched state.
-' to 1' to zero at a stretching ratio of 2 times, and at a stretching ratio of 18 times to -1,2xlO-' to 1'. For polyoxymethylene, the coefficient of linear expansion (room temperature) is 8.0XIO-
From '1 to 1', it is zero at a stretching ratio of 8x, and - at a stretching ratio of 20x.
4,0XIO-"l'"1.

However, the coefficient of linear expansion in the direction perpendicular to the stretching direction increases somewhat with increasing stretching ratio.

Therefore, as shown in FIG.
In between, it consists of an aggregate of polymer crystal blocks 16 whose molecular axes are oriented perpendicular to the conductor plane, and each crystal block 16 straddles between the opposing conductors 14 and 15, and parallel to the conductor plane. A void 17 is provided at the boundary of the crystal mass 16 in the plane,
In addition, the vertically oriented polymer insulated conductor has spacers (not shown) placed between the conductors in order to keep the distance between the conductors at a predetermined value during the manufacturing process, or an insulating layer without such spacers. In this case, the molecular axes of the polymers in the polymer crystal blocks 16 serving as the insulating layer are oriented perpendicularly to the conductor plane, and the crystal blocks 16 are connected to the conductors 14 facing each other.
．． 15, the coefficient of linear expansion of the insulating layer in the direction perpendicular to the conductor surface becomes small. In addition, since there are voids 17 at the boundaries of the crystal clusters 16 in a plane parallel to the conductor plane, the linear expansion coefficient of the insulating layer in the direction parallel to the conductor plane is large, even though the linear expansion coefficient of each crystal cluster 16 is large. Regardless, since the strain is absorbed by the void 17, the coefficient of linear expansion will be approximately equal to that of the conductor 14.15, or if the conductor 14.15 is bonded to a substrate such as silicon, the coefficient of linear expansion will be the same as that of the substrate. be equal.

As a method for orienting the crystalline polymer that forms the insulating layer perpendicularly to the opposing conductor plane, there is a method of applying an electric field as shown in Japanese Patent Application No. 62-305820 filed earlier by the present applicant. There is. In such an orientation method using an electric field, the crystalline polymer that becomes the insulating layer has a dipole moment in the direction of its molecular axis, or if it does not have a dipole moment, the monomer before polymerization has a dipole moment. This is essential.

Polyoxymethylene (POM), known as a general-purpose engineering plastic, has a molecular chain of 97 in the crystal.
It has a five-helical structure, and because the dipoles cancel each other out, it is not oriented by an electric field. However, formaldehyde, which is one of the monomers of POM, has a dipole moment of 2.27D (Debye) and is therefore oriented by an electric field. The present applicant has discovered that by polymerizing liquid formaldehyde under an electric field, an aggregate of POM crystal masses with molecular axes oriented perpendicular to the conductor plane can be obtained. this is,
This is because non-polar POM is also oriented in the direction of the monomer under the influence of the formaldehyde monomer oriented in the direction perpendicular to the conductor surface. As shown in Figure 4, scanning electron microscopy revealed that each POM crystal cluster straddles opposing conductors, and that there are voids at the boundaries of the crystal clusters in a plane parallel to the conductor plane. Do you get it. These voids are caused by unreacted monomers and low molecular weight P at the boundaries of crystal clusters.
The OM is collected and evaporated after polymerization.

This method of filling monomer in advance between opposing conductors and then polymerizing it to create a polymer insulating layer requires a spacer to maintain a predetermined distance between the conductors during the manufacturing process. Various materials can be used, such as glass fibers, granular inorganic materials, plastic films such as polyimide, and stretched oriented fibers and films.

In addition, in this method, if the conductor surface is made rough, the monomer can penetrate into fine pores, so even POM, which has poor adhesiveness, can be firmly bonded due to the so-called anchor effect. Furthermore, since the strength in the direction perpendicular to the conductor surface, that is, in the direction of the molecular axis, is extremely strong, the opposing conductors do not easily peel off or collapse, and have excellent shape stability. In addition, as in the case of the stretched and oriented sample, since it is oriented in one direction, it will not break even at extremely low temperatures.

In addition to the radiation method shown in Japanese Patent Application No. 62-305820, other polymerization methods include a method in which a polymerization catalyst is added to monomer in advance and then polymerized under an electric field, and a method in which a polymerization catalyst is applied to the surface of a conductor in advance and then polymerized. There are various methods, such as a method in which monomers are filled and polymerized under an electric field, and any of them may be used.

〔Example〕

FIGS. 1(a) to 1(c) show enlarged views of a part and cross-sectional structure of an input/output cable l for a cryogenic integrated circuit according to the present invention.

In Figures 1(a) to (C), 2 is a signal line (copper), 3
is the first ground conductor (copper), 4 is the second ground conductor (copper),
5 is a first vertically oriented polymer insulating layer made of polyoxymethylene, 6 is a second vertically oriented polymer insulating layer made of polyoxymethylene, and 7 is an epoxy adhesive.

Next, a method of manufacturing the above-mentioned lead-out cable for cryogenic integrated circuits will be explained. A spacer with a thickness of 125 μm between opposing commercially available electrolytic copper foils for printed circuit boards with a thickness of 35 μm.
μI glass fibers were placed at appropriate intervals (not shown)
. A vapor phase formaldehyde monomer produced by thermal decomposition of commercially available powdered paraformaldehyde was dehydrated and purified by passing it through a trap cooled to approximately -20°C with salt and ice through the gap between the opposing electrolytic copper foils. After, -78
Filled in liquid state at ℃. While applying a static voltage of 5 kV (electrolytic strength 0.4 MV/am) between opposing copper foils,
080 was carried out in the liquid phase at -78°C. The irradiation dose rate was 3×105R/h, and the irradiation time was 3 hours.

As a result, a vertically aligned polymer insulated conductor with a thickness of about 200 μm was obtained.

A microstrip line was constructed by patterning a plurality of signal lines 2 on the electrolytic copper foil on one side of this insulated conductor by etching. Further, on the signal line 2, a vertically oriented polymer insulating layer is placed on the insulated conductor with a thickness of approximately 160 μm, which is obtained by removing the electrolytic copper foil on one side of the vertically oriented polymer insulated conductor produced as described above by etching. I attached them with epoxy adhesive so that they were in contact with each other. As a result, an input/output cable for a cryogenic integrated circuit having a cross-sectional structure shown in FIG. 1 and a thickness of about 360 μm was obtained.

FIG. 2(a) shows an example of the connection between the input/output cable for a cryogenic integrated circuit according to the present invention and an integrated circuit placed under a cryogenic temperature.
, shown in (b). In the figure, the same symbols as in FIG. 1 indicate the same parts. 8 is a silicon substrate on which an IC chip is mounted, 9 is a solder bump, IO is a signal line (copper) on the silicon substrate, and 11 is a ground conductor (copper) on the silicon substrate. If such a connection part is placed in an extremely low temperature environment, if the insulating layers 5 and 6 are made of a polymer material with a high coefficient of linear expansion, such as polyester or polyimide, as in the past, due to the difference in coefficient of linear expansion with the copper or silicon substrate, Thermal distortion occurs and the solder bumps 9 come off, causing contact failure, but the vertically aligned polymer insulation 1
In 15 and 6, a polymer crystal mass whose molecular axis is oriented perpendicular to the ground conductor plane straddles between the ground conductor and the plane where the opposing signal lines are parallel, and is parallel to the ground conductor plane. Since there are voids at the in-plane boundaries of the crystal clusters, thermal strain can be absorbed. Therefore, even after repeated heat cycles between liquid nitrogen temperature and room temperature, the solder bumps did not come off and cause contact failure.

〔Effect of the invention〕

As explained above, according to the present invention, the vertically aligned polymer insulating layer absorbs the thermal strain caused by the difference in coefficient of linear expansion between different materials. It will not cause any damage at the contact points with integrated circuits placed at extremely low temperatures.

[Brief explanation of the drawing]

FIG. 1(a) is a perspective view showing a part of the input/output cable for a cryogenic integrated circuit according to the present invention, and FIG.
), Fig. 1(c) is an enlarged sectional view taken along line A-A' of
An enlarged sectional view along the line BB' in Figure (a), Figure 2 (a)
2(b) is a side sectional view showing an example of the connection between the input/output cable for a cryogenic integrated circuit according to the present invention and an integrated circuit placed under a cryogenic temperature, and FIG. FIG. 3 is a cross-sectional view of a conventional input/output cable, and FIG. 4 is a cross-sectional perspective view of a vertically oriented polymer insulated conductor. l... Input/output cable, 2... Signal line, 3... First ground conductor, 4... Second
ground conductor, 5... first vertically aligned polymer insulating layer, 6... second vertically aligned polymer insulating layer, 7...
... Adhesive, 8 ... Substrate (e.g. silicon), 9 ... Solder bump, 10 ... Signal line on the board, 11 ... Ground conductor on board, 1
2... Insulator (e.g. polyester or polyimide), 13... Ground conductor, 14.15...
...Conductor, 16... Vertically aligned polymer crystal mass, 1
7...Gap.

Claims (1)

[Claims] Between a plurality of parallel signal lines and a first ground conductor facing parallel to these lines, there is an aggregate of polymer crystal blocks whose molecular axes are oriented perpendicular to the ground conductor plane, and each of the crystal blocks is It straddles between the surface where the opposing signal lines are parallel and the ground conductor, and there is a gap at the boundary of the crystal mass in the plane parallel to the ground conductor surface, and the surface where the opposing signal lines are parallel The first type has spacers installed at various places between the ground conductor and the ground conductor to maintain a predetermined distance between the ground conductor and the surface where opposing signal lines are parallel, which are necessary during the manufacturing process. A cryogenic method characterized in that a second ground conductor is further provided on the signal line of the microstrip line provided with a vertically oriented polymer insulating layer via a second vertically oriented polymer insulating layer as described above. Input/output cable for integrated circuits.