GB2218932A

GB2218932A - Hot-press head for connection of electrodes

Info

Publication number: GB2218932A
Application number: GB8910827A
Authority: GB
Inventors: Toshiyuki Kawaguchi
Original assignee: Shin Etsu Polymer Co Ltd; Shin Etsu Chemical Co Ltd
Current assignee: Shin Etsu Polymer Co Ltd; Shin Etsu Chemical Co Ltd
Priority date: 1988-05-24
Filing date: 1989-05-11
Publication date: 1989-11-29
Anticipated expiration: 2009-05-11
Also published as: HK148995A; KR890017073A; KR950008482B1; JPH01170981U; JPH055675Y2; GB8910827D0; GB2218932B

Abstract

A hot-press head which comprises a metal hot plate 1 and a pad 3 respectively having at least one protrusion or concavity 2 and at least one concavity or protrusion 4, such that the plate and the rubber pad are mutually-engaging and freely demountable, and in which the pad 3 comprises a rubbery material having a hardness in the range from 50 to 80 according to the hardness scale specified in JIS (Japanese Industrial Standard) K 6301. The hot-press head is used for electrically connecting two electrodes or two arrays of electrodes or respective substrates facing each other with an interposed layer of an anisotropically electroconductive adhesive therebetween. The rubbery material of pad 3 may be silicone rubber compounded with 20 to 60% by volume of a highly heat-conductive powder such as a metal powder or inorganic oxide powder. <IMAGE>

Description

HOT-PRESS HEAD FOR CONNECTION OF ELECTRODES The present invention relates to a hot-pressing head for connecting electrodes or, more particularly, to a hot-pressing head used for electrically connecting two electrodes or two arrays of electrodes on respective substrates facing each other with an interposed layer of an anisotropically electroconductive adhesive therebetween.

It is very common in the assembling works of various kinds of electronic devices to use an electroconductive adhesive for electrically connecting two electrodes or two arrays of electrodes, for example, one, on a display unit such as a liquid-crystal display unit and, the other, on a circuit board bearing integrated circuits and other parts or on two circuit boards.Such a method is practiced in various different ways including a method in which an anisotropically electroconductive adhesive prepared by compounding an electrically insulating adhesive based on a thermoplastic or thermosetting thermoactive resin with 60% by volume or less of electroconductive fine particles (see Japanese Patent Kokai 61-20941) or an electroconductive adhesive prepared by compounding an electrically insulating thermoactive adhesive with elevtroconduc- tive fine particles such as carbon black and silver powder (see Japanese Patent Kokai 55-60987) provided at a pitch correspaond- ing to the pitch of the electrode arrangement in the arrays to be electrically connected is interposed between the electrode arrays and the substrates are pressed together with heating using a hotpressing head so as to exhibit the adhesive power of the adhesive mechanically bonding the electrodes together and simultaneously to establish electrical connection through the electroconductive particles dispersed in the interposed adhesive layer. Alternatively, it is also known that the electrodes in an array are formed from an electroconductive adhesive and the adhesive-formed electrodes are directly contacted with the electrodes of another array with heating under pressure so as to establish mechanical bonding and electrical connection therebetween.

In order to perform the above mentioned hot-pressing works under controlled conditions, a hot-pressing apparatus is used, of which a typical model is schematically illustrated in Figure 1 by a side view. In this apparatus, the hot-pressing head is composed of a hot-plate 13 made of, for example, a metal and provided with heater elements 12 built therein above a surface plate 11 and the hotplate 13 is pressed down by means of a pressing device 14. It is important that the hot plate 13 has a relatively large heat capacity and has built-in heater elements 12 in order to reduce the temperature decrease thereof when it is contacted with a work piece placed on the surface plate 11. Alternatively, the heater elements 12 may be heated up momentarily by passing a pulse-wise large electric current as in impulse sealers.

It is also known as is illustrated in Figure 2a that the surface of the hot-plate 13 of the hot-pressing head is covered with a hotpressing pad 15 made of a heat-resistant rubber such as a silicone rubber as being bonded with a layer of a heat-resistant adhesive 15a with an object to obtain a cushoning effect to compensate for the possible undulation or warping on the surface of the work piece as well as irregularities in the surface level due to the electrodes formed thereon. Alternatively, as is shown in Figure 2b, the hob pressing member 15 made of a heat-resistant rubber layer is adhesively bonded beforehand to a sheet or plate 15b of a metal having a high thermal conductivity such as aluminum and the laminate of the hot-pressing pad 15 and the metal plate 15b is adhesively bonded to the hot-plate 13 by means of the interposed layer 15a of an adhesive.Further alternatively, an aluminum plate 15b without the silicone rubber-made pad can be directly jointed to the hot plate 13 by fastening with screw bolts 16.

When the hot-pressing head as described above is used for electrical connection of electrode arrays by using an anisotropically electroconductive adhesive, following situations must be taken into consideration. Thus, anisotropically electroconductive adhesives generally have an active temperature of 100 to 150 0G at which the bonding power of the adhesive is exhibited. The length of time given to a single cycle of the bonding works is usually very short within 5 to 10 seconds. The silicone rubber-made pad 15 should have a thickness of at least 0.5 mm in order to fully exhibit a cushoning effect by absorbing the irregularity of the surface under pressing.Accordingly, it is very important that the efficiency of heat conduction from the hot plate 13 to the surface of the rubber pad 15 is as high as possible when the resistance against heat conduction is taken into consideration due to the thermal barrier of the adhesive layer 16a and/or the aluminum plate 15b. It is sometimes practiced in order to keep the surface of the rubber pad 15 at a sufficiently high temperature that the hot plate 13 is heated at a temperature of as high as 250 to 350 "C. This high temperature is of course detrimental against the durability of the rubber pad 15 even though the pad 15 is made from a heat-resistant rubber such as silicone rubbers so that the rubber pad 15 is subject to an increase in the hardness of the rubbery material before longterm running as a result of the thermal degradation of the rubber.

Once the hardness of the rubber pad 15 has been unduly increased, crack formation or chipping may be caused in the rubber pad which no longer is suitable for uniform hot pressing or not capable of conducting a sufficient quantity of heat to the anisotropically electroconductive adhesive so that uniformity of the adhesive bonding caanot be ensured to increase the contact resistance between the electrodes. These troubles must be dissolved by replacing the degraded rubber pad 15 with a new pad but such a replacing work is performed as being accompanied by a great decrease in the productivity of the production line due to the replacing works including removal of the adhesive layer 15a before the adhesive bonding work of a new rubber pad.

The present invention accordingly has an object to provide an improved hot-pressing head used for electrically connecting electrodes by melting a layer of an anisotropically electroconductive adhesive interposed therebetween without the above described problems and disadvantages in the conventional hot-pressing heads used for the same purpose.

Thus, the hot-pressing head of the invention comprises: (a) a hot plate having at least one concavity or protrusion; and (b) a pad member having at least one protrusion or concavity which is engaged with the concavity or protrusion, respectively, of the hot plate to hold the pad member attached to the hot plate without using an adhesive in a freely demountable way, the pad member being made from a rubbery material having a hardness in the range from 50 to 80 according to the hardness scale specified in JIS (Japanese Industrial Standard) K 6301.

Figure 1 is a schematic illustration of an apparatus used for hot-pressing. Figures 2a, 2b and 2c are each a cross sectional view of a conventional hot-pressing head.

Figures 3a and 3b are each a cross sectional view of a hotpressing head according to the invention as cut in a plane perpendicular to the longitudinal direction of the head. Figure 3c is a cross sectional view of a rubber pad having two protrusions.

Figures 4a to 4j are each a cross sectional view of a rubber pad according to the invention showing one of various modifications relative to the cross sectional configuration.

As is described above, the most characteristic feature of the inventive hot-pressing head is that the rubber-made pad attached to the hot plate is not in the form of a plane plate or sheet but has at least one protrusion and/or concavity which fit or are engaged with the concavity and/or protrusion, respectively, provided on the hot plate so as to hold the rubber pad attached to the hot plate even without using an adhesive or mechanical fastening means such as screw bolts in a freely demountable way. Thus, the rubber pad, when it is degraded to have an unduly high hardsness or damaged with cracks or chippings, can be easily and rapidly replaced with a new pad with minimum disturbance of the production line.In addition, the efficiency of heat conduction from the hot plate to the surface of the rubber pad can be improved owing to the increase in the contacting area between the hot plate and the rubber pad.

Figures 3a, 3b and 3c of the accompanying drawing are each a cross sectional view of a hot-pressing head according to the invention as cut in a plane perpendicular to the longitudinal direction of the head. The hot-pressing head illustrated in these figures is composed of a hot plate 1, which is made of a metal of good thermal conduction, and a rubber pad 3 attached to the lower surface of the hot plate 1. In the model illustrated in Figure 3a, the hot plate 1 is provided with a concavity 2 and the rubber pad 3 has a protrusion 4. When the rubber pad 3 is attached to the hot plate 1, the protrusion 4 of the rubber pad 3 is inserted into the concavity 2 of the hot plate to be in just fitting and gives a means of engagement to hold the rubber pad 3 attached to the hot plate 1 even without using any adhesive or mechanical fastening means such as screw bolts.Though not limitative, the concavity 2 and the protrusion 4 may be in the form of an elongated groove and in the form of an elongated rib, respectively, so as to improve the reliability of engagement. Though also not limitative, the interface 2a between the hot plate 1 and the rubber pad 3 is in parallel to the pressing surface 2b of the rubber pad 3. It is important at any rate that the hot plate 1 and the rubber pad 3 are contacted with each other over a surface area as wide as possible in order to ensure good heat conduction therebetween.

Figure 3b illustrates an alternative modification of the model shown in Figure 3a. In this case, the hot plate 1 is provided with a protrusion 6 instead of a concavity and the rubber pad 3 is provided with a concavity 7 so that the rubber pad 3 is attached to and held by the hot plate 1 with engagement between the protrusion 6 and the concavity 7.

Figure 3c is a cross sectional view of a similar rubber pad 3 which is provided with two protrusions 4 so as to increase the reliability of the engagement of the rubber pad 3 to a hot plate (not shown in this figure). When the rubber pad 3 has dimensions of the width of 5 mm and a height of 3 mm, for example, a preferable design of the rubber pad 3 is that the widths of A, B, C, D and E in the figure are each 1.0 mm and the heights of F and G are each 1.5 mm in order to obtain a good balance between reliability of the engagement between the hot plate and the rubber pad 3 and easiness in attaching and detaching the rubber pad 3 to and from the hot plate.

It is important that the pad member 3 is made from a rubber having a hardness in the range from 50 to 80 in the scale specified in JIS K 6301. When the hardness of the rubber pad 3 is too low, the rubber pad is greatly deformed when the hot-pressing head is pressed down on to a work piece so that the flow of the insulating adhesive covering the conductive particles in the anisotropically conductive adhesive would be insufficient so as not to give complete electrical connection between the electrodes. When the rubber forming the rubber pad 3 is too hard, on the other hand, the surface of the rubber pad can no longer follow and compensate the irregularities on the surface of the work piece under pressing so that the effect of adhesive bonding cannot be fully and uniformly exhibited.

It is also very desirable that the rubber forming the rubber pad is highly heat resistant and has a coefficient of thermal conductivity as large as possible. In this regard, a preferable rubbery material is a silicone rubber usually having a coefficient of ther- mal conductivity of 3.9 X 104 cal.cm-1.s-1.0C-1 or larger, which is a value as high as twice of the coefficient of most organic rubbers.

When it is desired to further increase the coefficient of thermal conductivity of a silicone rubber, it is optional that the silicone rubber is compounded with 20 to 60% by volume of a highly heatconductive powder as a thermal conductivity improver such as a powder of a metal, e.g., copper and aluminum, powder of an inorganic oxide or ceramic, e.g., titanium dioxide, spinel, aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, beryllium oxide, tin oxide, ceric oxide and the like. By this means, the coefficient of thermal conductivity of a silicone rubber can be increased to 2 to 20 X 10-3 cal.cm-l.s-l. C-l or even larger.

It is of course that the form of the protrusions and/or concavities provided in the hot plate and the rubber pad is not limited to the above described ones having an orthogonal cross section and the number of them is not limited to one or two. Figures 4a to 4j illustrate several possible modifications in the cross sectional configuration of the rubber pad. Needless to say, these figures are given only for the purpose of exemplification and not for the purpose of limiting the scope of the present invention.

It is an advantage that no difficulties or troubles are encountered in the work of attaching and detaching the rubber pad to and from the hot plate irrespective of the cross sectional configuration of the protrusions and/or concavities formed in the hot plate and the rubber pad. This advantage is due to the fact that the rubbery material forming the rubber pad has a larger coefficient of thermal expansion than metals forming the hot plate so that, even when the rubber pad is shaped to have such dimensions as not to cause any troubles with too much tightness in attaching and detaching at room temperature owing to deformation of the rubber, the engagement between the hot plate and the rubber pad is sufficiently tight and reliable due to the thermal expansion of the rubber pad in a somewhat larger extent than the metal-made hot plate at a high temperature of the working condition.

The rubber pad 3 should have a thickness as measured between the contacting surface with the hot plate 1 and the surface coming into contact with the work piece in working by disregarding the protrusion or concavity, i.e. the thickness expressed by G in Figure 3a, for example, in the range from 0.5 to 3 mm or, preferably, from 0.5 to 2 mm. The exact thickness should be adequately selected with consideration of the increased possibility of absorbing any undulation or warping in the surface of the work piece or irregularities of the surface due to the electrodes thereon formed, for example, of a copper foil by increasing the thickness and the decrease in the efficiency of heat conduction by increasing the thickness.

As is understood from the above given description, the hotpressing head of the invention is advantageous in respect of the reliability of mechanical and electrical connection between electrodes with stable adhesive bonding strength and contact resistance because the inventive hot-pressing head is constructed of a metal-made hot plate and a pad member made of a rubber having a specified hardness contacting with each other keeping a wide contacting area to ensure uniformity of the effect of hot pressing even without an overly increase of the temperature of the hot plate.

Moreover, the attaching and detaching works of the rubber pad to and from the hot plate can be performed very rapidly and conveniently at room temperature as compared with conventional hotpressing heads in which the pad member is attached to the hot plate by using an adhesive or by a mechanical means such as screw bolts while the engagement between the hot plate and the rubber pad is very firm and reliable due to the larger thermal expansion of the rubber pad than the metal-made hot plate at the high temperature of working also to ensure good heat conduction between the hot plate and the rubber pad.

Claims

1. A hot-press head which comprises a metal hot plate and a pad respectively having at least one protrusion or concavity and at least one concavity or protrusion, such that the plate and the rubber pad are mutually-engaging and freely demountable, and in which the pad comprises a rubbery material having a hardness in the range from 50 to 80 according to the hardness scale specified in JIS K 6301.

2. A hot-press head as claimed in claim 1, wherein at least one protrusion or concavity is in the form of an elongate rib or elongate groove, respectively.

3. A hot-press head as claimed in claim 1 or claim 2, wherein the pad comprises a silicone rubber.

4. A hot-press head as claimed in any preceding claim, wherein the pad is 0.5 to 3 mm thick.

5. A hot-press head as claimed in any preceding claim, wherein the rubbery material contains from 20 to 60% by volume of a thermal conductivity improver.

6. A hot-press head as claimed in claim 5, wherein the thermal conductivity improver is a powder of a metal or inorganic oxide.

7. A hot-press head according to claim 1, substantially as herein described with reference to any of the accompanying Figures 3a to 3c and 4a to 4j.