Method of mounting a plurality of electronic parts on a circuit board

A method of mounting electronic parts on a circuit board comprises an adhesive layer formation step of forming, on an electrode surface of each electronic part on which electrodes are formed, a film-like thermosetting adhesive layer having an area substantially equal to that of the corresponding electrode surface so as to obtain adhesive-coated electronic parts. The electrodes on which the adhesive layer is formed are arranged so as to face corresponding electrodes of the circuit board, and the electrodes are positioned relative to each other. Heat and pressure are applied to the electrodes of the electronic parts and the electrodes of the circuit board to fix the electrodes to each other after the electrodes are positioned. Almost no adhesive superfluously comes out of the electrode surfaces. Accordingly, when mounting the electronic parts on the circuit board, it is unnecessary to remove superfluous adhesive, unlike conventional process, whereby the efficiency is improved and also the cost can be cut down.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of mounting a plurality of 
electronic parts on a circuit board, and also to a method of producing 
adhesive-coated electronic parts suited for use in the mounting method. 
2. Description of the Related Art 
With a recent trend to smaller-sized, thinner electronic parts such as 
semiconductor chips ("electronic parts" referred to herein include 
resistors, capacitors, semiconductor chips, etc. mounted on circuit 
boards), circuits and electrodes used in such electronic parts have 
increased density and finer connection pitch. Since fine electrodes are 
difficult to connect by soldering, recently, connection methods using 
adhesive are widely used. The connection methods include a method in which 
electrically conducting particles are mixed in an adhesive, and contact 
bonding is performed to achieve electrical connection in the thickness 
direction of the adhesive (e.g., Unexamined Japanese Patent Publication 
(KOKAI) No. 55-104007). There is another method in which no conducting 
particles are contained in an adhesive, and contact bonding is performed 
to achieve electrical connection through direct contact of fine 
irregularities on the electrode surfaces (e.g., Unexamined Japanese Patent 
Publication (KOKAI) No. 60-262430). 
The connection methods using adhesive permit connection at relatively low 
temperatures and also provide excellent reliability because the 
interconnecting portion has flexibility. In addition, in the case where 
adhesive formed into a film or tape is used, it is possible to supply the 
adhesive of uniform thickness in the form of a long strip, whereby the 
mounting line can be automated. Also, a simple step of applying heat and 
pressure simultaneously attains electrical connection between electrodes 
of the semiconductor chip and the circuit board and mechanical connection 
of the two through bonding. This is why the connection methods using 
adhesive are attracting attention. 
In recent years, multi-chip modules (MCM) which employ a, more elaborate 
form of the above methods and in which a large number of chips are mounted 
at high density on circuit boards of relatively small size are drawing 
attention. In general, an MCM is fabricated by forming an adhesive layer 
on a circuit board, peeling a separator, if any, from the adhesive layer, 
and positioning chips such that their electrodes face corresponding 
electrodes on the circuit board, followed by bonding of the electrodes. 
Forming an adhesive layer on a chip instead presents the problem that a 
complicated apparatus is required because a chip having a smaller area 
than the circuit board needs to be applied with an adhesive layer. 
Electronic parts used in MCM include a variety of chips such as 
semiconductor chips, active elements, passive elements, resistors and 
capacitors. 
Thus, various types of chips having different sizes (areas, heights) are 
mounted on MCM. When connecting chips to a circuit board, however, a 
problem arises which is not associated with conventional techniques such 
as the method of forming an adhesive layer on a circuit board or the 
heat-pressure bonding method. 
Specifically, in the case where the adhesive used is in the form of a film, 
adhesive strips (adhesive tapes) with different widths are needed 
depending on different chip sizes. In MCM, however, multiple chips are 
mounted at high density on a small-sized circuit board, and thus only a 
small mounting space is available, making it difficult to use a variety of 
tape widths. Also, use of various tape widths increases the labor involved 
in the management of materials. Further, since different devices for 
feeding, contact bonding, tape rewinding, etc. are needed for individual 
tape widths, the mounting apparatus is inevitably increased in overall 
size and is complicated, requiring a large installation space and 
increasing the cost. 
An attempt has therefore been made to mount various sizes of chips after an 
adhesive layer is formed on the entire surface of a circuit board 
(Examined Japanese Patent Publication (KOKOKU) No. 61-27902). With this 
method, however, much labor is required to remove the remaining adhesive 
from non-connecting sections, and also the cost increases because the 
adhesive layer is formed uselessly on regions other than the mounting 
sections. Further, since the adhesive is applied to the entire surface of 
the circuit board, heat applied at the time of connection can adversely 
affect adjacent chip mounting sections. For example, the reaction of the 
thermosetting adhesive may progress to such an extent that the adhesive on 
an adjacent section where a chip is not yet mounted becomes unusable, or 
an adjacent chip may develop a connection defect as the adhesive softens 
due to the connection heat even after the chip is mounted. This is also 
the case with removal of a defective chip after chip mounting. Namely, it 
is difficult to peel off a defective chip and also to remove the adhesive 
because of the reaction of the thermosetting adhesive. 
Also, as an attempt to form an adhesive layer with a size substantially 
equal to the chip size, Examined Japanese Patent Publication (KOKOKU) No. 
4-30742, for example, discloses forming an adhesive layer on a wafer and 
then subjecting the wafer to full dicing. In this case also, various types 
of adhesive-coated wafers must be prepared for different types of chips, 
making the process control complicated in view of the shelf stability life 
of the adhesive. 
Unexamined Japanese Patent Publications (KOKAI) No. 63-276237 and No. 
2-199847, for example, disclose applying an adhesive only to the top faces 
of bump electrodes (also merely called bumps) on a chip, in order to 
reduce the connectable pitch. However, since the adhesive is applied only 
to the top faces of the bump electrodes, the bump electrodes are bonded to 
a circuit board only in areas around the bump electrodes, so that the 
bonding strength and the connection reliability are low. In order to also 
apply the adhesive to regions other than the top faces of the bump 
electrodes, an underfill material needs to be poured, which, however, 
complicates the process and increases the cost. 
Further, in the case where chips with different heights are mounted or 
chips are mounted on both surfaces of a circuit board, heat and pressure 
cannot be uniformly applied by using conventional techniques generally 
employed, such as a press method in which a chip-carrying board is clamped 
by parallel mold elements or a pressure roll method using parallel rolls. 
Thus, it is impossible to connect fine electrodes in this situation. 
SUMMARY OF THE INVENTION 
The present invention was created to eliminate the above-described 
drawbacks, and an object thereof is to provide a method of efficiently 
mounting electronic parts on a circuit board, groups of adhesive-coated 
electronic parts suited for use in the mounting method, and a method of 
producing adhesive-coated electronic parts. 
According to a first aspect of the present invention, there is provided a 
method of mounting a plurality of electronic parts on a circuit board by 
bonding and fixing electrodes of the electronic parts to the circuit board 
to electrically connect the individual electronic parts to the circuit 
board. The method comprises: an adhesive layer formation step of forming, 
on an electrode surface of each of the electronic parts on which the 
electrodes are formed, a film-like thermosetting adhesive layer having an 
area substantially equal to that of the corresponding electrode surface, 
to obtain adhesive-coated electronic parts; a positioning step of 
arranging the electrodes (on which the adhesive layer is formed) so as to 
face corresponding electrodes of the circuit board and positioning the 
electrodes relative to each other; and a heat-pressure bonding step of 
applying heat and pressure to the electrodes of the electronic parts and 
the electrodes of the circuit board to fix the electrodes to each other 
after the electrodes are positioned. 
According to the first aspect of the invention, the adhesive layer is 
formed beforehand on the electrode surface of each electronic part. The 
electrode surface thus applied with the adhesive is affixed to 
corresponding electrodes on the circuit board, so that almost no adhesive 
superfluously comes out of the electrode surfaces. Accordingly, when 
mounting the electronic parts on the circuit board, it is unnecessary to 
remove superfluous adhesive, unlike the conventional process, whereby the 
efficiency is improved and the cost can be reduced. 
The electrodes are bonded to the circuit board with heat and pressure 
applied thereto after the electrodes are set in position, and therefore, 
the electrodes can be shifted as needed and thus can be positioned with 
accuracy. Even in the case where electronic parts with different heights 
or sizes are mounted, the electrodes of the electronic parts are 
individually fixed with heat and pressure applied thereto, whereby the 
electrodes can be applied uniformly with heat and pressure and the 
electronic parts can be easily mounted with reliability. In particular, it 
is possible to connect fine electrodes. 
Preferably, the area of the film-like adhesive layer falls within a range 
of .+-.30% with respect to the area of the electrode surface of the 
corresponding electronic part. If the area of the adhesive layer is 
greater than the .+-.30% range, too much adhesive comes out of the 
electrode surfaces, possibly requiring the adhesive removing step; on the 
other hand, if the area of the adhesive layer is smaller than the .+-.30% 
range, then there is the possibility of the electronic parts failing to be 
satisfactorily connected. 
The electronic parts are preferably held by a heating head by means of 
suction, for example, so that the surfaces of the electronic parts can be 
heated by the heating head. The heating head serves to locate the 
electronic parts in a predetermined position while holding the same, and 
then to immediately heat the electronic parts to be bonded and fixed to 
the circuit board. Thus, the apparatus and the process can be simplified. 
The heat-pressure bonding step preferably includes an inspection step of 
inspecting the electrical connection between the electrodes while the 
cohesive strength of the adhesive is increased to such an extent that the 
connection of the electrodes can be maintained. Namely, while the 
electronic parts are temporarily fixed with the cohesive force of the 
adhesive increased, the electrical connection is inspected. Even in the 
case where defective connection is discovered, repair work can be easily 
carried out because the electronic parts are fixed only temporarily. 
According to a second aspect of the present invention, there is provided a 
method of mounting a plurality of electronic parts on a circuit board by 
bonding and fixing electrodes of the electronic parts to the circuit board 
to electrically connect the individual electronic parts to the circuit 
board. The method comprises: an adhesive layer formation step of forming, 
on an electrode surface of each of the electronic parts on which the 
electrodes are formed, a film-like thermosetting adhesive layer having an 
area substantially equal to that of the corresponding electrode surface, 
to obtain adhesive-coated electronic parts; a temporary fixing step of 
positioning the electrodes of the electronic parts (on which the adhesive 
layer is formed) so as to face corresponding electrodes of the circuit 
board, and increasing cohesive strength of the adhesive to such an extent 
that connection of the electrodes can be maintained; and a heat-pressure 
bonding step of applying heat and pressure to the temporarily fixed 
electrodes to fix the electrodes to each other, the heat-pressure bonding 
step including simultaneously heating a plurality of electronic parts in 
an autoclave with a static pressure applied thereto within the autoclave. 
According to the second aspect of the invention, in the heat-pressure 
bonding step according to the first aspect of the invention, a plurality 
of electronic parts are simultaneously heated in the autoclave under the 
static pressure within the autoclave. Thus, multiple electronic parts can 
be easily bonded and fixed at one time with a simple arrangement. 
Also in the second aspect of the invention, the area of the film-like 
adhesive layer preferably falls within a range of .+-.30% with respect to 
the area of the electrode surface of the corresponding electronic part, as 
mentioned above. 
Further, the heat-pressure bonding step preferably includes an inspection 
step of inspecting the electrical connection between the electrodes while 
the cohesive strength of the adhesive is increased to such an extent that 
the connection of the electrodes can be maintained. Namely, while the 
electronic parts are temporarily fixed with the cohesive strength of the 
adhesive increased, the electrical connection is inspected. Even in the 
case where a defective connection is discovered, repair work can be easily 
carried out because the electronic parts are fixed only temporarily. 
According to a third aspect of the present invention, there is provided a 
group of adhesive-coated electronic parts each having an electrode surface 
coated with a film-like adhesive layer. The adhesive-coated electronic 
part group comprises: a connection sheet including a film-like adhesive 
layer and a separator from which the film-like adhesive layer can be 
peeled; and a plurality of electronic parts arranged on the film-like 
adhesive layer of the connection sheet, each of the electronic parts being 
affixed to the adhesive layer at an electrode surface thereof. 
According to the third aspect of the invention, a plurality of electronic 
parts are affixed to the adhesive film. Therefore, when the electronic 
parts are used, the separator film is pulled off, so that the electrode 
surface of each electronic part is coated with the adhesive layer. Namely, 
adhesive-coated electronic parts can be readily obtained, and in the case 
where electronic parts are mounted on circuit boards, a connection sheet 
with electronic parts affixed thereon is prepared and the electronic parts 
are peeled off of the connection sheet, thereby obtaining adhesive-coated 
electronic parts ready for use. Consequently, the control of the mounting 
process is facilitated, and also the adhesive-coated electronic parts have 
excellent shelf stability. 
Preferably, the adhesive layer contains electrically conducting particles. 
The conducting particles serve to electrically connect electrodes facing 
each other with reliability and also to insulate adjacent electrodes from 
each other. 
According to a fourth aspect of the present invention, there is provided a 
method of producing an adhesive-coated electronic part having an electrode 
surface coated with a film-like adhesive layer. The method comprises: a 
connection sheet placement step of arranging a connection sheet including 
a film-like adhesive layer and a separator from which the adhesive layer 
can be peeled, the connection sheet having a size greater than that of an 
electrode surface of an electronic part on which electrodes are formed; a 
contacting step of bringing the electrode surface of the electronic part 
into contact with the adhesive layer; a heating step of heating the 
electrode surface to form a cohesion reduction line at which cohesive 
strength of the adhesive lowers, at a location between a region of the 
adhesive layer corresponding to the electrode surface and a region of the 
adhesive layer surrounding the electrode surface; and a separating step of 
separating the electronic part from the connection sheet such that part of 
the adhesive layer having a size substantially identical with that of the 
electrode surface is separated from the separator and adheres to the 
electrode surface. 
According to the fourth aspect of the invention, the electrode surface of 
the electronic part is brought into contact with the connection sheet, and 
the electrodes are heated so that the cohesive strength of the adhesive 
around the electrodes may lower. Namely, the adhesive sets with a certain 
cohesive strength at normal temperature, but the cohesive strength lowers 
(or the adhesive softens) when the adhesive is heated up to a 
predetermined temperature. Accordingly, when the electronic part is 
separated from the connection sheet, part of the adhesive layer 
corresponding in size to the periphery of the electrode surface separates 
from the separator and adheres to the electrode surface, thus easily 
obtaining an adhesive-coated electronic part which is coated with an 
adhesive layer having a size substantially equal to that of the electrode 
surface. 
The cohesion reduction line is formed along the periphery of the electrode 
surface and is the boundary between a region of the adhesive layer where 
the cohesive strength lowers when the electrodes are heated and a region 
of the adhesive layer where the cohesive strength remains almost the same. 
In the case of adhesive, cohesive property is different from setting or 
hardening property (activation). Thus the former term is applicable to 
both thermosetting adhesive and heat softening adhesive. 
According to a fifth aspect of the invention, there is provided a method of 
producing an adhesive-coated electronic part having an electrode surface 
coated with a film-like adhesive layer. The method comprises: a connection 
sheet placement step of arranging a connection sheet including a film-like 
adhesive layer and a separator from which the adhesive layer can be 
peeled, the connection sheet having a size greater than that of an 
electronic part; a contacting step of bringing an electrode surface of the 
electronic part on which electrodes are formed into contact with the 
adhesive layer; a cutting step of pressing the electrode surface against 
the adhesive layer and cutting at least part of the adhesive layer along a 
periphery of the electronic part; and a separating step of separating the 
electronic part from the connection sheet such that part of the adhesive 
layer is separated from the separator and adheres to the electrodes. 
According to the fifth aspect of the invention, the electrode surface of 
the electronic part is pressed against the adhesive layer of the 
connection sheet, and the adhesive layer is cut along the electrode 
surface (electronic part) to thereby separate part of the adhesive layer 
which is in contact with the electrode surface from the other part of the 
adhesive layer. Consequently, it is possible to easily obtain with 
reliability an adhesive layer having a size substantially identical to 
that of the electrode surface of the electronic part. 
Preferably, the cutting step is achieved using a cutter arranged at a 
pressure head for pressing the electrodes of the electronic part against 
the connection sheet, or using a heating wire. Using the cutter arranged 
at the pressure head or the heating wire makes it possible to easily 
obtain an adhesive layer having a size substantially equal to that of the 
electronic part or the electrode surface. 
Preferably, the connection sheet is placed on a surface plate with a 
cushioning member interposed therebetween. In this case, the impact at the 
time of application of pressure by the pressure head or at the time of 
cutting can be absorbed. 
Further, the adhesive layer preferably contains electrically conducting 
particles in order to enhance the insulating property of an electrode from 
adjacent electrodes, as mentioned above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be hereinafter described with reference to the 
drawings illustrating embodiments thereof. 
FIG. 1 schematically illustrates, in section, an embodiment of the present 
invention. FIG. 1A shows part of a heat-pressure bonding apparatus used in 
a mounting method according to the present invention. An adhesive tape 6 
consisting of an adhesive layer 4 and a separator 5 is arranged between a 
heating head 2, which is capable of fixing a chip 1 thereon by, for 
example, suction and a surface plate 3. The adhesive layer 4 is positioned 
so as to face an electrode surface of the chip (semiconductor chip) 1 as 
an electronic part. The electronic part used in this case may be an 
element other than the semiconductor chip, such as an active element, a 
passive element, a resistor or a capacitor. 
The adhesive tape 6 is brought into close contact with the surface plate 3 
by, for example, suction. Alternatively, it may be allowed to travel while 
being kept taut by rolls or the like (not shown) arranged in front and at 
the rear of the surface plate 3, respectively. The adhesive layer 4 can be 
peeled from the separator 5. Since the separator 5 is in close contact 
with or kept taut on the surface plate 3, the separation of the adhesive 
layer 4 from the separator 5 is facilitated. 
Pressure is developed between the heating head 2 and the surface plate 3, 
whereupon the electrode surface of the semiconductor chip 1, on which 
electrodes are formed, is brought into contact with the adhesive layer 4 
having a greater area than the electrode surface. The adhesive layer 4 
preferably has a size corresponding to the largest size of multiple chips 
to be mounted on an MCM so that the adhesive layer 4 can be used for other 
chips as well and can be handled with ease. In this case, the size of the 
adhesive layer 4 is selected so as to correspond to the shorter side of 
the chip with the largest size, whereby the width of the adhesive tape can 
be narrowed and the installation space for the apparatus can 
advantageously be reduced. 
The width of the adhesive layer 4 (more generally, the width of the 
adhesive tape) may be substantially equal to the shorter side of the chip 
as shown in FIG. 2A, or may be slightly greater than the shorter side of 
the chip as shown in FIG. 2B. Alternatively, the adhesive layer 4 may have 
such a size that two chips can be arranged in the width direction of the 
adhesive layer 4, as shown in FIG. 2C. Any of these tape widths may be 
selected taking account of handling and mass-productivity. 
Referring again to FIG. 1A, the heating head 2 is heated up to a 
predetermined temperature to directly heat a back surface of the chip 1 
which is opposite the electrode surface, so that a region of the adhesive 
layer corresponding to the chip size is preferentially heated. During the 
heating, a region of the adhesive surrounding the chip 1 is scarcely 
heated and maintains the form of a film because the adhesive has low heat 
conductivity and thus little heat is transmitted to the surrounding 
region. On the other hand, a region of the adhesive layer 4 which is in 
close contact with the chip 1 adheres fast to the chip 1 as the viscosity 
lowers, or tackiness increases, due to the application of heat, thus 
increasing the film strength. Consequently, a cohesion reduction line 
across which the cohesive strength of the adhesive layer 4 lowers is 
formed along the periphery of the chip 1. 
The heating temperature of the head 2 is set to a temperature at which the 
adhesive layer 4 softens and melts (its viscosity is preferably 1000 
poises or less, more preferably 100 to 10 poises) and at the same time the 
hardening reaction of the adhesive is not initiated or at a low level (the 
rate of reaction is 20% or less) , and is selected appropriately depending 
on the type of adhesive used. Further, the head 2 is preferably heated at 
a temperature lower than or equal to the activation temperature of a 
latent hardener, mentioned later, in order to improve the shelf stability 
of adhesive-coated chips. 
FIG. 1B shows a state in which the heating head 2 is moved away from the 
surface plate 3, and as illustrated, part of the adhesive layer 4 
substantially equal in size to the chip 1 can be separated along the 
cohesion reduction line of the adhesive layer corresponding to the 
periphery of the chip 1 and adhere to the chip 1. Although the adhesive 
layer 4 on the surface plate 3 has an adhesive-free region from which 
adhesive has been transferred to the chip 1, the adhesive tape 6 maintains 
the form of a film because of the presence of the separator 5 and the 
remaining adhesive 4. Adhesive can be set on the surface plate 3 by 
removing the adhesive-free region or by moving the adhesive tape 6. 
In the case shown in FIGS. 1A and 1B, an adhesive-coated chip to which the 
adhesive layer 4 has been transferred from the separator 5 is obtained. 
Thus the adhesive-coated chip can be directly connected to a circuit 
board, permitting continuous fabrication of the MCM. When keeping the 
adhesive tape in stock, a separator may be affixed to the adhesive layer. 
In the arrangement of FIGS. 1A and 1B, various chips may be placed 
beforehand on the tape so that adhesive-coated chips can be efficiently 
obtained by removing the chips from the tape. In this case, a variety of 
adhesive-coated chips can be continuously fed in desired order, thus 
improving the productivity. 
FIG. 3 is a schematic sectional view showing the manner of obtaining an 
adhesive-coated chip according to another embodiment of the present 
invention. FIG. 3 shows part of a pressure bonding apparatus, and an 
adhesive tape 6 consisting of an adhesive layer 4 and a separator 5 is 
placed between a pressure head 8, to which a chip 1 is fixed by suction, 
for example, and a surface plate 3. The adhesive tape 6 is brought into 
close contact with the surface plate 3 by suction, for example. 
Alternatively, the adhesive tape 6 may be allowed to travel while being 
kept taut by rolls or the like (not shown) arranged in front and at the 
rear of the surface plate 3, respectively. 
The pressure head 8 is provided with a cutting jig 7. The cutting jig 7 has 
an edge extending along the periphery of the chip 1; in the case where the 
size of the chip in the width direction of the adhesive tape is 
substantially equal to the tape width, the cutting jig 7 may have two 
straight edges extending across the tape width. The adhesive layer 4 is 
cut by the cutting jig 7 in the thickness direction for at least a part or 
the whole of the depth thereof, thereby allowing part of the adhesive 
layer 4 with a size substantially equal to the chip size to adhere to the 
chip 1. At this time, the pressure head 8 may not be heated, in which case 
the fabrication work can be performed at room temperatures, making it 
possible to prevent the adhesive from being adversely affected by heat. A 
razor made of metal, ceramic, etc., or energy rays such as heat, 
ultraviolet radiation, laser beam, etc. can be used as the cutting jig 7. 
In the case where a cutting tool is used as the cutting jig 7 and the 
adhesive layer is cut by pressing the cutting jig 7 downward, the height 
of the cutting jig 7, (that is, the distance from the connection surface 
of the chip 1) is determined taking account of the depth to which the 
adhesive layer 4, or both the adhesive layer 4 and the separator 5, are to 
be cut. The adhesive layer 4 is preferably cut for its whole depth in view 
of ease of separation of the adhesive-coated chip from the tape. The 
cutting jig 7 may in this case comprise a vertically movable mechanism 
which can be contained in the pressure head 8 so that continuous 
production efficiency can be enhanced. 
In the arrangement shown in FIGS. 1A and 1B or in FIG. 3, a cushioning 
layer 11 made of rubber or the like may be interposed between the surface 
plate 3 and the separator 5, as shown in FIG. 4. In this case, a chip 
coated with adhesive corresponding in size to the periphery of the chip 
can advantageously be obtained with ease. 
Various examples of adhesive-coated chips obtained in the above-described 
manner will be now explained with reference to FIGS. 5A to 5D and FIGS. 6A 
to 6C. In all examples described below, the electrode surface of the chip 
1 is covered on its entirety with an adhesive film having an area 
substantially corresponding to the chip size. 
FIG. 5A illustrates a basic structure of the adhesive coated chip, in which 
the semiconductor chip 1 and the adhesive layer 4 are of a substantially 
identical size. FIGS. 5B and 5C illustrate cases where the size of the 
adhesive layer 4 is made somewhat different from that of the semiconductor 
chip 1 for adjustment of the optimum amount of adhesive after the 
connection to a circuit board. The size of the adhesive layer preferably 
falls within a range of about .+-.30% with respect to the chip size in 
view of the shape stability of the adhesive-coated chip, and more 
preferably, the adhesive layer should be identical in size with the 
semiconductor chip. In the present invention, the sizes of the adhesive 
layers shown in FIGS. 5A to 5C are regarded as substantially identical 
with the size of the semiconductor chip. FIG. 5D illustrates the case 
where the separator 5 remains affixed to the adhesive layer 4, in which 
case dust or the like can advantageously be prevented from adhering to the 
adhesive layer while the semiconductor chip is kept in stock. 
FIGS. 6A and 6B illustrate the cases where the chip has bump electrodes 12, 
and FIG. 6C illustrates the case where the chip has a wiring layer 13 
instead of bump electrodes. In FIGS. 6A and 6B, the adhesive contains 
electrically conducting particles 14, and in FIG. 6C, the adhesive 
contains no conducting particles. The structures shown in any FIGS. 6A to 
6C can be combined in desired manner with respect to the bump electrodes 
and the presence/absence of conducting particles. 
FIG. 7A illustrates a group of adhesive-coated chips, wherein a plurality 
of chips are placed separately on the separator with their entire 
electrode surfaces covered with adhesive films of substantially identical 
size. The tape with the chips affixed thereon can be rolled up. 
As shown in FIG. 7B, adhesive films 4a, 4b and 4c corresponding in size to 
respective chips may be present only on regions of the separator 5 where 
the chips are separately affixed. In this case, by arranging various chips 
on the separator in order of mounting on a circuit board, for example, it 
is possible to continuously feed adhesive-coated chips in order, thus 
enhancing the productivity. 
The adhesive-coated chips obtained in the above-described manner may be 
used for single-chip mounting, and also for multi-chip mounting as 
described below. 
First, using a microscope or an image storage device, the electrodes of 
each adhesive-coated chip are positioned accurately with respect to 
corresponding electrodes on a circuit board. For the positioning, 
registration marks may also be used. Subsequently, the electrodes to be 
connected to each other are applied with heat and pressure, so that 
multiple chips are electrically connected to a single circuit board. In 
this case, heat and pressure may be applied to one chip at a time, but if 
multiple chips can be bonded at the same time, the productivity is greatly 
enhanced. 
To apply heat and pressure, besides an ordinary press method, a static 
pressure method using an autoclave etc. may be used whereby chips with 
different thicknesses or sizes can be applied uniformly with heat and 
pressure. The static pressure mentioned herein denotes a constant pressure 
acting perpendicularly on the surface of an object. In general, the chip 
is 2 to 20 mm square, whereas the interconnecting section is 1 mm or less, 
in many cases 0.1 mm or less, in thickness and thus is by far smaller than 
the chip area, permitting a sufficient pressure to act in the direction of 
connection of the electrodes. 
During the application of heat and pressure, continuity test may be 
conducted to examine the electrical connection between electrodes to be 
connected to each other. Since continuity test can be performed while the 
adhesive is not set at all or is insufficiently set, repair work is 
facilitated. Preferably, the test is conducted when the rate of reaction 
of the adhesive is about 30% or less, in order to facilitate repair work 
using solvent. Where the rate of reaction of the adhesive is lower than 
10%, pressure is preferably applied since the fixing of the electrodes is 
not firm enough. 
In this manner, a plurality of chips 1 with different shapes or sizes are 
mounted on a circuit board 9 via the adhesive layer 4, as shown in FIG. 8, 
thereby obtaining a multi-chip module (MCM) in which chips are mounted at 
high density on the circuit board 9 of relatively small size. The circuit 
board 9 to which the present invention can be applied includes, for 
example, a plastic film of polyimide, polyester, etc., a composite 
material such as a glass fiber-epoxy composite material, a semiconductor 
of silicon etc., and an inorganic substrate of glass, ceramic, etc. 
For the adhesive layer 4 used in the present invention, thermoplastic 
materials and various other materials which set upon receiving heat or 
light can be used. Preferably, those materials which set upon receiving 
heat or light are used since they exhibit excellent heat resistance and 
humidity resistance after the connection. Among these, an epoxy adhesive 
containing a latent hardener and an acrylic adhesive containing a radical 
hardener such as peroxide are especially preferred because they set in a 
short period of time, can improve the efficiency of the connection work, 
and have excellent adhesive properties due to their molecular structure. 
The latent hardener has a relatively distinct activation point at which 
heat- or pressure-induced reaction starts, and thus is suited for the 
present invention involving the heat/pressure application step. 
As the latent hardener, imidazole, hydrazide, boron trifluoride-amine 
complex, amine-imide, polyamine salt, onium salt, dicyandiamide, and 
modified substances thereof may be used singly or in combination to form a 
mixture. 
These are catalytic hardeners of ionic polymerization type such as anionic 
or cationic polymerization type, and are preferred because they can set 
rapidly and because no special attention needs to be paid to chemical 
equivalents. Among the catalytic hardeners, an imidazole hardener is 
especially preferred since it is non-metallic and thus is less susceptible 
to electrolytic corrosion. The imidazole hardener is also used in view of 
reactivity and connection reliability. Further, other hardeners such as a 
polyamine hardener, a polymercaptan hardener, a polyphenol hardener and an 
acid anhydride hardener can be used, and also these hardeners may be used 
in combination with the aforementioned catalytic hardeners. A 
micro-encapsulated hardener in which the hardener as a core material is 
covered with a polymeric substance or an inorganic substance is also 
preferred because of its opposing properties, that is, long-term shelf 
stability and rapid setting property. 
The hardener for the adhesive used in the present invention should 
preferably have an activation temperature of 40 to 200.degree. C. If the 
activation temperature is lower than 40.degree. C., the difference between 
the activation temperature and room temperature is so small that the 
adhesive needs to be kept at low temperature. If the activation 
temperature is higher than 200.degree. C., other chips and the like are 
adversely affected by heat during the connection. For this reason, the 
activation temperature should preferably fall within a range of 50 to 
150.degree. C. The activation temperature mentioned herein represents an 
exothermic peak temperature of a compound of epoxy resin and the hardener, 
as a sample, which is measured by using a DSC (differential scanning 
calorimeter) while the sample is heated from room temperature at a rate of 
10.degree. C./min. With low activation temperature, good reactivity is 
achieved but the shelf stability tends to lower, and therefore, suitable 
activation temperature is selected taking this into consideration. 
According to the present invention, the shelf stability of adhesive-coated 
chips is improved by carrying out heat treatment at a temperature lower 
than or equal to the activation temperature of the hardener, and excellent 
multichip connection is achieved at a temperature higher than or equal to 
the activation temperature. Preferably, therefore, the melt viscosity of 
the adhesive is adjusted such that the aforementioned cohesion reduction 
line is formed at a temperature lower than or equal to the activation 
temperature of the hardener. 
The adhesive layer 4 is preferably admixed with electrically conducting 
particles 14 or with a small quantity of insulating particles (not shown), 
since the particles serve to maintain the layer thickness at the time of 
application of heat and pressure during the fabrication of adhesive-coated 
chips. The proportion of the conducting or insulating particles admixed in 
this case is approximately 0.1 to 30 vol %, and is set to 0.5 to 15 vol % 
in order to obtain anisotropic conductivity. The adhesive layer 4 may 
alternatively have a multilayer structure including an insulating layer 
and an electrically conducting layer formed separately from each other. In 
this case, resolution improves, permitting high-density connection of 
electrodes. 
The electrically conducting particles 14 may be metal particles of Au, Ag, 
Pt, Co, Ni, Cu, W, Sb, Sn or solder, or particles of carbon, graphite, 
etc. Further, such conducting particles or nonconductive particles, such 
as glass particles, ceramic particles or polymeric particles of plastic, 
may be used as cores, which are then coated with an electrically 
conductive layer using one of the above substances. Also, insulator-coated 
particles having electrically conducting cores coated with an insulating 
layer, or the combination of conducting particles and insulating particles 
of glass, ceramic or plastic may be used to improve the resolution. 
In order that one or more electrically conducting particles, preferably as 
many particles as possible, will be present on each fine electrode, the 
particle size of the conducting particles 14 should preferably be as small 
as 15 .mu.m or less and, more preferably, in the range of 7 to 1 .mu.m. If 
the particle size is smaller than 1 .mu.m, difficulty arises in making the 
particles contact the electrode surfaces. Also, the conducting particles 
14 should preferably be uniform in particle size, because uniform particle 
size serves to lessen the outflow of conducting particles from between 
electrodes facing each other. 
Among the aforementioned electrically conducting particles, particles 
having polymeric cores of plastic material coated with a conductive layer 
and particles of heat-fusible metal such as solder are preferably used, 
because these particles deform when applied with pressure or both heat and 
pressure, so that the area of contact with circuits increases, thus 
improving the reliability. In particular, in the case where polymeric 
cores are used, the particles do not show such a distinct melting point as 
that of solder. Thus, the softened state can advantageously be controlled 
over a wide range of connection temperatures and variations in the 
thickness or flatness of electrodes can be easily coped with. 
Where hard metal particles of Ni or W, for example, or particles having a 
large number of protuberances on their surface are used, the conducting 
particles stick into the electrodes or wiring patterns. Thus, a low 
connection resistance is achieved even if an oxide film or a contamination 
layer exists on the electrode surface, whereby the reliability can be 
improved. 
With the multi-chip mounting method according to the present invention, 
adhesive-coated chips of different sizes can be mounted as needed on a 
circuit board, thereby facilitating the mounting of a large number of 
chips on a circuit board with a small area. 
According to the present invention, since chips coated with respective 
required amounts of adhesive are used, the number of tapes with different 
widths may be small and the mounting apparatus can be simplified, as 
compared with the case of using different adhesive tapes for different 
sizes of chips. Further, unlike the case where an adhesive layer is formed 
over the entire surface of a circuit board, neither adjacent chips nor 
surrounding adhesive is adversely affected by heat or pressure, and no 
extra adhesive is used, which is advantageous from an economical 
viewpoint. 
In the preferred embodiment of the present invention, the adhesive contains 
a latent hardener, and heat treatment is performed at a temperature lower 
than or equal to the activation temperature of the hardener to obtain 
adhesive-coated chips. Accordingly, the shelf stability of the adhesive is 
improved, and a reliable multi-chip connection can be achieved at a 
temperature higher than or equal to the activation temperature. 
With the multi-chip mounting method of the invention using hydrostatic 
pressure, the pressure within the airtight vessel is kept constant, and a 
large number of MCM can be treated at the same time, whereby the mass 
production efficiency is enhanced. Also, since the heat treatment is 
carried out using gas or liquid as the medium, it is unnecessary to use 
expensive molds, and various adhesives having different properties in 
respect of heat, humidity and anaerobic characteristic can be used 
depending on the type of medium used. Further, even if the adhesive takes 
a long time to set, it is possible to produce a large number of MCM by one 
operation. 
According to the multi-chip mounting method of the present invention, a 
continuity test can be performed before the adhesive finally sets. 
Therefore, when a defective connection is discovered, the adhesive is then 
still not sufficiently set, and thus the peeling of chips and the 
subsequent cleaning operation using a solvent such as acetone can be 
carried out very easily, thereby facilitating the repair work. 
Also, by arranging groups of adhesive-coated chips on the separator in 
order of mounting on circuit boards, it is possible to improve the 
productivity. 
In the method of producing adhesive-coated chips according to the present 
invention, a cohesion reduction line is readily formed in the adhesive 
layer around the chip when the chip is heated. Since the adhesive layer 
can be peeled from the separator, a chip coated with an adhesive layer 
having a size corresponding to the chip size can be obtained relatively 
easily. By setting the heating temperature at a temperature lower than or 
equal to the activation temperature of the hardener, the adhesive-coated 
chips can be kept for later use without lowering their shelf stability. 
According to the adhesive-coated chip production method of the present 
invention, the adhesive layer is cut for at least part of its depth in the 
thickness direction by using a very simple cutting jig matching the chip 
shape, so that a chip coated with an adhesive layer having a size 
corresponding to the chip size can be obtained relatively easily. 
EXAMPLES 
Various examples according to the present invention are described in detail 
below, but it should be noted that the present invention is not limited to 
these examples alone. 
Example 1 
(1) Preparation of Adhesive Layer 
A solution containing 30% ethyl acetate was obtained by mixing, in the 
ratio of 30/70, a phenoxy resin (polymeric epoxy resin) and a liquid epoxy 
resin (epoxy equivalent: 185) containing a micro-encapsulated latent 
hardener. To this solution was added 2 vol % of electrically conducting 
particles, which were obtained by coating polystyrene particles having a 
particle size of 3.+-.0.2 .mu.m with Ni and Au in thicknesses of 0.2 .mu.m 
and 0.02 .mu.m, respectively, followed by mixing and dispersion of the 
conducting particles. The dispersion was applied to a separator 
(polyethylene terephthalate film treated with silicone; thickness: 40 
.mu.m) by means of a roll coater, and the separator applied with the 
dispersion was dried at 100.degree. C. for 20 minutes to obtain an 
adhesive film with a thickness of 20 .mu.m. 
The activation temperature of the adhesive film was measured using a DSC 
and was found to be 120.degree. C. Using a model composition from which 
the hardener had been removed, the viscosity of the adhesive layer was 
measured by a digital viscometer HV-8 (manufactured by Kabushiki Kaisha 
Reska), and was 800 poises at 100.degree. C. 
The adhesive film was cut together with the separator to obtain a tape of 2 
mm wide. 
(2) Fabrication of Adhesive-coated Chip 
The tape obtained in the manner described in (1) above was set in a chip 
mounting apparatus AC-SC450B (COB connecting apparatus manufactured by 
Hitachi Chemical Co., Ltd.) with its adhesive layer facing upward, and was 
held tense by rolls arranged in the front and at the rear of the surface 
plate in such a manner that the tape could travel in close contact with 
the surface plate. An IC chip for evaluation (2.times.10 mm silicon 
substrate having a thickness of 0.5 mm and having 300 gold electrodes 
(called bumps) of 50 .mu.m in diameter and 20 .mu.m high formed near the 
two longer sides of the substrate) was fixed to the heating head in 
position by suction. 
With the temperature of the heating head set at 110.degree. C., the tape 
was subjected to heat-pressure bonding such that its adhesive layer was 
applied with 5 kg/cm.sup.2 for 3 seconds, and then the heating head was 
raised to release the tape from pressure and separated from the surface 
plate. The actual temperature of the adhesive of the tape in contact with 
the surface of the IC chip was in this case 102.degree. C. at the maximum. 
In this manner, an adhesive-coated chip with an adhesive layer, which had 
been separated from the separator and had a size nearly identical to the 
chip size, was obtained. 
Two 5.times.5 mm IC chips (tape width: 5.5 mm) and one IC chip of 10 mm in 
diameter (tape width: 10.5 mm) were prepared in a like manner, thereby 
obtaining a total of four adhesive-coated chips. These chips had different 
bump pitches, but had the same bump height and the same silicon substrate 
thickness. 
(3) Connection 
On a 15.times.25 mm glass epoxy substrate (FR-4 grade) which had a 
thickness of 0.8 mm, had copper circuits of 18 .mu.m high thereon, and had 
connection electrodes formed at terminals of the circuits at pitches 
corresponding to the bump pitches of the respective IC chips obtained in 
the manner described in (2) above, the adhesive-coated IC chips were 
arranged. After the electrodes were positioned relative to each other 
using a CCD camera, the chips were collectively connected at 150.degree. 
C. under 20 kgf/mm.sup.2 for 15 seconds. Consequently, an MCM with four 
adhesive-coated chips of substantially equal height collectively mounted 
thereon was obtained. At the time of the connection, a 
Polytetrafluoroethlene sheet of 100 .mu.m thick was interposed as a 
buffering member between the chips and the heating head. 
(4) Evaluation 
The electrodes of the individual chips could be satisfactorily connected to 
the corresponding electrodes on the substrate. Since the adhesive was 
present only in the vicinity of the chips, almost no superfluous adhesive 
could be observed on the surface of the substrate. Further, one MCM could 
be obtained within one minute. 
Example 2 
IC chips were mounted on a substrate in substantially the same manner as in 
Example 1, but the adhesive-coated chips were produced by a different 
method. Specifically, a pressure head provided with a cutting jig was 
used, and the tape used had a width of 10 mm. For the 2.times.10 mm chip, 
for example, a heater wire comprising a nichrome wire and arranged so as 
to extend along the four sides of the chip was used as the cutting jig. 
The pressure head was not heated and was used at room temperature. Since a 
heater wire was used as the cutting jig, the tape could be cut for the 
entire depth inclusive of the separator, so that an adhesive-coated chip 
having a separator affixed to its adhesive layer was obtained. Other chips 
could also be similarly affixed with adhesive. For the chip of 10 mm in 
diameter, a looped heater wire with an inner diameter of 11 mm was used as 
the cutting jig. Also in this case, the electrodes of the individual chips 
could be satisfactorily connected to the corresponding electrodes on the 
substrate. Since the adhesive was present only in the vicinity of the 
chips, almost no superfluous adhesive could be observed on the surface of 
the substrate. 
Example 3 
IC chips were mounted on a substrate in substantially the same manner as in 
Example 2, but when producing adhesive-coated chips, the temperature of 
the heating head was set at 70.degree. C. Further, a cutting tool with a 
straight edge was used as the razor. Also in this case, adhesive-coated 
chips could be easily obtained. Since both the razor and the heating means 
were used, the adhesive could be readily transferred to the chips. 
Furthermore, the heating temperature could be set at a low temperature, as 
compared with the case of Example 1. 
Example 4 
IC chips were mounted on a substrate in substantially the same manner as in 
Example 1, but the adhesive-coated chips were producing by a different 
method. Specifically, various chips were temporarily fixed (by 
heat-pressure bonding at 100.degree. C. under 5 kg/cm.sup.2 for 3 seconds) 
beforehand on a tape (width: 10.5 mm) so that the chips could be 
continuously fed in order, as shown in FIG. 7A, and adhesive-coated chips 
each with an adhesive layer, which had been separated from the separator 
and had a size nearly identical to the corresponding chip size, were 
obtained in the same manner as in Example 1. In this case, the adhesive 
could be easily peeled from the separator, and since the chips were 
prepared in order of mounting, the productivity was extremely high. The 
electrodes of the individual chips could be satisfactorily connected to 
the corresponding electrodes on the substrate. 
Example 5 
Adhesive-coated chips obtained in the same manner as in Example 4 were 
again temporarily fixed on a continuous separator at intervals of 1 mm 
between adjacent chips, to obtain a series of adhesive-coated chips as 
shown in FIG. 7B. The productivity was extremely high because the chips 
could be removed from the separator in mounting order. The electrodes of 
the individual chips could be satisfactorily connected to the 
corresponding electrodes on the substrate. Also, since the series of 
adhesive-coated chips could be wound on a reel with an outside diameter of 
55 mm into a compact size, the chips could be easily kept in cold storage 
after operation. The electrodes of the individual chips could be 
satisfactorily connected to the corresponding electrodes on the substrate. 
Example 6 
IC chips were mounted on a substrate in substantially the same manner as in 
Example 1, but a different adhesive was used. Specifically, when preparing 
the adhesive mentioned above, no electrically conducting particles were 
added. Also in this case, the electrodes of the individual chips could be 
satisfactorily connected to the corresponding electrodes on the substrate. 
Presumably this is because the bumps of the chips and the connection 
electrodes of the glass epoxy substrate were brought into direct contact 
with each other and were firmly bonded together by the adhesive. 
Example 7 
IC chips were mounted on a substrate in substantially the same manner as in 
Example 1, but an intermediate inspection step was additionally provided 
to inspect the electrical connection between the electrodes after the 
adhesive-coated chips were obtained. First, the adhesive-coated chips 
using the adhesive obtained according to Example 6 were heated at 
150.degree. C. under 20 kgf/mm.sup.2, and upon lapse of 2 seconds, the 
connection resistance at individual connection points was measured using a 
multimeter while the chips were kept under pressure. Similar adhesive 
coated chips were connected at 150.degree. C. under 20 kgf/mm.sup.2 for 4 
seconds, and then the substrate was removed from the connecting apparatus. 
Since in this stage the adhesive had started to set due to application of 
heat and pressure, the individual IC chips were temporarily fixed on the 
substrates. These substrates were inspected with no pressure applied 
thereto, and had one defective IC chip each. 
The defective IC chips were mechanically peeled off and new chips were 
connected in the aforementioned manner. In this case, the chips could be 
satisfactorily connected. In both cases, since the adhesives were not 
sufficiently set, the peeling of the chips and the subsequent cleaning 
operation using a solvent could be performed very easily, facilitating the 
repair work. Using the DSC, the rates of reaction of the adhesives were 
measured in terms of heat quantity, and were found to be 7% in the former 
case and 20% in the latter. 
After the connection inspection step and the repair step described above, 
the IC chips were connected at 150.degree. C. under 20 kgf/mm.sup.2 for 15 
seconds, and they showed good connection characteristics in both cases. 
After the adhesive sets, it is extremely difficult to peel off the chips 
and clean the substrate by using a solvent, but according to this example, 
repair work could be performed with ease though numerous chips were 
mounted on a small-sized substrate. 
Example 8 
IC chips were mounted on a substrate by a method similar to that employed 
in Example 1, but static pressure was utilized in the step of applying 
heat and pressure at the time of connection. 
Specifically, adhesive-coated chips were placed on a glass epoxy substrate, 
and after the electrodes were positioned relative to each other using a 
CCD camera, the substrate having the chips temporarily fixed thereon was 
set in a pressure pot for pneumatic pressure treatment at 120.degree. C. 
under 20 kg/cm.sup.2 for 30 minutes, then cooled to room temperature, and 
removed from the pressure pot. According to this example, since the 
individual chips can be applied with uniform pressure regardless of their 
heights, it is unnecessary to use a buffering member unlike Example 1. 
Also, it is possible to treat a large number of MCM at a time depending on 
the capacity of the pressure pot. 
Example 9 
IC chips were mounted on a substrate in substantially the same manner as in 
Example 1, but a polytetrafluoroethylene film (thickness: 80 .mu.m) was 
used as the separator. The obtained MCM was evaluated in the same manner 
as in Example 1, and it was found that the adhesive could be transferred 
to the surfaces of the chips in more exact shape matching the chip size 
especially at the edges. Presumably this is because the separator was more 
flexible than that used in Example 1 and thus the adhesive could be cut 
sharply along the edges of the chips. The elasticity modulus of the 
polyethylene terephthalate film was 200 kgf/mm.sup.2, while the elasticity 
modulus of the polytetrafluoroethylene film was 40 kgf/mm.sup.2. 
Example 10 
IC chips were mounted on a substrate in substantially the same manner as in 
Example 1, but the adhesive-coated chips were produced with a silicone 
rubber sheet of 0.5 mm thick interposed between the separator and the 
surface plate. In this case, the adhesive could be transferred to the 
surfaces of the chips in more exact shape matching the chip size than in 
Example 1, especially at the edges. This is presumably because the 
silicone rubber sheet served as a cushioning member. Also in the case 
where a soft rubber layer exists under the separator, the thickness of the 
adhesive layer formed on the electrode surface is controlled by the 
heights of the bumps and the electrically conducting particles. Therefore, 
the bumps each had an adhesive layer of about 4 .mu.m thick formed thereon 
and the region other than the bumps had an adhesive layer of about 20 
.mu.m thick formed thereon, which thickness is identical to the original 
thickness. 
Comparative Example 
Following the method of mounting IC chips on a substrate employed in 
Example 1, the adhesive film with the separator was cut into pieces 
corresponding in shape to respective chip sizes, and the cut pieces were 
affixed to the respective electrode surfaces. Since the chips were small, 
it took much time to affix the cut pieces accurately to the chips. More 
than twenty minutes were required to obtain one MCM, and thus the 
efficiency was low compared with Example 1 in which one MCM could be 
produced within one minute. 
As is clear from the above description of the examples and the comparative 
example, according to the present invention, the adhesive layer can be 
formed accurately on the electrode surfaces of individual chips with 
different sizes, and also multiple chips of different sizes can be mounted 
at a time, whereby MCM can be fabricated with high efficiency.