Method of bonding bumps to leads of tab tape and an apparatus for arranging bumps used for the same

A method of bonding bumps to leads of a TAB tape comprises the steps of preparing a substrate which is provided with through-holes, each having a size which will not allow the bumps to pass therethrough, at positions corresponding to bonding positions of the leads of the TAB tape where the bumps are to be bonded; provisionally arranging the bumps at positions of the through-holes at one side of the substrate by reducing a pressure in another side of the substrate opposite to said one side thereof to such the bumps in said through-holes; disposing the substrate on which the bumps are provisionally arranged and said TAB tape in such a positional relationship that said bumps face to the bonding positions of the leads of said TAB tape; and bonding the provisionally arranged bumps to the leads at the bonding positions and an apparatus for arranging bumps in a positional relationship corresponding to bonding positions of leads of a TAB tape.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of bonding bumps of very small 
metal balls to leads of a TAB tape and an apparatus for arranging bumps 
used for the same, and in particular to a method of bonding bumps to the 
tip ends of the leads of a TAB tape for preparing a bump-bonded TAB tape 
used for TAB (tape Automated Bonding) method which is one of methods of 
connecting the electrodes of an IC chip with external leads and an 
apparatus for arranging bumps in a positional relationship corresponding 
to the lead tip ends of a TAB tape to be bonded. 
2. Description of Related Art 
A tape Automated bonding (hereinafter referred to as TAB) process is a 
method of bonding the tip ends of the leads formed in a selected pattern 
on a TAB tape to the electrodes of an IC chip via metallic bonding 
projections called as bumps. The bumps are preliminarily mounted either on 
the leads of the TAB tape or the electrodes of the IC chip and bonding of 
the TAB tape to the IC chip is performed by heating under pressure by 
means of a bonding machine. The TAB tape is usually manufactured by 
forming a film made of a synthetic resin such as polyimide, polyester and 
the like with sprocket holes or device holes, then laminating a metal foil 
on the film and thereafter etching the metal foil to form a lead wiring 
pattern by a photo-resist method. 
On the other hand, the bumps through which the TAB tape is connected with 
the electrodes of semiconductor chips such as ICs and LSIs and the like 
are often formed on Al electrodes of the semiconductor chips by a plating 
technique as described in Electronic Part and Materials Vol. 28, No. 7 
1989, July, pages 66-76. However, forming bumps on Al electrodes of ICs or 
LSIs by plating technique costs high and has the possibility of giving 
damages to the circuits of the semiconductor chip. Therefore, it is not 
always a preferable process. 
One of the methods of forming bumps on the leads of the TAB tape, is 
disclosed in the Japanese Unexamined Patent Publication No. JP-A-62-28623 
and another one, i.e. "a bump transferring method" is described in 
National Technical Report vol. 31 (1985) No. 3, pages 116-124. The latter 
method comprises the steps of preliminarily placing bumps on a glass 
substrate in a predetermined arrangement and transferring the bumps to the 
leads formed in a selected pattern on a TAB tape. 
However, the bump-bonded TAB tapes manufactured by the above methods are 
not necessarily adequate in view of bonding of the bumps to the electrodes 
of IC chip, because the bumps are often made in a rectangle-like shape. 
That is, such TAB tapes involve a problem that the bumps are sometimes 
bonded to the electrodes of IC chip with variety or less reliability due 
to the rectangle-like shape, unless the heights of the bumps are 
accurately equal. Further, since the bumps are formed by plating, there is 
a restriction such that the material of the bumps must be selected from 
those alloys or metals which are readily worked by plating. 
Spherical bumps are advantageous in view of bonding purpose since they are 
more deformable than conventional rectangular bumps formed on a glass 
substrate or the like by plating. However, the spherical bumps involve a 
problem of how to efficiently arrange the bumps at selected positions and 
how to readily transfer the bumps to the leads on the TAB tape, since the 
spherical bumps are manufactured separately before arrangement of the 
bumps at positions, in contrast to the rectangular bumps which are first 
formed at selected positions by plating. 
SUMMARY OF THE INVENTION 
It is a first object of the present invention to provide a method of 
bonding bumps to the leads of a TAB tape in an efficient and reliable 
manner without the above-mentioned problems. 
It is a second object of the present invention to provide a bump arranging 
apparatus for arranging bumps in a positional relationship corresponding 
to the bonding positions of the leads of a TAB tape to be bonded with the 
bumps and adapted to be used for the above-mentioned method. 
According to one aspect of the present invention, a method of bonding bumps 
to leads of a TAB tape comprises the steps of preparing a substrate which 
is provided with through-holes, each having a size which will not allow 
the bumps to pass therethrough, at positions corresponding to bonding 
positions of the leads of the TAB tape where the bumps are to be bonded; 
provisionally arranging the bumps at positions of the through-holes at one 
side of the substrate by reducing a pressure in the other side of the 
substrate opposite to said one side thereof to suck the bumps in said 
through-holes; disposing the substrate on which the bumps are 
provisionally arranged and said TAB tape in such a positional relationship 
that said bumps face to the bonding positions of the leads of said TAB 
tape; and bonding the provisionally arranged bumps to the leads at the 
bonding positions. 
According to another aspect of the present invention, an apparatus for 
arranging bumps in a positional relationship corresponding to bonding 
positions of leads of a TAB tape comprises a substrate which is provided 
with through-holes, each having such a size that the bumps to be bonded 
are not allowed to pass, in a positional relationship corresponding to 
bonding positions of the leads of the TAB tape; and pressure reducing 
means including a pressure reducing chamber disposed on a rear side of 
said substrate opposite to a front side of said substrate on which the 
bumps are to be arranged for reducing a pressure on the rear side to a 
pressure lower than that on the front side so that the bumps are sucked to 
said through-holes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The TAB process is, as mentioned in hereinbefore, a method of bonding the 
tip portions of leads, which are formed on a TAB tape in a given pattern, 
to the electrodes of an IC chip via bonding metal projections which are 
called as bumps. The present invention is relating to a method of bonding 
bumps to the leads on the TAB tape for manufacturing bump-bonded TAB tapes 
used for the TAB method and in particular, the bonding step is made easier 
by provisional arrangement of the bumps on a substrate in advance. A 
process in which a bump-bonded TAB tape is manufactured by using 
provisional arrangement of the bumps and then the leads on the TAB tape 
are bonded to the electrodes of the IC chip through the bumps will be 
briefly described with reference to FIG. 1. 
As shown in FIG. 1, a TAB tape 12 having a base film 2 and leads 3 which 
are to be bonded to the electrodes of an IC chip 1 and a substrate 5 on 
which very small metal balls 4 are provisionally arranged are arranged in 
a given positional relationship. The metal balls 4 forming bumps are 
disposed on a multiplicity of through-holes which are formed in the same 
positional relationship as that of the tip ends of the leads of the TAB 
tape. The metal balls called as bumps are transferred and bonded to the 
tip ends of the leads of the TAB tape from the substrate so that a 
bump-bond TAB tape is manufactured in a first bonding step. Then, the 
leads of the bump-bonded TAB tape are bonded to the electrodes of an IC 
chip via the bumps by means of a bonding machine in a second bonding step. 
The alignment between the leads of the bump-bonded TAB tape and IC chip is 
automatically or manually achieved by means of a TAB bonding machine and 
then, the bump-bonded TAB tape is subjected to heating under pressure by a 
bonding tool so that the leads on the tape are bonded to the electrodes of 
the IC chip. The TAB tape per se comprises a multiplicity of frames (one 
for each IC chip) which are consecutively formed in a longitudinal 
direction thereof. The leads are usually plated with copper, gold or tin 
and arrayed in a given pattern on an insulative tape made of polyimide and 
the like. Generally, tapes each wound around a reel are commercially 
available. The reel is mounted to the bonding machine at the bonding 
process. When one frame of the tape rewound from the reel is positioned at 
a bonding stage, the leads on the frame are aligned and then bonded to the 
electrodes of an IC chip. 
Since the bumps are conventionally formed, in most cases, on the IC chip, 
the leads of the TAB tape do not have the bumps. In contrast to this, the 
concept of the bump-bonded TAB tape is to use IC chips having no bumps and 
in stead of this, to preliminarily form bumps on the leads of TAB tape. 
The present invention is relating to a method of manufacturing bump-bonded 
TAB tapes. The bumps are bonded to the leads of the TAB tape by 
conveniently using a thermal pressure bonding effected by urging a heated 
bonding tool upon the bumps in a manner similarly to the bonding of the 
leads to the IC chip electrodes, by using the same. In other words, a reel 
around which a TAB tape having no bumps is wound is mounted on the bonding 
machine and then spherical bumps are bonded to the tip ends of the leads 
at its bonding stage. 
The bonding stage of the bonding machine generally comprises a bonding 
platform on which an IC chip is provisionally placed and fixed thereto and 
a frame-like fixture which pressures the TAB tape against the platform. A 
mechanism for correcting the relative misalignment therebetween is 
combined with the bonding stage. In order to bonding the bumps to the 
leads of the TAB tape by conveniently using such a mechanism of the 
conventional bonding machine in accordance with the present invention, it 
is necessary to remove the bonding stage, in particular, the bonding 
platform on which the IC chip is placed from the bonding machine and to 
arrange bumps there in a pattern corresponding to the lead pattern of the 
TAB tape. In other words, the transfer or bonding of the bumps to the 
leads of the TAB tape can be achieved by using the mechanism of the 
bonding machine as it is if the arrangement of bumps in a given pattern is 
realized on the bonding platform. 
It is necessary to prepare bump-bonded TAB tapes of high quality in order 
to provide excellent bonding between the leads of the TAB tape and the 
electrodes of the IC chip on the secondary bonding. In order to achieve 
this, the performance of an arrangement substrate on which bumps are 
preliminarily arranged to be used for the second bonding is important. 
One embodiment of a method of bonding bumps to the leads of a TAB tape will 
now be described with reference to the drawings. A vacuum suction chamber 
11 corresponding to a bump suction and provisionally fixing portion 
disposed on a bonding platform is shown in FIG. 2A. The suction chamber 11 
has on the upper side thereof a thin flat plate 5 which is provided with 
through-holes 13 in positions at which bumps are to be arranged. The plate 
5 is corresponding to the arranging substrate 5 of FIG. 1. The 
through-holes 13 are in communication with a suction port 14 via the 
vacuum suction chamber 11 as shown in a sectional view of FIG. 2B. 
Although the suction chamber is made in a form of tunnel extending along 
the through-holes and communicated with the suction port 14 as shown in 
FIG. 2B, the suction chamber may be a hollow box-like member including a 
thin flat plate 5 having through-holes thereon if the upper flat plate 
provided with through-holes has a sufficient thickness so as to prevent it 
from being deformed by heat-bonding. The flat plate 5 should be made of 
material which can provide an even flat surface and can be machined for 
forming fine through-holes and hardly changes its properties due to heat 
and pressure applied on bonding. A thin plate of stainless steel, nickel 
and the like or ceramics and the like is suitable for the material of the 
flat plate 5. 
Then, the vacuum suction chamber 11 which is evacuated via the suction port 
14 is located in the vicinity of a bump supply mechanism including a tray 
15 on which a multiplicity of bumps 4 are placed as shown in FIG. 3A so 
that the bumps 4 are sucked and attracted to the through-holes 13 as shown 
in FIG. 3C. This step is illustrated, in the figure, so as to attract 
bumps upward by placing the suction chamber upside down and moving it 
downward to approach the bump. It is possible to adopt a method in which 
the bumps are dropped upon the upper side provided with the through-holes 
of the chamber which is located normally or slantingly. 
The suction chamber 11 on which bumps are sucked and preliminarily fixed is 
disposed on the bonding platform of the bonding machine as shown in FIG. 
3C. An alignment between a TAB tape 12 having leads 3 formed on a film 
base made of an insulative material such as polyimide and the like and the 
suction chamber 11 is performed by using an alignment adjusting mechanism 
(not shown). After completion of the alignment, a bonding tool 17 which is 
heated to a suitable temperature is driven to impose a given pressure upon 
the tape 12, resulting in that the bumps provisionally fixed on the 
through-holes of the suction chamber 11 are transferred and bonded to the 
leads of the TAB tape. 
The suction chamber 11 from which bumps have been transferred is again 
returned to a step of FIG. 3A in which bumps are sucked for the next 
cycle, and simultaneously, the TAB tape is advanced by one frame on the 
bonding machine and a next frame of the tape is brought into a stand-by 
position similarly to the previous cycle. It can be understood that the 
above-mentioned steps provide an efficient method of successively bonding 
the bumps to the leads on respective frames of the TAB tape which is 
rewound from the reel. 
FIG. 4 shows another embodiment of the vacuum suction chamber. A plurality 
of thin flat plates 5 having through-holes 13 are arranged along the 
circumference of a vacuum suction chamber portion 11 which is formed into 
a shape of polygon so that bump suction and provisional fixing portions 
are defined thereon. Each of the flat plates 5 forms a bump fixing element 
which plays a role of suction and fixing of one set of bumps to be 
arranged. The vacuum suction chamber 11 is mounted on a bonding platform 
of a bonding machine so that the top side of the suction chamber is 
located at a position where the conventional bonding platform is to be 
provided. Although the suction chamber 11 having eight bump fixing 
elements is exemplarily illustrated in the drawing, it is of course that 
the number of the elements may be changed if desired. While rotating 
stepwise the polygonal suction chamber 11 around a shaft 14 also serving 
as suction port, the suction chamber 11 sucks bumps 4 to the through-holes 
thereby provisionally fixing them on one of the flat plates 5 which comes 
the bottom position near a bump supply station including a tray 15 on 
which the bumps 15 are placed and a bump automatic supply machine 20 in 
this case. When the one flat plate of the suction chamber on which the 
bumps are placed comes to the top position, i.e. an upper bonding station, 
the TAB tape leads are aligned with the bumps fixed on the one flat plate 
and then the bumps are transferred and bonded to the leads 3. After 
completion of bonding of the bumps to the leads in one frame of the TAB 
tape, the suction chamber is rotated by one unit and the TAB tape is 
advanced by one frame and simultaneously, bumps are supplied from the 
automatic supply machine. By performing a series of successive operations 
as mentioned above, transfer and bonding of the bumps to the leads of the 
TAB tape can be achieved in a very efficient manner. 
In the present embodiment, the vacuum suction chamber having through-holes 
is used to arrange the bumps necessary for one frame of the TAB tape into 
a given pattern. This makes it possible to smoothly arrange under a 
sucking force soft metal balls which otherwise readily cause problems such 
as crushing and contamination. Further, it has become possible to 
precisely and efficiently bond bumps to the tip ends of the leads of the 
TAB tape by effectively using main components of a conventional TAB 
bonding machine and by merely replacing a vacuum suction chamber for the 
bonding platform. 
TEST 1 
A vacuum suction chamber 11 as shown in FIG. 2A was made of stainless 
steel. A flat plate 5 having through-holes applied to the upper side of 
the box was made of stainless steel plate of 30 .mu.m thickness. The 
through-holes are made by an etching process. Each through-hole has a 
diameter of 60 .mu.m. Fifty through-holes were formed along each of four 
sides and total 200 through-holes along four sides were formed in a shape 
of a square having four sides, each 10 mm long. 
Gold balls, each having a diameter of 80 .mu.m were used as bumps 4. A 
multiplicity of gold balls were placed on the tray 15. The vacuum suction 
chamber was brought close to and above the tray 15 so that the gold balls 
were sucked and fixed to the openings of the through-holes. 
The TAB tape 12 was formed so that the tip ends of the leads were aligned 
with the through-holes of the flat plate and the gold plated copper leads 
3 were formed on a polyimide film 2. This tape was preliminarily set in 
the TAB inner lead bonding machine. One frame of the tape was set on the 
bonding stage of the bonding machine. Then, the suction chamber 11 having 
the bumps 4 provisionally fixed on the through-holes 13 was moved to the 
bonding platform portion of the bonding machine while the suction chamber 
portion 11 was evacuated. After the tape was adjusted so that the leads 
were positioned in alignment with the positions of the gold balls on the 
suction chamber, the bonding tool 17 which was heated at 450.degree. C. 
was lowered upon the tape. Bonding was performed under a pressure of 3 kgf 
(15 gf per one lead) for five seconds. 
This caused all gold balls provisionally fixed on the through-holes of the 
flat plate to be precisely transferred and bonded to the tip ends of the 
leads of the TAB tape one by one. After bonding, the strength of bonding 
of the gold balls upon the TAB tape was measured by the shear test method. 
It was found that every lead stably holds a bonding strength not less than 
1.5 gf per one lead which is enough to function as a TAB tape with bumps. 
TEST 2 
A vacuum suction chamber 11 having an octagon shape as shown in FIG. 11 was 
manufactured. The dimension and arrangement of the through-holes 13 of 
each bump fixing element was identical to those of Test 1. However, the 
flat plate 5 having the through-holes was made of nickel plate having a 
thickness of 30 .mu.m manufactured by an electroforming method. As shown 
in FIG. 5, the vacuum suction chamber was incorporated in the bonding 
platform of the TAB inner lead bonding machine. A rotary shaft having at 
one end a suction port was connected with a vacuum pump. A tray 15 on 
which a multiplicity of bumps of gold balls 4 of 80 .mu.m were placed was 
disposed below the vacuum suction chamber. The gold balls were 
automatically replenished to the tray from a supply machine 20 when they 
were used and reduced. The upper portion of the vacuum suction chamber was 
corresponding to the bonding platform and intermittently rotated by 45 
degrees in one pitch. Whenever the suction chamber is stopped in any 
position, the upper side thereof was adjusted so that it was in a 
precisely parallel relation-ship with the tip end face of the bonding tool 
17. 
One frame of the TAB tape 12 having the leads 13 corresponding to the 
pattern of the arranged through-holes of the flat plate was set on the 
bonding stage similarly to TEST 1. Gold plated leads made of copper were 
also used in this TEST. When evacuation of the vacuum suction chamber was 
commenced, the gold balls on the tray were sucked and provisionally 
secured to the openings of the through-holes on the lower side of the box. 
Then, the vacuum suction chamber was rotated by only 45 degrees of one 
pitch, so that the gold balls were sucked and provisionally fixed to the 
through-holes of the second element. After rotation of the suction chamber 
by four pitches, the first element having the gold balls provisionally 
fixed thereto was advanced to a normal position of the bonding platform. 
In this position, alignment of the leads of the TAB tape with the balls 
was performed and bonding of the balls to the leads of the tape was 
performed under a pressure of 3 kgf for 0.5 second by means of a bonding 
tool 17 heated to 450.degree. C. All gold balls having been provisionally 
secured to the openings of the through-holes of the flat plate were 
transferred and bonded to the respective leads of the TAB tape in 
position. 
It is found from this TEST that the bonding strength between the bonded 
gold balls and the leads is also stably maintained at a value not less 
than 1.5 gf so that the performance of the TAB tape having bumps can be 
sufficiently satisfied. 
TEST 3 
A TAB tape having tin plated leads made of copper which was also used like 
TEST 2. Bonding conditions of this TEST were same as those of TEST 2 
except that the heating temperature of the bonding tool was 300.degree. C. 
Also in this TEST, all gold balls were reliably transferred and bonded to 
the tip ends of the TAB tape leads. The bonding strength is stably 
maintained at a value not less than 0.7 gf although it is slightly lower 
than that of the gold plated tape. 
TEST 4 
A 16-side polygon suction chamber 11 as shown in FIG. 6 was used. The 
material and size of the flat plate 5 and the size and arrangement of 
through-holes 13 of each bump fixing element were same as those of TEST 2. 
A bump supply mechanism was different from both of the previous TESTs and 
arranged to include a bump supply 18, a bump receiving tray 19 and a bump 
returning feeder 21 for returning excess bumps received by the tray 19 as 
shown in FIG. 6. By the arrangement, it was possible to sprinkle the bumps 
over the flat plate located in the upper-lateral side of the suction 
chamber from the bump supply 18. The sprinkled bums 4 were trapped by the 
openings of the through-holes on the flat plate and provisionally secured 
thereon. Excess bumps were dropped upon the bump tray 19 located below 
after all the openings of the through-holes have been occupied by the 
bumps and then conveyed to the bump supply 18 again. 
If a large size polygonal suction chamber used in the TEST 3 is used in the 
previous TEST 2, the bump suction force may be weakened since air would be 
introduced through unoccupied openings of the through-holes of the flat 
plate until next bumps are sucked after transferring of the original 
bumps. Since the through-holes are small, a vacuum pump having an enough 
capacity can generate a sucking force enough to suck the bumps even when 
the through-holes are partially unoccupied. However, if the capacity of 
the pump is low and/or the drum of the suction chamber becomes larger, the 
vacuum leakage via the free through-holes is not negligible. It is 
effective to close the free through-holes by an elastic rubber belt 23 and 
pulleys 22 in such a case. It is confirmed that the bump supply mechanism 
formed in this TEST can maintain a sufficient bump sucking force. 
In the above-mentioned TESTs, the flat plate on which the bumps are 
arranged is placed on the bonding platform of the bonding machine and the 
leads of the TAB tape are aligned with the bumps. Thereafter, bonding of 
the bumps to leads is carried out by applying a pressure under suitable 
conditions by means of heated bonding tool. At the next step, it is 
necessary to separate the leads to which the bumps are bonded from the 
flat plate having the through-holes together with TAB tape. If the 
evacuation condition when the bumps are sucked remains on the opposite 
side of the flat plate, the bonded bumps may be separated from the leads 
in the course of removal of the TAB tape in some cases since the bumps are 
continuedly sucked by the vacuum sucking force. 
A term "vacuum" used herein means an evacuated state which causes a 
pressure difference sufficient for sucking small metal balls serving as 
bumps to through-holes formed in a flat plate. Practically the degree of 
vacuum which can be readily obtained by a small diaphragm pump, magnet 
pump, rotary pump and the like is generally satisfactory. 
It is confirmed by the inventors' study that a suction force in the order 
of about 1 gf is applied to one bonded bump having a diameter of 80 
microns when the rear side of the flat plate having 200 through-holes, 
each being 70 microns in diameter is maintained at a reduced pressure 
lower than the atmospheric pressure by one atm. by means of a diaphragm 
pump. This suction force is substantially equal to the bonding force 
between a bump and a lead which are thermally bonded. It is found that 
when the flat plate having 200 through-holes is additionally formed with a 
through-hole having a diameter of 70 microns and a vacuum sucking force 
applied to the 200 through-holes is similarly measured under a condition 
that this additional through-hole is opened while the 200 through-holes 
are closed, the suction force per bump is reduced to about 0.1 gf. Even if 
the additional through-hole remains opened, no difficulty occurs in the 
operation for sucking the bumps on the 200 through-holes. 
It is understood from the foregoing that there is a possibility that some 
bumps will be separated from the leads once bonded thereto if the TAB tape 
is forcedly removed while the space below the rear side of the flat plate 
is left evacuated after bonding the bumps to the leads. In order to avoid 
this separation, it is effective to reduce the vacuum degree at the rear 
side of the flat plate immediately prior to advancing of the TAB tape 
after completion of transferring of the bumps for one frame or 
alternatively to form a small hole in the flat plate or the vacuum chamber 
and leave it opened at least if the vacuum degree is maintained. 
When a condition which provides greater deformation of the bumps is adopted 
on bonding, it is useful to apply a force to the bumps so as to forcibly 
separate the bumps from the through-holes by positively increasing the 
pressure in the vacuum chamber to a value higher than the atmospheric 
pressure in addition to introducing air into the chamber. This will 
achieve a more reliable separation of the TAB tape from the flat plate. 
Since this method of increasing the inner pressure in the chamber each 
time when the transfer of the bumps to one frame of the TAB tape is 
completed may also provide an effect that deposition gradually piles up on 
the flat plate around the through-holes can be cleaned, this method is 
advantageous for mass production. 
When a switching operation of a change-over valve in a path between the 
vacuum chamber and an exhaust system is interlinked with the periodical 
operation of the tool and the like of the bonding step in the 
above-mentioned process, a bump transfer can be realized as a more 
reliable and efficient process. 
Five embodiments 1 through 5 based on the above-mentioned concept will be 
described with reference to the drawings. 
EMBODIMENT 1 
As shown in FIG. 8, a vacuum chamber 11 which is evacuated by a vacuum 
exhaust system 40 is disposed so that it is positioned below a bonding 
tool. The upper portion of the vacuum chamber 11 is made of a flat plate 5 
which are formed with through-holes 13 in positions at which bumps are to 
be sucked. A change-over valve 30 is disposed between the vacuum chamber 
11 and the vacuum exhaust system 40 so that air is selectively introduced 
into the chamber 11. 
FIG. 8A shows that air is evacuated from the vacuum chamber 11 via the 
change-over valve 30 and that bumps 4 are sucked to the through-holes of 
the flat plate by the suction force. The relative positional relations 
among a TAB tape which is a laminate of gold plated copper leads 3 and a 
polyimide film 2, the vacuum chamber 11 on which bumps 4 are arranged and 
the bonding tool 17 can be precisely controlled by means of adjusting 
mechanism (not shown). Each of the through-holes 13 in the flat plate is 
60 .mu.m in diameter. Gold balls of 80 .mu.m are used as bumps and a TAB 
tape having 200 leads each having a width of 60 .mu.m are used. 
When a pressure is applied upon the leads at 10 gf per lead by lowering the 
bonding tool which is heated to 450.degree. C., bonding between each lead 
3 and bump 4 is performed (FIG. 9B). Then, the pressure in the vacuum 
chamber is increased to an atmospheric pressure by operating the 
change-over valve 30 as shown in FIG. 8C. Then the bumps 4 are separated 
from the through-holes 13 and are completely transferred to the leads 3 
(FIG. 8D). Transferring of the bumps to one frame of the TAB tape is 
completed by the above-mentioned steps. Accordingly, the vacuum chamber 11 
is evacuated again by operating the change-over valve 30 to return to the 
bump suction step for repeating the next cycle. 
When the tape is removed by lowering the vacuum chamber 11 while the vacuum 
chamber 11 is continuedly evacuated without operating the change-over 
valve 30 after completion of bonding step in the above-mentioned process, 
some of the bonded bumps 4 may be separated from the leads 3 so that more 
than half of bumps remain sucked on the through-holes 13 or scattered 
around the through-holes. In contrast to this, such a problem never occurs 
in the present embodiment so that very stable transfer of bumps can be 
conducted. 
It is confirmed that no problem occurs even if the timing at which air is 
introduced into the vacuum chamber 11 is varied over a wide range. Even 
when an air is introduced into the vacuum chamber by operating the 
change-over valve 30 at a step of FIG. 8A, that is prior to a step at 
which the bonding tool is lowered after alignment of the bumps 4 on the 
through-holes 13 with the leads is completed, the bumps 4 which have been 
once arranged on the flat plate 5 are held there and all bumps are 
transferred to proper positions of the leads. In other words, timing of 
operating the change-over valve 30 is not critical and may be at any time 
during an interval before the TAB tape is separated after bonding and 
after alignment of the arranged bumps with the TAB tape is completed. 
EMBODIMENT 2 
Although an apparatus which is the same as that of the embodiment 1 is 
used, a change-over valve is not disposed between the vacuum chamber 11 
and the vacuum exhaust system 40 and in stead of that a normally opened 
small hole 28 is formed to the vacuum chamber 11 disposed at the rear side 
of a flat plate 5 having through-holes 13. The diameter of the 
through-holes 13 on the flat plate is 60 .mu.m, gold balls of 80 .mu.m are 
used as bumps and a TAB tape having 200 leads each having a width of 60 
.mu.m is used similarly to the embodiment 1. 
FIG. 9A shows a step at which the TAB tape having the leads 3 formed on a 
polyimide film 2 is disposed below a bonding tool 17 after the bumps 4 are 
sucked upon the through-holes 13 of the flat plate 5, and alignment 
between the leads 3 and the bumps 4 is completed by an alignment mechanism 
(not shown). Although the small hole 28 is opened, small size bumps 4 are 
sucked in the openings of the through-holes 13 of the flat plate 5 without 
causing any problem. 
Then, pressure bonding is performed at a pressure of 10 gf per lead by 
lowering the bonding tool 17 which is heated to 450.degree. C. as shown in 
FIG. 9B. Then, the bonding tool is returned to an original stand-by 
position (FIG. 9C), and thereafter the TAB tape is separated by lowering 
the vacuum chamber 11 and all the bumps are transferred to the leads of 
the tape as shown in FIG. 9D. The next bumps are sucked to the 
through-holes 13 of the flat plate 5 after advancing the TAB by one frame. 
The process is thus returned to the step of FIG. 9A. 
EMBODIMENT 3 
A pressure increasing mechanism is incorporated into the apparatus of the 
embodiment 1 to provide an arrangement shown in FIG. 10A. A reference 
number 50 denotes a pressurized air cylinder of which an outlet pressure 
is adjusted to 0.5 atm and a reference numeral 45 denotes a valve for 
opening and closing a passage of pressurized air. The sizes of a flat 
plate 5, through-holes 13, bumps 4 and TAB tape are all same as those of 
the embodiment 5. 
Operation from the step of alignment between the bumps and the TAB tape 
leads (FIG. 9A) to the step of bonding of the bumps to the leads by 
lowering the bonding tool (FIG. 10B) is identical with that of the 
embodiment 1. However, the heating temperature of the bonding tool is 
420.degree. C. and the bonding pressure is 15 gf per lead. When, the 
bonding tool begins to lift up for returning to the stand-by position, the 
change-over valve 30 is operated simultaneously to close a passage between 
the vacuum chamber 11 and the suction system 40 and communicate the 
pressurized air cylinder 50 with the vacuum chamber 11 (FIG. 10C). 
Subsequently, the valve 45 for pressurized air is opened so that air is 
introduced in the vacuum chamber 11. 
In this case, the TAB tape is forcibly separated from the flat plate before 
lowering the vacuum chamber 11 while all the bumps are transferred to the 
leads of the tape. 
EMBODIMENT 4 
A projection 32 is provided to the side of a bonding tool 17 as shown in 
FIG. 11A. A change-over valve 31 disposed in a passage communicating the 
vacuum chamber 11 with an evacuation system 40 operates automatically to 
take a first position as shown in FIG. 11A or a second position as shown 
in FIG. 11B by a switch 33 actuated by the projection 32 and a control 34. 
When the switch 33 is depressed by the projection 32, the change-over 
valve takes the second position so that the vacuum chamber is 
discommunicated from the evacuation system and the outside air is allowed 
to leak into the vacuum chamber through the valve thereby to increase the 
pressure in the vacuum chamber 11 as shown in FIG. 11B. When the 
projection 32 is separated from the switch 33, the change-over valve takes 
the first position so that the vacuum chamber 11 is communicated with the 
evacuation system thereby evacuating the vacuum chamber as shown in FIG. 
11A. 
The bonding tool 7 stops in the upper stand-by position during a time 
interval when the vacuum chamber having the through-holes 13 of the flat 
plate 5 on which the bumps are sucked is set at the bonding position and 
the bumps are aligned with the leads 2 of the TAB tape. Accordingly, the 
change-over valve 31 is at the first position so that the vacuum chamber 
11 is communicated to the evacuation system 40 (FIG. 11A). When the 
bonding tool 17 is lowered to commence the bonding step, the projection 32 
provided to the side of the bonding tool 17 actuates the switch 33 so that 
the change-over valve 31 takes the first position so that the vacuum 
chamber is discommunicated from the evacuation system 40 through the 
control 40 and simultaneously communicated to outside thereby to introduce 
atmospheric pressure into the vacuum chamber 11 (FIG. 11B). The TAB tape 
having the leads 3 to which the bumps are transferred is separated from 
the flat plate 5 by lowering the vacuum chamber 11 before the time when 
the bonding tool is lifted up again thereby to cause the change-over valve 
31 to take the first position for commencing evacuation of the vacuum 
chamber 11. In this embodiment, all of the 200 bumps are reliably 
transferred to the leads, resulting in an excellent bonding. 
EMBODIMENT 5 
In the previous embodiment 4, one of the inlets of the change-over valve 31 
is connected via an electromagnetic valve 46 to a pipe from a nitrogen gas 
cylinder 51 in which the gas pressure is adjusted to provide an output 
pressure of 0.5 atm as shown in FIG. 12A. The electromagnetic valve 46 is 
automatically actuated by a control 34 which receives a signal from a 
switch 33. The control 34 is preset in such a manner that the 
electromagnetic valve 46 is energized for introducing nitrogen from the 
cylinder 51 into the chamber 11 at two seconds after the change-over valve 
31 is actuated by lowering of the bonding tool. When the projection 32 is 
separated from the arm of the switch 33 by lifting the bonding tool, both 
of the change-over valve 31 and the electro-magnetic valve 46 are returned 
to their original positions so that the vacuum chamber 11 is evacuated 
again. 
Now operation of this apparatus will be described. When the bonding tool 17 
is in the stand-by position, the change-over valve 31 is in such a 
position that the vacuum chamber 11 is communicated with the evacuation 
system 40 and the electro-magnetic valve 46 is kept closed. When the 
bonding tool 17 is lowered so that the projection 32 actuates the switch 
33, the change-over switch 31 is actuated so that the vacuum chamber 11 is 
disconnected from the evacuation system 40 and connected with the nitrogen 
gas cylinder 51. At this stage, however, since the electro-magnetic valve 
46 disconnects the nitrogen gas cylinder 51 from the valve 31, an almost 
vacuum condition is maintained in the vacuum chamber 11. The bonding tool 
which is heated at 400.degree. C. is continuedly lowered during this 
period of time until it applies an average pressure of 15 gf to each lead 
for only 0.5 second so that a pressure bonding of the leads to the bumps 
is performed. Then, the bonding tool is moved upward. 
The electro-magnetic valve 46 is operated to communicate the vacuum chamber 
with the nitrogen cylinder in response to a signal produced from the 
control 44 by the upward movement of the bonding tool so that the pressure 
in the vacuum chamber 11 is increased. The leads which are bonded to the 
bumps are lifted up smoothly so that the TAB tape can be returned to the 
initial preset position. Then, the TAB tape is advanced by one frame to 
set a next frame so that the process can be returned to a step of FIG. 
12A. In such a manner, the operation of transfer of the bumps to the lead 
tip ends is achieved in a very efficient manner. 
When balls each having a diameter of 80 .mu.m are used in the 
above-mentioned embodiments, the through-holes of the flat plate 5 serving 
as a bump arranging substrate should be formed with a small diameter of 
about 60 .mu.m. Since it is very difficult to precisely form such small 
through-holes in a thicker substrate, the substrate must be relatively 
thinner. It is found that when the thickness of the substrate exceeds 30 
.mu.m, it is very difficult to precisely form a multiplicity of 
through-holes each being 60 .mu.m in diameter. However, if a thin flat 
plate is used, the plate could be deformed in such a manner that the 
peripheral edges of the through-holes are bent to form recesses due to 
repeated heating and application of pressure by the bonding tool in the 
step of transferring of the bumps to the TAB tape. There is a problem that 
such a deformation of the substrate causes different heights of the 
arranged bumps so that an excellent bump arrangement cannot be formed. 
In order to overcome the above-mentioned problem, a porous and 
air-permeable intermediate plate 54 of ceramics is interposed between a 
bump arranging substrate 5 which is formed with a plurality of 
through-holes 13 and a vacuum suction chamber 11 for reinforcing the 
substrate as shown in FIG. 13 in another embodiment of the present 
invention. The vacuum suction chamber 11 is connected to a suction 
apparatus (not shown) through an exhaust pipe 14. The vacuum suction 
chamber 11 is provided with groove-like opening 57 on the side facing to 
the through-holes 23 of the substrate as shown in the sectional view of 
FIG. 14. In the case of the substrate being 30 .mu.m in thickness and the 
through-holes being 60 .mu.m in diameter, an excellent result is obtained 
when the width A of the groove-like opening is 1 mm and the thickness B of 
the porous intermediate plate of ceramics is 1.0 mm. 
An embodiment in which the polygonal vacuum suction chamber of FIG. 4 is 
provided with the porous intermediate plate 54 similar to that of FIG. 14 
is shown in FIG. 15. The embodiment of FIG. 15 is identical with the 
embodiment of FIG. 4 in structure and operation except that the porous 
intermediate plate 54 is provided. 
The porous intermediate plate may be made of porous glass, porous metal, 
other than ceramics. It is not necessary to make the entire of the 
intermediate plate porous. A porous plate which is formed with small holes 
at a portion facing to the through-holes of the substrate may be used. 
The substrate is reinforced by provision of a porous plate in the bump 
arranging apparatus in this embodiment so that the substrate is 
considerably strong against a pressure from the bonding tool. Therefore, 
deformation of the substrate and formation of the recesses around the 
through-holes hardly occur so that the number of times by which the 
substrate can be used repeatedly is remarkably increased. 
Since use of the porous plate 54 enhances heat-insulating properties, the 
leakage of heat of the bonding tool to the vacuum suction portion 11 is 
greatly reduced so that transfer and bonding of the bumps can be performed 
very stably and efficiently. 
A further embodiment of a bump arranging apparatus is shown in FIG. 16. The 
bump arranging substrate is made of two nickel substrates 5a and 5b. The 
upper substrate 5a is formed with the through-holes 13 each having a 
diameter slightly larger than that of the bump at positions in which the 
bumps are to be arranged. The lower substrate 5b is formed with 
through-holes each having a diameter slightly smaller than that of the 
bump in alignment with the through-holes of the upper substrate 5a. For 
example, for the bumps of 80 .mu.m, the thickness A of the upper substrate 
5a is 60 .mu.m, the diameter C of the through-holes 13a is 100 .mu.m, the 
thickness B of the lower substrate 5b is 30 .mu.m and the diameter D of 
the through-holes 13b is 60 .mu.m. Forming the through-holes stepwise in 
such a manner can prevent a defective bump arrangement such that two bumps 
are trapped in one through-hole and/or a bump which has been sucked once 
is removed from the through-hole by vibration. 
The reason why the diameter of the through-hole 13a is slightly larger than 
that of the bump 4 is that only one bump will enter the through-hole 13a. 
Accordingly, when bumps having 80 .mu.m diameter are used like the present 
embodiment, the diameter of the through-holes 13a is preferably in a range 
of 90 to 100 .mu.m. Since the through-holes 13b play a role of sucking 
bumps into the through-holes 13a under a suction force, it will suffice to 
form the through-holes 13b smaller than the size of the bumps. The upper 
substrate 5a is formed in such a manner that a bump trapped in the 
through-hole 13a projects partially above the surface of the substrate 
12a. The bump is projected above the upper surface of the substrate 5 by 
about 7 .mu.m in the present embodiment and it is generally preferable 
that the projection height is not larger than a half of the bump diameter. 
An effect similar to that of the use of two bump arranging substrates 5a 
and 5b can be obtained by forming the through-holes 13 stepwise in one 
bump arranging substrate as shown in FIG. 17. The through-holes may be 
formed in the reversed conical shape. 
When the bumps are supplied to the bump arranging substrate, the bumps 
which are triboelectrically charged may be attracted with each other and a 
plurality of bumps may be collected in one through-hole and/or be 
attracted to positions other than the through-holes. An embodiment to 
prevent this is illustrated in FIG. 18. In this embodiment, the bumps 4 
are irradiated with ion beams from an ion generator 40, when the bumps are 
sucked to the substrate 5 of the vacuum suction chamber 11 from a bump 
supply 15. Such an irradiation with ion beams causes the bumps to be 
electrically neutrized by discharging electricities in the ionized gases 
since the bumps are transferred through ionized atmosphere to the 
substrate 5. Mutual attraction of the bumps is avoided so that collection 
of plurality of pumps in one through-hole is prevented. For example, an 
ion gun manufactured by Shimco Japan Kabushiki Kaisha may be used as the 
ion generator. Alternatively, an air injected from a compressor is ionized 
and generated ions may be blown upon the bumps. 
FIG. 19 is a view showing a further embodiment in which ion beams are 
irradiated. The bumps 4 are dropped upon an inclined substrate 120 from a 
bump supply 80 so that the bumps 4 rolls on the substrate 120. Ionized gas 
is blown to the falling bumps from an ion blower 300 (Model A300 
manufactured by Shimco Japan Kabushiki Kaisha). Since there is no mutual 
attraction among bumps in this case, a substrate which is formed at the 
bump arranging positions with recesses 130 each having a diameter slightly 
larger than that of bump traps the bumps in the recesses as shown in FIGS. 
20A and 20B so that an individual bump can be readily arranged in each 
recess without evacuation at the opposite side of the substrate. 
A bump arranging substrate which is formed with through-holes or recesses 
is used in the afore-mentioned embodiment. Laser machining, 
electroforming, precise electric discharge machining processes and the 
like are used for forming through-holes in the substrate. Even if any 
process is used, formation of round through-hole having a diameter of 60 
.mu.m is a limit of fabrication for a substrate having a practical 
thickness. It is desired that these through-holes give no damages to bumps 
made of very small size metal spheres. 
On the other hand, metal spheres each having a smaller diameter are used as 
bumps in association with increase in packaging density of semiconductors. 
For example, bumps each having a diameter less than 50 .mu.m may be 
demanded. Accordingly, precise fabrication of through-holes having a small 
diameter is demanded for a bump arranging substrate used for these small 
bumps. As the bumps become smaller in size, the possibility that small 
burrs remained at the peripheral edges of the through-holes are 
obstructive to transferring of the bumps to the TAB tape becomes larger. 
Therefore, smoothing the peripheral edges of the through-holes is strongly 
demanded for a bump arranging substrate in addition to forming small 
through-holes. 
In order to achieve this, it is effective in formation of the through-holes 
to reduce the diameter of the through-holes which are initially formed 
with a diameter slightly larger than the desired diameter to a desired 
diameter by plating on the walls thereof. A known chemical nickel plating 
method can be used for the plating. 
There are varieties of the bump arranging substrates such as a substrate 
which is formed, in order to use a thicker material, with two stepped 
through-holes having a larger diameter on the side where bumps are 
arranged and a smaller diameter on the opposite side where evacuation is 
performed, a substrate which is formed, in order to prevent a plurality of 
bumps from collecting in one through-hole, with through-holes having a 
smaller diameter on the right side and a larger diameter on the opposite 
side and a substrate formed with through-holes each having a diameter of 
the intermediate portion smaller than those on both sides so that both 
effects are combined. The after-mentioned plating method may be 
effectively used for any type of substrate. 
TEST 5 
Bump arranging substrates each having a thickness of 0.1 mm made of 
stainless steel are used for bonding gold bumps on the leads of a TAB tape 
used for packaging an IC chip having a total 200 electrodes in 140 .mu.m 
pitch along peripheral four sides. Two kinds of arranging substrates are 
used. Each of No. 1 series substrates 1 is a conventional substrate (as a 
control) which is formed with 200 through-holes each having a diameter of 
60 .mu.m in a pattern corresponding to that of the electrodes of the chip 
by the electric discharge machining method. Each of No. 2 series 
substrates 2 of the present embodiment is formed with through-holes having 
a diameter of 65 .mu.m by the precise electric discharge machining and 
then coated with nickel by the chemical plating method so that the inner 
diameter of the through-holes is reduced to 60 .mu.m, which is the same as 
that of the through hole of the substrate 1. 
Bonding of the bumps to the leads of the TAB tape (primary bonding) is 
performed by using these two kinds of substrates and small metal spheres 
of 80 .mu.m diameter as bumps. The bonding conditions of both kinds of 
bumps are such that the temperature of the tool is 500.degree. C. and the 
applied pressure is 20 gf/lead. Primary bonding of 20 frames of each of 
substrates 1 and 2 is conducted. 
The results of the test are shown in Table 1. Primary bonding shows 
different bonding rates between the two series of the substrates 1 and 2. 
Bumps are not completely bonded to leads in some of No. 1 series of the 
substrates 1. This is due to a fact that the bumps are trapped by the 
burrs around the through-holes of the substrates 1 and not smoothly 
removed therefrom. Such a problem never occur for No. 2 series of the 
substrates 2. Very stable primary bonding is conducted. 
It is understood from above test that the primary bonding rate i.e. the 
ratio of the number of bumps which are reliably bonded to the leads to the 
total number of the bumps in one frame, is improved even when the 
substrate of this embodiment is formed with through-holes having the same 
size as that of conventional substrate. 
TABLE 1 
______________________________________ 
Bump Bonding 
No. Substrate diameter rate (%) 
______________________________________ 
1 Substrate 1 80 .mu.m 100.0 
(control) 
2 Substrate 1 " 100.0 
(control) 
3 Substrate 1 " 99.0 
(control) 
4 Substrate 1 " 100.0 
(control) 
5 Substrate 1 " 100.0 
(control) 
6 Substrate 1 " 98.5 
(control) 
7 Substrate 1 " 100.0 
(control) 
8 Substrate 1 " 100.0 
(control) 
9 Substrate 1 " 100.0 
(control) 
10 Substrate 1 " 99.5 
(control) 
11 Substrate 2 " 100.0 
(with plating) 
12 Substrate 2 " 100.0 
(with plating) 
13 Substrate 2 " 100.0 
(with plating) 
14 Substrate 2 " 100.0 
(with plating) 
15 Substrate 2 " 100.0 
(with plating) 
16 Substrate 2 " 100.0 
(with plating) 
17 Substrate 2 " 100.0 
(with plating) 
18 Substrate 2 " 100.0 
(with plating) 
19 Substrate 2 " 100.0 
(with plating) 
20 Substrate 2 " 100.0 
(with plating) 
______________________________________ 
TEST 6 
A TAB tape which is the same as that TEST 5 is used. After a substrate made 
of stainless steel having a thickness of 0.1 mm is formed with 
through-holes each having a diameter of 60 .mu.m by the electric 
discharging machining process, the substrate is plated with nickel so that 
the diameter of each through-hole is reduced to 50 .mu.m. Small gold balls 
each having a diameter of 60 .mu.m are arranged on the substrate. Primary 
bonding of the balls to the leads of 10 frames of the TAB tape is 
conducted. The bonding rate of the primary bonding is 100% in all the 
substrates. 
Then, secondary bonding for bonding bump-bonded TAB tape leads to IC chip 
electrodes is carried out in ten samples using ten frames of the TAB tape 
to which bumps each having a diameter of 10 .mu.m have been bonded and 10 
samples using ten frames of the TAB tape, as listed in Nos. 11 to 20 in 
TEST 5, to which bumps each having a diameter of 80 .mu.m have been 
bonded. 
In several cases of the TAB tape using the bumps each having a diameter of 
80 .mu.m, short-circuiting between adjacent leads occurs due to 
deformation of the bumps on bonding while no short-circuiting occurs in 
the TAB tape to which bumps each having a diameter of 60 .mu.m are bonded. 
This shows that use of the bumps which are relatively smaller in diameter 
gives less possibility of short-circuiting between adjacent leads so that 
a stable TAB packaging can be achieved even if the IC chip is not a 
high-density-packaged chip having a specially narrow lead pitch. 
It is confirmed that the substrate of the present embodiment is effective 
to provide an arranging substrate with small through-holes which can be 
used for arranging smaller bumps. 
TEST 7 
An arranging substrate made of a conductive ceramics having a thickness of 
0.3 mm is used to bond gold bumps to the leads of the TAB tape used for 
packaging an IC chip having total 328 electrodes at 102 .mu.m pitch along 
the peripheral four sides. The arranging substrate is formed with stepped 
through-holes in alignment with the electrodes arranged in pattern. That 
is, first, provisional holes each having a diameter of 100 .mu.m are 
formed to a depth of about 250 .mu.m in a rear side of the substrate by 
the precise electric discharging machining and then through-holes each 
having a diameter of 40 .mu.m are formed by laser machining at the 
positions of the provisional holes. In this case, the provisional holes 
each having 100 .mu.m diameter are not isolated from each other since 
adjacent holes are overlapped with each other around the periphery 
thereof. However, the through-holes having 40 .mu.m diameter are formed on 
the front side of the substrate. The two-step method of forming 
through-holes is advantageous when it is necessary to use a thicker 
substrate to assure a strength of the substrate but it is very difficult 
to directly form through-holes having 40 .mu.m diameter in a thicker 
substrate having a thickness of 0.3 mm, for example. 
The diameter of holes measured at the front side of the substrate is 
reduced to 35 .mu.m by plating the resultant substrate with nickel. Since 
the substrate of electrically conductive ceramics has a tendency that the 
surface becomes rough by laser machining in comparison with the substrate 
of stainless steel used in TEST 6, it is useful in that the plating 
provides an effect for reducing the hole diameter as well as an effect for 
smoothing the surface around the holes thereby making the separation of 
bumps easier. 
A primary bonding test is performed for ten samples each using the 
substrate made in the above manner. In each sample, the bumps of small 
gold balls each having a diameter of 45 .mu.m are arranged at positions of 
through-holes each having a diameter of 35 .mu.m formed in the substrate 
made in the above manner by reducing the pressure in the rear side of the 
substrate. Then the bumps thus arranged in ten samples are bonded to the 
leads of ten frames of TAB tape, respectively, by using bonding tool under 
a condition that the tool temperature is 520.degree. C. and the applied 
pressure is 20 gf/lead. The primary bonding rate is 100% for the 10 
samples. Further, the secondary test is carried out for the ten samples as 
above-mentioned. In each sample, the leads of the bump-bonded TAB tape 
thus made are bonded to electrodes of IC chip by using bonding machine 
under a condition that the tool temperature is 540.degree. C. and the 
applied pressure is 60 gf/lead. In the secondary test, the secondary 
bonding rate is 100% with no short-circuiting between adjacent leads. 
TEST 8 
An arranging substrate made of stainless steel having a thickness of 0.1 mm 
is used to bond gold bumps to the leads of the TAB tape used for packaging 
an IC chip having total 328 electrodes at 102 .mu.m pitch along the 
peripheral four sides, which is similar to that of TEST 7. The arranging 
substrate is formed with stepped through-holes which are inverse to those 
of TEST 3 in alignment with the arrangement pattern of the electrodes. 
That is, first, provisional holes each having a diameter of 50 .mu.m are 
formed in the front side of the substrate to a depth of 30 .mu.m by 
precise electric discharging machining and the through-holes of 40 .mu.m 
diameter are formed at the positions of the provisional holes by laser 
machining. Although it is hard to bore the 70 .mu.m thick substrate with 
through-holes of 40 .mu.m diameter, through-holes each having excellent 
roundness is obtained by rotating the substrate in a plane perpendicular 
to the direction of laser light radiation, while a focussed laser spot 
beam is repeatedly radiated. 
The substrate is coated by plating with nickel until the 40 .mu.m diameter 
of the through-holes is reduced to 35 .mu.m when measured at a depth of 30 
.mu.m from the front side of the substrate. The diameter of the 
through-holes measured at the front side of the substrate, which is 
originally 50 .mu.m, is also reduced to about 45 .mu.m. 
A primary bonding test for bonding small gold balls each having a diameter 
of 40 .mu.m arranged on the substrate made in the above manner to the 
leads of the TAB tape is conducted as follows: Small gold balls each 
having a diameter of 40 .mu.m are sucked by reducing the pressure in the 
rear side of the substrate and dropped in the holes each having a diameter 
of 45 .mu.m at the front side of the substrate. The dropped balls are held 
by stepped portions each having a diameter of 35 .mu.m, of the holes and 
provisionally secured there. If a usual flat substrate is used for 
arranging such small balls, a plurality of gold balls may be often sucked 
to one hole. Since the substrate used in the present embodiment has in the 
front side holes each having a diameter slightly larger than the diameter 
of small balls, only one small ball is allowed to fall in the hole and 
then trapped by the step-portion of the hole having 35 .mu.m diameter by a 
suction force exerted by reducing the pressure in the rear side. Even if 
another small gold ball approaches to the same hole, suction force is not 
applied to this ball. Accordingly, it is possible to prevent a plurality 
of very small gold balls from being collected in one through-hole. 
Since the diameter of each hole is 45 .mu.m at a portion from the front 
surface of the substrate to its depth of 30 .mu.m which is slightly 
smaller than the diameter of the small gold balls, the tops of the small 
balls project above the front surface of the substrate by 5 .mu.m when 
arranged thereon. Therefore, there is no difficulty in bonding the balls 
on the substrate to the leads of the TAB tape. 
It is confirmed that the substrate having stepped through-holes, of which 
the diameter is larger at its front side than its rear side, is very 
effective to treat very small bumps as mentioned-above. 
In order to manufacture a TAB tape having leads disposed at very small 
pitches and bonded with very small bumps, it is required to provide an 
arrangement of small metal balls which is used for bonding the bumps to 
the leads of the TAB tape. By the above embodiment, it is possible to 
realize a substrate adapted to be used for making such an arrangement of 
very small metal balls or spherical bumps which are hitherto very 
difficult to be practically used. As a result, it becomes possible to 
realize high density packaging which is a feature of TAB process by using 
very small spherical bumps which are excellent in bonding properties and 
eliminating a problem of very small burns on the substrate which prevents 
smooth transfer of bumps to the leads of TAB tape thereby realizing stable 
primary bonding. 
Further, in the TABs having leads at pitches which have been conventionally 
realized, it is possible to prevent short-circuiting between adjacent 
leads in the secondary bonding for connecting the leads of TAB tape to the 
electrodes of IC chip by using smaller spherical bumps for the TAB tape.