Solder ball arrangement device

A solder ball arrangement device has a thin arrangement plate having a plurality of through-holes of a truncated pyramid shape, a porous member bonded to the arrangement plate, and a housing member for receiving the arrangement plate and the porous member for defining an air space inside the housing member. A suction pump is provided to evacuate the air space and to receive an array of solder balls in the through-holes by suction. The through-holes are formed by etching, and the porous member reinforces the thin arrangement plate.

BACKGROUND OF THE INVENTION 
(a) Field of the Invention 
The present invention relates to a solder ball arrangement device and, more 
particularly, to a solder ball arrangement device for use in transferring 
an array of solder balls onto a mounting board to form an array of bump 
electrodes in a BGA (ball grid array) technique, a CSP (chip size package) 
technique, or a flip chip bonding technique. The present invention also 
relates to a method for fabrication thereof. 
(b) Description of the Related Art 
Bump electrodes formed by a BGA technique, a CSP technique, and a flip chip 
bonding technique are increasingly used in mounting a semiconductor chip 
onto a mounting board. In the recent advance of semiconductor integrated 
circuits, a large number of external pins are disposed at a smaller pitch, 
with increased mounting density, reduced device area and increased 
capacity of the integrated circuits. In the method for forming bump 
electrodes by using metallic solder balls, it is especially important to 
arrange a large number of minute metallic solder balls (hereinafter 
referred to as solder balls) efficiently at a small pitch. Some proposals 
have been made for forming the bump electrodes. 
JP-A-8(1996)-25035, for example, proposes a solder ball transfer device for 
installing an array of solder balls on a mounting board. FIG. 1A is a 
schematic cross-sectional view of the proposed solder ball transfer 
device. 
The proposed solder ball transfer device 30 comprises an alignment plate 32 
having an array of holes 32a each for receiving a solder ball 31 therein 
and an associated ejecting pin 33 disposed for each of the holes 32a for 
ejecting the solder ball 31 from the alignment plate 32. A pattern for the 
array of the holes 32a is made to be exactly equal to the pattern of 
bonding pads 35 formed on a target mounting board 34. The ejecting pin 33 
is slidably mounted by the alignment plate 32 for protruding from and 
retracting into an associated slot 32b communicated with a corresponding 
one of the holes 32a at the bottom thereof. The ejecting pin 33 is of a 
tube shape having a communicating hole 33a therein communicated with a 
suction pump not shown in the figure. 
In the conventional solder ball transfer device 30, a solder ball 31 is 
first disposed in each hole 32a, with the alignment plate 32 disposed 
upside-down. The suction pump is then operated to attract the solder ball 
31 to the tip of the ejecting pin 33 through the communication hole 33a. 
Subsequently, the alignment plate 32 is turned by a mechanism so that the 
solder balls 31 disposed on the bottom of the alignment plate 32 opposed 
to the top surface of a mounting board 34. The ejecting pins 33 are then 
ejected to thrust the solder balls 31 onto the flux 36 on the respective 
bonding pads 35, as shown in FIG. 1B, followed by release of the solder 
balls 31 from the ejecting pins 33 by stopping the suction from the 
suction pump and subsequent retraction of the ejecting pins 33. 
Thereafter, the mounting board 34 is introduced into a reflow furnace, 
wherein flux 36 is melted to fix the solder balls 31 onto the bonding pads 
35 of the mounting board 34. 
It is reported that the conventional solder ball transfer device 30 as 
described above has an advantage in that the array of the solder balls 31 
are transferred to the mounting board 34 with excellent reliability even 
if the solder ball 31 attracts electrostatic charge and/or moisture. In 
addition, the solder balls 31 are transferred to correct locations of a 
mounting board 34 even with the presence of the flux 36. 
The conventional solder ball transfer device has, however, a problem in 
that the complicated structure of the holes 32a and associated slots 32b 
in the alignment plate 32 raises the cost of the device, especially in the 
case of a high density ball pattern such as having a small pitch as low as 
300 .mu.m with a large number of pads as high as 2000. If the alignment 
plate is formed by an etching technique for achieving the high density, 
the alignment plate will suffer from lack of mechanical strength due to a 
small thickness thereof. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a solder ball 
transfer device or solder ball arrangement device which has a simple 
structure and a sufficient mechanical strength and is capable of being 
fabricated with a low cost. 
It is another object of the present invention to provide a method for 
fabricating the solder ball arrangement device as mentioned above. 
The present invention provides a solder ball arrangement device comprising 
an arrangement plate having an array of through-holes penetrating the 
arrangement plate, a porous member having first and second surfaces, the 
first surface being attached to the arrangement plate, the through-holes 
exposing portions of the first surface, and a housing member for defining 
an air space together with the second surface of the porous member, the 
housing member having a nozzle or air outlet communicated with the air 
space. 
The present invention also provides a method for manufacturing a solder 
ball arrangement device comprising the steps of forming an array of 
through-holes in a plate, bonding a first surface of the plate onto a 
porous member for exposing portions of the porous member through the 
through-holes, and receiving at least the porous member in a housing 
member having an air nozzle or air outlet to form an air space between the 
porous member and a portion of the housing member. 
In accordance with the solder ball arrangement device of the present 
invention and manufactured by the method of the present invention, a high 
density solder pattern can be formed on the arrangement plate and can be 
transferred therefrom onto a mounting board. The arrangement plate may be 
made thin enough for allow an etching process for forming the 
through-holes without suffering from lack of the strength thereof because 
the arrangement plate is supported by the porous member. 
The above and other objects, features and advantages of the present 
invention will be more apparent from the following description, referring 
to the accompanying drawings.

PREFERRED EMBODIMENTS OF THE INVENTION 
Now, the present invention is more specifically described with reference to 
accompanying drawings. Referring to FIG. 2, a solder ball arrangement 
device 11 according to a first embodiment of the present invention 
comprises an arrangement plate 13 having therein an array of through-holes 
13a having a tapered inner surface, a porous member 15 made of a porous 
material and bonded to the arrangement plate 13, and a housing member 14 
for receiving the arrangement plate 13 and the porous member 15, with an 
air space 14a left below the bottom of the porous member 15. The housing 
member 14 has a nozzle or air outlet 14b communicated with the air space 
14a. A vacuum pump not shown in the figure is connected to the nozzle 14b 
of the housing member 14 for suction of air from the air space 14a. Each 
through-hole 13a of the arrangement plate 13 can receive therein a solder 
ball 12 and has a truncated pyramid shape, the larger bottom of which is 
directed upward during arrangement of the solder balls 12 in the 
through-holes 13a. 
The arrangement plate 13 is made of silicon, for example. The porous member 
15 is made of a ceramic or a metal such as aluminum. The through-holes 13a 
are arranged corresponding to the pattern of an array of bonding pads of a 
mounting board on which the solder balls 12 are to be mounted. 
FIGS. 3A to 3B show a fabrication process of the solder ball arrangement 
device of FIG. 2. A silicon arrangement plate 13 having a thickness of 
about 300 .mu.m is first prepared. An array of holes 13a each having a 
pyramid shape are formed on the first (top) surface of the silicon 
arrangement plate 13 by an anisotropic etching technique, as shown in FIG. 
3A. The array of the holes 13a corresponds to a pattern of bonding pads on 
which solder balls are to be mounted. The silicon arrangement plate 13 is 
then ground at the second (bottom) surface of the silicon arrangement 
plate 13 opposed to the first surface by using a chemical-mechanical 
polishing technique or grinding technique, thereby forming through-holes 
13a each having a truncated pyramid shape, as shown in FIG. 3B. The 
anisotropic etching technique can provide a pattern of a larger number of 
truncated pyramid holes 13a with a smaller pitch and at a lower cost 
without suffering from lack of mechanical strength, compared to the 
conventional technique. An isotropic etching technique may be also used 
instead of the anisotropic etching technique. In this case, an array of 
truncated conical holes can be formed. 
The silicon arrangement plate 13 is then coated with an adhesive and bonded 
to a porous member 15 made of a ceramic, with the top of the truncated 
pyramid hole 13a are directed to the is porous member 15, and with the 
bottom of the truncated pyramid hole 13a being open. That is, the hole has 
a profile in a cross-section in a vertical plane which is smaller toward 
the porous member 15. 
The arrangement plate 13 and the porous member 15 are then received in the 
housing member 14, as shown in FIG. 2, with the top surface of the 
arrangement plate 13 being flush with the top opening of the housing 
member 14, and with the bottom surface of the porous member 15 defining 
the air space 14a within the housing member 14. 
In operation, a plurality of solder balls 12 are provided in the respective 
through-holes 13a for arrangement. During the provision of the solder 
balls 12, the housing member 14 may be subjected to oscillation to 
effectively arrange the solder balls 12 inside the truncated pyramid holes 
13a. In the present embodiment, the truncated pyramid hole 13a has the 
larger bottom opening of the pyramid exposed which effectively receives 
the solder ball 12. After the arrangement of the solder balls 12, a 
suction pump is operated to attract the solder balls 12 to the smaller 
bottom of the respective truncated pyramid holes 13a. Subsequently, the 
solder ball arrangement device 11 is turned upside-down together with the 
solder balls 12 so that the array of the solder balls 12 are opposed to an 
array of bonding pads on a mounting board. The solder ball arrangement 
device 11 is then thrust against the mounting board to press the array of 
solder balls 12 onto the respective bonding pads, followed by stoping 
operation of the suction pump, thereby transferring the solder balls onto 
the mounting board. During the transfer of the solder balls, the solder 
ball arrangement device is heated up to a melting point of the solder 
balls. 
The solder ball arrangement device according to the present embodiment has 
a simple structure, and accordingly, can be manufactured at a lower cost. 
In addition, since the silicon arrangement plate 13 having a small 
thickness is bonded onto a porous member 15 having a larger thickness, 
e.g., 5 mm, the mechanical strength of the solder ball arrangement device 
is improved. 
Referring to FIG. 4, a solder ball arrangement device 21 according to a 
second embodiment of the present invention comprises an arrangement plate 
23 having a plurality of truncated pyramid holes 23a for arranging solder 
balls 12, and a porous member 25 bonded thereto, and a housing member 24, 
which are similar to those in the first embodiment. 
The arrangement plate 23 has an array of truncated pyramid holes 23a, the 
larger bottom surface of which opposes to the porous member 25. The top of 
the truncated pyramid hole 23a has a size smaller than the diameter of the 
solder balls 12. The solder balls 12 are attracted to the top of the 
truncated pyramid holes 23a. In this configuration, the attracting force 
by the vacuum is larger than that in the first embodiment. In addition, it 
is possible to prevent two or more solder balls 12 from attaching to one 
of the pyramid holes 23a. 
FIGS. 5A to 5C show a fabrication process of the solder ball arrangement 
device of the present embodiment. A silicon plate 23 having a thickness of 
300 .mu.m is first prepared. An array of holes 23a each having a pyramid 
shape is formed on the first (top) surface of the silicon plate 23 by an 
anisotropic etching technique, as shown in FIG. 5A. The array of the 
pyramid holes 23a correspond to a pattern of bonding pads on which solder 
balls are to be mounted. The anisotropic etching technique provides a 
pattern of a larger number of holes with a smaller pitch and at a lower 
cost, compared to the conventional technique. An isotropic etching 
technique may be used instead of the anisotropic etching technique to 
provide conical holes. 
The silicon plate 23 is then coated with an adhesive and bonded to a porous 
member 25 made of a ceramic, with the larger bottoms of the pyramid holes 
23a are directed to the porous member 15. The silicon plate 23 is then 
ground at the second (top) surface of the silicon plate 23 opposed to the 
first surface by using a chemical-mechanical polishing technique or 
grinding technique, thereby forming truncated pyramid holes 23a each 
penetrating the arrangement plate 23, as shown in FIG. 5C. In this 
embodiment, the grinding of the arrangement plate 23 after bonding the 
same to the porous member 25 having a thickness of 5 mm, for example, 
results in less failure because of the reinforced mechanical strength of 
the arrangement plate 23. The arrangement plate 23 and the porous member 
25 are then received in a housing, similar to the first embodiment, to 
complete the solder ball arrangement device of the second embodiment. 
Since the above embodiments are described only as examples, the present 
invention is not limited to the above embodiments and various 
modifications or alterations can be easily made therefrom by those skilled 
in the art without departing from the scope of the present invention. For 
example, the materials or the shapes of the arrangement plate or porous 
member are not limited to the above embodiments.