U.S. patent application number 11/066153 was filed with the patent office on 2005-06-30 for method of mounting electronic component on substrate without generation of voids in bonding material.
This patent application is currently assigned to FUJITSU LIMITED. Invention is credited to Suehiro, Mitsuo, Yamada, Hiroshi, Yamamoto, Tsuyoshi.
Application Number | 20050139389 11/066153 |
Document ID | / |
Family ID | 19108132 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050139389 |
Kind Code |
A1 |
Yamamoto, Tsuyoshi ; et
al. |
June 30, 2005 |
Method of mounting electronic component on substrate without
generation of voids in bonding material
Abstract
When an electronic component is mounted on a substrate, the
electronic component is first placed on the substrate with a solid
support interposed between the electronic component and the
substrate. The solid support serves to space a terminal conductor
of the electronic component from a corresponding terminal pad on
the substrate. A conductive bonding material is then melted on the
terminal pad. The melted conductive bonding material gets exposed
to the peripheral atmosphere over a larger area. Even if a bubble
is generated within the melted conductive bonding material, the
bubble is allowed to easily get out of the melted conductive
bonding material. Removal of the gas is promoted in the melted
conductive bonding material. The solid support is subsequently
melted. The electronic component is moved down toward the
substrate, thereby contacting the terminal conductor with the
melted conductive bonding material on the corresponding terminal
pad. Removal of the gas in this manner leads to improvement in the
strength of bonding between the substrate and the electronic
component.
Inventors: |
Yamamoto, Tsuyoshi;
(Kawasaki, JP) ; Suehiro, Mitsuo; (Kawasaki,
JP) ; Yamada, Hiroshi; (Kawasaki, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW
SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
FUJITSU LIMITED
Kawasaki
JP
|
Family ID: |
19108132 |
Appl. No.: |
11/066153 |
Filed: |
February 28, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11066153 |
Feb 28, 2005 |
|
|
|
10073106 |
Feb 12, 2002 |
|
|
|
Current U.S.
Class: |
174/260 ;
174/258 |
Current CPC
Class: |
H05K 3/3494 20130101;
H05K 2203/0475 20130101; H01L 2224/73204 20130101; H01L 2224/73103
20130101; Y10T 29/49146 20150115; H05K 2201/0129 20130101; Y10T
29/4913 20150115; Y02P 70/50 20151101; H05K 2201/10734 20130101;
H01L 2224/29035 20130101; H05K 3/3436 20130101; Y10T 29/49144
20150115; Y10T 29/49169 20150115; H05K 2203/0182 20130101; H05K
2203/1105 20130101; Y10T 29/49151 20150115; Y10T 29/49155 20150115;
H01L 2224/29036 20130101; H05K 3/305 20130101; H05K 2201/10977
20130101; Y10T 29/49163 20150115; H01L 2224/73103 20130101; H01L
2924/00012 20130101 |
Class at
Publication: |
174/260 ;
174/258 |
International
Class: |
H05K 001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 19, 2001 |
JP |
2001-284886 |
Claims
1-13. (canceled)
14. An electronic circuit board comprising: a substrate; an
electronic component mounted on a surface of the substrate and
having a terminal conductor received on a terminal pad on the
substrate; and a thermoplastic resin material interposed between
the substrate and the electronic component.
15. The electronic circuit board according to claim 14, wherein
said thermoplastic resin material has a higher heat
conductivity.
16. An electronic component unit comprising: a terminal conductor
of a predetermined height standing on a surface opposed to a
substrate; and a solid support standing on the surface, said solid
support having a height larger than the predetermined height.
17. The electronic component unit according to claim 16, wherein
said solid support is made of a thermoplastic resin material.
18. The electronic component unit according to claim 16, wherein
said solid support has an adherent property on its surface.
19. The electronic component unit according to claim 16, wherein
said thermoplastic resin material has a higher heat conductivity.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of mounting an
electronic component, such as a ball grid array (BGA) semiconductor
package. In particular, the invention relates to a method of
mounting an electronic component on a substrate by melting a
conductive bonding material on a terminal pad on the substrate.
[0003] 2. Description of the Prior Art
[0004] Some methods of mounting an electronic component on a
substrate utilize a solder paste. The solder paste is previously
printed on terminal pads disposed on the surface of the substrate.
Terminal conductors, such as solder balls, of the electronic
component are placed on the corresponding terminal pads. After the
electronic component has been set on the substrate in this manner,
the substrate is passed through a reflow oven. Solder particles
dispersed within the solder paste are caused to melt in the reflow
oven. Subsequent cooling treatment serves to solidify the solder on
the terminal pads on the substrate. The terminal conductors of the
electronic component are thus bonded to the corresponding terminal
pads on the substrate.
[0005] The solder paste usually includes an organic solvent. When
the solder particles melt in the solder paste, the organic solvent
is forced to vaporize in the melting solder. In this case, the
vaporized or gaseous organic solvent is locked within the melting
solder in the aforementioned conventional method, since the surface
of the solder paste is covered with the terminal conductors of the
electronic component. Voids remain within the solidified solder.
The voids may cause a failure in electric contact between the
electronic component and the substrate. The voids are supposed to
reduce the strength of bonding between the electronic component and
the substrate.
SUMMARY OF THE INVENTION
[0006] It is accordingly an object of the present invention to
provide a method of mounting an electronic component on a
substrate, which is capable of enhancing the reliability of bonding
between the electronic component and the substrate.
[0007] According to a first aspect of the present invention, there
is provided a method of mounting an electronic component on a
substrate, comprising: placing the electronic component on the
substrate with a solid support interposed between the electronic
component and the substrate so as to space a terminal conductor of
the electronic component from a corresponding terminal pad on the
substrate; melting a conductive bonding material on the terminal
pad; and thereafter melting the solid support so as to move down
the electronic component toward the substrate, thereby contacting
the terminal conductor with the conductive bonding material melting
on the corresponding terminal pad.
[0008] The method enables a reliable prevention of contact between
the conductive bonding material on the terminal pad and the
terminal conductor when the conductive bonding material gets
melted. The melted conductive bonding material gets exposed to the
peripheral atmosphere over a larger area. Even if a bubble is
generated within the melted conductive bonding material, the bubble
is allowed to easily get out of the melted conductive bonding
material. Removal of the gas is promoted in the melted conductive
bonding material. Removal of the gas in this manner leads to
improvement in the strength of bonding between the substrate and
the electronic component. A solder paste may be supplied to the
surface of the terminal pad in this method. The solder paste may
comprise a flux including an organic solvent, for example, and
solder particles as the conductive bonding materials dispersed in
the flux. When the solder particles get melted, the organic solvent
in the solder paste may get vaporized in the melted solder.
[0009] In this case, a solid support is employed to lift the
electronic component above the substrate. The solid support of this
type can simply be interposed between the substrate and the
electronic component. The terminal conductor of the electronic
component can easily be prevented from contacting the terminal pad
on the substrate. Moreover, the terminal conductor is caused to
fall or drop toward the terminal pad in response to melting of the
solid support. Contact can be established between the terminal
conductor and the terminal pad with a simple structure. The solid
support may be made of a thermoplastic resin material having the
melting point higher than that of the conductive bonding material.
The solid support of this type provides an electronic circuit board
comprising: a substrate; an electronic component mounted on a
surface of the substrate and having a terminal conductor received
on a terminal pad on the substrate; and a thermoplastic resin
material interposed between the substrate and the electronic
component.
[0010] According to a second aspect of the present invention, there
is provided a method of mounting an electronic component on a
substrate, comprising: melting a conductive bonding material on a
terminal pad on the substrate under a high temperature atmosphere;
and contacting a terminal conductor of the electronic component on
the conductive bonding material on the terminal pad continuously
under the high temperature atmosphere.
[0011] The conductive bonding material is allowed to get exposed to
the peripheral atmosphere over a larger area. Even if a bubble is
generated within the melted conductive bonding material, the bubble
easily gets out of the melted conductive bonding material. The gas
is reliably removed from the melted conductive bonding material.
The terminal conductor of the electronic component can be placed on
the terminal pad on the substrate after removal of the gas out of
the melted conductive bonding material. Removal of the gas in this
manner leads to improvement in the strength of bonding between the
substrate and the electronic component. A solder paste may be
supplied to the surface of the terminal pad in this method. The
solder paste may comprise a flux including an organic solvent, for
example, and solder particles as the conductive bonding materials
dispersed in the flux. When the solder particles get melted, the
organic solvent in the solder paste may get vaporized in the melted
solder.
[0012] Moreover, the conductive bonding material is simply exposed
under the high temperature atmosphere when the conductive bonding
material is to be melted. Groups of the electronic components can
simultaneously be mounted on one or more substrates. The
productivity can be improved as compared with the case where the
electronic components are separately or individually mounted on the
substrate, or the mounting of the electronic components is
separately or individually effected on the individual
substrates.
[0013] The method may further comprise: placing the electronic
component on the substrate, prior to melting of the conductive
bonding material, with a solid support interposed between the
electronic component and the substrate so as to space the terminal
conductor from the terminal pad; and melting the solid support so
as to move down the electronic component toward the substrate,
thereby contacting the terminal conductor with the conductive
bonding material on the corresponding terminal pad, when the
terminal conductor is contacted on the terminal pad. In this case,
the solid support may be made of a thermoplastic resin material
having the melting point higher than that of the conductive bonding
material.
[0014] According to a third aspect of the present invention, there
is provided a method of mounting an electronic component on a
substrate, comprising: melting a solder paste on a terminal pad on
the substrate; and placing a terminal conductor of the electronic
component on the solder paste on the terminal pad, said solder
paste being kept melted.
[0015] The solder particles in the solder paste get melted in the
melted solder paste. The solvent in the solder paste simultaneously
gets vaporized. Since the terminal conductor of the electronic
component is prevented from contacting the terminal pad on the
substrate, the melted solder is allowed to get exposed to the
peripheral atmosphere over a larger area. The gaseous or vaporized
organic solvent easily gets out of the melted solder. The terminal
conductor of the electronic component can be placed on the terminal
pad on the substrate after removal of the gas out of the melted
conductive bonding material. Generation of voids can be prevented
in the solidified solder. Removal of the gas or the voids in this
manner leads to improvement in the strength of bonding between the
substrate and the electronic component.
[0016] The method may further comprise in the aforementioned
manner: setting the electronic component on the substrate, prior to
melting of the solder paste, with a solid support interposed
between the electronic component and the substrate so as to space
the terminal conductor from the terminal pad; and melting the solid
support so as to move down the electronic component toward the
substrate, thereby contacting the terminal conductor with the
solder paste on the corresponding terminal pad, said solder paste
being kept melted. In this case, the solid support may be made of a
thermoplastic resin material having a melting point higher than
that of the solder paste. The method likewise serves to provide an
electronic circuit board comprising: a substrate; an electronic
component mounted on a surface of the substrate and having a
terminal conductor received on a terminal pad on the substrate; and
a thermoplastic resin material interposed between the substrate and
the electronic component.
[0017] In any event, the solid support may have an adherent
property on its surface. The adherent property of the solid support
may be utilized to stick the electronic component on the substrate.
The electronic component can thus stably be positioned on the
substrate even during transportation or displacement. The adherent
property may be established based on the natural property of the
material for the solid support or based on an adhesive provided on
the surface of the solid support.
[0018] The solid support also may have a high heat conductivity.
The solid support of this type leads to a promoted radiation of
heat from the electronic component mounted on the substrate. The
solid support may contain alumina (Al.sub.2O.sub.3) particles
dispersed in a resin material.
[0019] In any of the aforementioned methods, there may be provided
an electronic component unit comprising: a terminal conductor of a
predetermined height standing on a surface opposed to a substrate;
and a solid support standing on the surface, said solid support
having a height larger than the predetermined height.
[0020] When the electronic component unit is set on the substrate,
the solid support is naturally interposed between the electronic
component and the substrate. The operator is not required to
additionally insert the solid support before or after setting the
electronic component on the substrate. The productivity can thus be
improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The above and other objects, features and advantages of the
present invention will become apparent from the following
description of the preferred embodiment in con junction with the
accompanying drawings, wherein:
[0022] FIG. 1 is a perspective view illustrating an electronic
circuit board;
[0023] FIG. 2 is an enlarged vertical sectional view of the
electronic circuit board for illustrating the structure of a ball
grid array (BGA) semiconductor package in detail;
[0024] FIG. 3 is a plan view of the BGA semiconductor package for
illustrating the array of solder balls;
[0025] FIG. 4 is an enlarged partial section view of a printed
wiring board for illustrating the process of placing the BGA
semiconductor package on the printed wiring board;
[0026] FIG. 5 is an enlarged partial section view of the printed
wiring board for illustrating the process of generating melted
solder on terminal pads on the printed wiring board;
[0027] FIG. 6 is an enlarged partial section view of the printed
wiring board for illustrating the process of melting a solid
support between the printed wiring board and the BGA semiconductor
package;
[0028] FIG. 7 is a perspective view schematically illustrating the
structure of an electronic component unit;
[0029] FIG. 8 is an enlarged partial section view of a printed
wiring board for illustrating the process of placing a full matrix
BGA semiconductor package on the printed wiring board; and
[0030] FIG. 9 is an enlarged partial section view of a printed
wiring board for illustrating the process of placing a quad flat
package (QFP) on the printed wiring board.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0031] FIG. 1 schematically illustrates the structure of a
electronic circuit board 11. The electronic circuit board 11
includes a printed wiring board or substrate 12 of a resin
material, for example, and one or more electronic components 13,
such as ball grid array (BGA) semiconductor packages, mounted on
the surface of the printed wiring board 12. An electrically
conductive wiring pattern, not shown, spreads over the surface
or/and interior of the printed wiring board 12 so as to establish
electric connections between the BGA semiconductor packages 13, for
example.
[0032] As shown in FIG. 2, the BGA semiconductor package 13
includes a semiconductor chip 15 mounted on the upper surface of a
small-sized printed wiring board or substrate 14 of a ceramic
material, for example. A plurality of connection terminals 16 are
attached to the lower surface of the small-sized printed wiring
board 14. The connection terminals 16 are received on corresponding
terminal pads 17 on the printed wiring board 12. In this manner,
electric connection can be established between terminal pads, not
shown, of the small-sized printed wiring board 14 and the terminal
pads 17 on the printed wiring board 12.
[0033] A so-called underfill 18 is interposed between the
small-sized printed wiring board 14 of the BGA semiconductor
package 13 and the printed wiring board 12. The underfill 18 may be
made of a thermoplastic resin material, for example. The connection
terminals 16 are embedded within the underfill 18. The underfill 18
serves to reinforce the strength of bonding between the BGA
semiconductor package 13 and the printed wiring board 12. In
addition, the underfill 18 reliably prevents the individual
connection terminals 16 from getting exposed to the atmosphere, for
example, so that corrosion or deterioration can be prevented in the
connection terminals 16.
[0034] Next, a detailed description will be made on a method of
producing the electronic circuit board 11. The electronic
components, namely, the BGA semiconductor packages 13 are first
prepared. As shown in FIG. 3, a plurality of bumps or solder balls
19 of a predetermined array are attached on the back surface of the
small-sized printed wiring board 14. It should be noted that a
naked space 21 without any solder balls 19 is defined at a central
area of the back surface of the small-sized printed wiring board
14. The back surface of the small-sized printed wiring board 14 is
allowed to fully get exposed at the naked space 21 in the BGA
semiconductor package 13.
[0035] As shown in FIG. 4, the BGA semiconductor package 13 is
placed on the upper surface of the printed wiring board 12. The
terminal pads 17 are formed on the upper surface of the printed
wiring board 12. The terminal pads 17 are arranged in the
corresponding array for the individual BGA semiconductor packages
13. A solder paste 22 is previously printed over the individual
terminal pads 17. The solder paste 22 consists of a flux including
an organic solvent, and a conductive bonding material, namely,
solder particles dispersed in the flux.
[0036] A solid support 23 is interposed between the printed wiring
board 12 and the BGA semiconductor package 13. The BGA
semiconductor package 13 is received on the top surface of the
solid support 23 at the naked space 21 of the small-sized printed
wiring board 14. The solid support 23 serves to lift the BGA
semiconductor package 13 above the surface of the printed wiring
board 12. Specifically, the solid support 23 serves to space the
solder balls 19 of the BGA semiconductor package 13 from the
surface of the terminal pads 17. The individual solder balls 19 are
prevented from contacting the solder paste 22 on the corresponding
terminal pads 17.
[0037] Here, the melting point of the solid support 23 is set
higher than that of the solder paste 22 or the solder particles. If
the solder particles are made of an eutectic solder having the
melting point of 183 degrees Celsius, for example, the solid
support 23 may be made of a material having the melting point of
approximately 200 degrees Celsius. The solid support 23 may be made
of a thermoplastic resin material such as a polyurethane-based
resin, a polyester-based resin, an acrylic-based resin, rosin, a
polyamide-based resin, or the like. Alternatively, the solid
support 23 may be made of a material other than the aforementioned
resin material.
[0038] The solid support 23 preferably has an adherent property on
its surface, for example. The adherent property of the solid
support 23 may be utilized to stick the BGA semiconductor package
13 on the printed wiring board 12. The BGA semiconductor package 13
can thus stably be positioned on the printed wiring board 12 even
during transportation or displacement. The adherent property may be
established based on the natural property of the material for the
solid support 23 or based on an adhesive provided on the surface of
the solid support 23.
[0039] Thereafter, a relowing process is effected. The printed
wiring board 12 is inserted into a reflow oven. A high temperature
atmosphere of 220 degrees Celsius is maintained in the reflow oven.
As shown in FIG. 5, the solder particles in the solder paste 22 are
first allowed to melt on the surface of the terminal pads 17. The
organic solvent simultaneously gets vaporized. The melted solder 24
remains on the surface of the terminal pads 17. The solder balls 19
of the BGA semiconductor package 13 also gets melted. The
individual solder ball 19 maintains its spherical shape based on
the surface tension.
[0040] In this situation, the temperature of the solid support 23
does not yet reach the melting point. Specifically, the solid
support 23 keeps the solder balls 19 of the BGA semiconductor
package 13 spaced from the melted solder 24 on the terminal pads 17
by a predetermined space w. The surface of the melted solder 24
gets exposed to the peripheral atmosphere. The vaporized or gaseous
organic solvent in the solder paste 22 is allowed to easily get out
of the melted solder 24. Removal of the gas can be promoted in the
melted solder 24.
[0041] When the printed wiring board 12 is further maintained in
the reflow oven, the temperature of the solid support 23 reaches
the melting temperature. The solid support 23 gets melted.
Specifically, the solid support 23 gets fluidized. The solid
support 23 is thus removed below the BGA semiconductor package 13.
The BGA semiconductor package 13 is allowed to drop toward the
printed wiring board 12 based on its own weight. As shown in FIG.
6, the solder balls 19 are thus received on the corresponding
terminal pads 17. The solder ball 19 gets unified with the melted
solder 24 on the terminal pad 17. In this manner, the connection
terminals 16 of the melted state can be established. When the
gravity acting from the small-sized printed wiring board 14 to the
connection terminals 16 is balanced with the overall surface
tension of the connection terminals 16, the small-sized printed
wiring board 14 stops falling or dropping.
[0042] The fluid of the solid support 23 spreads over the surface
to the printed wiring board 12 between the connection terminals 16.
The fluid fills the space defined between the printed wiring board
12 and the small-sized printed wiring board 14. The fluid remain
within the space between the printed wiring board 12 and the
small-sized printed wiring board 14 based on its own surface
tension.
[0043] Thereafter, the printed wiring board 12 is taken out of the
reflow oven. The printed wiring board 12 is subjected to a cooling
treatment in the normal atmosphere or at a room temperature. The
fluid gets solidified so as to provide the underfill 18 between the
printed wiring board 12 and the small-sized printed wiring board
14. The connection terminals 16 subsequently get solidified.
Electric connection can thus be obtained between the printed wiring
board 12 and the small-sized printed wiring board 14. The mounting
of the BGA semiconductor package 13 has been completed.
[0044] In particular, in the case where the BGA semiconductor
packages 13 are to be mounted on the single printed wiring board
12, the printed wiring board 12 needs be exposed only once to the
high temperature atmosphere in the aforementioned method. The BGA
semiconductor packages 13 are simultaneously mounted on the printed
wiring board 12. The productivity can be improved as compared with
the case where the BGA semiconductor packages 13 are separately or
individually mounted on the printed wiring board 12. The production
time is also shortened. Moreover, a group of the printed wiring
boards 12 may simultaneously be subjected to the high temperature
atmosphere in the aforementioned method. The productivity can be
improved as compared with the case where the mounting of the BGA
semiconductor packages 13 is separately or individually effected on
the individual printed wiring boards 12. The production time is
still further shortened.
[0045] As shown in FIG. 7, when the aforementioned method is to be
realized, an electronic component unit 26 may be prepared. The
electronic component unit 26 includes the BGA semiconductor package
13 and the solid support 23. The solid support 23 is previously
attached to the small-sized printed wiring board 14 at the naked
space 21. In this case, the solid support 23 should have the height
H larger than the height h of the terminal conductors or solder
balls 19 on the back surface of the small-sized printed wiring
board 14. When the electronic component unit 26 of this type is
placed on the printed wiring board 12, the solid support 23 can be
interposed between the printed wiring board 12 and the small-sized
printed wiring board 14 so as to space the solder balls 19 of the
BGA semiconductor package 13 from the corresponding terminal pads
17 on the printed wiring board 12, as is apparent from reference to
FIG. 4, for example.
[0046] The volume of the solid support 23 may be determined as
follows:
[0047] [Expression 1]
As.multidot.H.gtoreq.=Ac.multidot.g-Vt.multidot.n (1)
[0048] Here, the constant As represents the area of the bottom of
the solid support 23. The constant Ac represents the area of the
back surface of the small-sized printed wiring board 14. The
constant g represents the space between the front surface of the
printed wiring board 12 and the back surface of the small-sized
printed wiring board 14 in the final electronic circuit board 11.
The constant Vt represents the volume of the single solder ball 19.
The constant n represents the number of the solder balls 19
interposed between the printed wiring board 12 and the small-sized
printed wiring board 14. The space g may be set at approximately
60% of the height h of the solder balls 19, for example. The
setting in this manner enables establishment of the underfill 18
based on the solid support 23 without any supplement of materials.
It should be noted that the volume of the solid support 23 may be
set smaller than the volume of the underfill 18.
[0049] In addition, the height H of the solid support 23 should be
set as follows:
[0050] [Expression 2]
H>h+t+p (2)
[0051] Here, the constant t represents the height of the solder
paste on the surface of the terminal pad 17. The constant p
represents the thickness of the terminal pad 17 superposed on the
surface of the printed wiring board 12. The height t of the solder
paste 22 may be determined as follows:
[0052] [Expression 3] 1 t = 3 Vm + ( 3 Vm ) 2 + r 6 3 + 3 Vm - ( 3
Vm ) 2 + r 6 3 ( 3 )
[0053] Here, the constant Vm represents the volume of the melted
solder 24 existing on the terminal pad 17. The constant r
represents the radius of the terminal pad 17. The volume Vm of the
melted solder 24 may be determined as follows:
[0054] [Expression 4]
Vm=Vp.multidot.m (4)
[0055] Here, the constant Vp represents the volume of the solder
paste 22 when printed. The constant m represents the content of the
solder particles in the solder paste in the form of ratio in
volume. The content m may be set at approximately 0.5, for example.
The volume Vp of the solder paste 22 may be determined as
follows:
[0056] [Expression 5] 2 Vp = D 2 4 tm k ( 5 )
[0057] Here, the constant tm represents the thickness of a mask
employed to print the solder paste 22. The constant D represents
the diameter of the opening defined in the mask at a position
corresponding to the terminal pad 17. The constant k represents the
rate or percentage of filling of the solder paste 22 within the
opening. The rate k of filling may be set approximately in a range
between 60% and 80%, for example. In general, the height t of the
solder paste 22 gets smaller than the thickness m of the mask. It
should be noted that the height t of the solder paste 22 may be
replaced with the thickness tm of the mask in the aforementioned
[Expression 2].
[0058] The aforementioned method may be employed to mount a BGA
semiconductor package 13a of a full matrix type. The solder balls
19 of the full matrix are arranged on the back surface of the
small-sized printed wiring board in the full matrix BGA
semiconductor package 13a. In order to realize the mounting of the
full matrix BGA semiconductor package 13a on the printed wiring
board 12, the solid support 23 may be provided in the form of a
stud, as shown in FIG. 8, for example. The solid support 23 may be
located on the individual corners of the small-sized printed wiring
board 14.
[0059] The solder particles in the solder paste 22 is allowed to
melt on the terminal pads 17 prior to melting of the solid supports
23. The organic solvent simultaneously gets vaporized. The melted
solder is allowed to get exposed to the peripheral atmosphere over
a larger area. Accordingly, the vaporized or gaseous organic
solvent in the solder paste 22 is allowed to easily get out of the
melted solder. Removal of the gas can be promoted in the melted
solder. After solidification of the connection terminals 16, a
thermosetting resin material underfill may be injected within the
space between the printed wiring board 12 and the small-sized
printed wiring board 14.
[0060] Otherwise, the aforementioned method may be employed to
mount a quad flat package (QFP) 13b. As shown in FIG. 9, the
terminal conductors or terminal leads 28 extend outward from the
side surfaces of a package body 27 in the QFP 13b. The individual
terminal leads 28 are received on the corresponding terminal pads
17 on the printed wiring board 12. As is apparent from FIG. 9, the
solid support 23 may be employed to mount the QFP 13b on the
printed wiring board 12 in the aforementioned manner. The solid
support 23 may be located at the central area of the package body
27.
[0061] The solder particles in the solder paste 22 is allowed to
melt on the terminal pads 17 prior to melting of the solid support
23. The organic solvent simultaneously gets vaporized. The melted
solder is allowed to get exposed to the peripheral atmosphere over
a larger area. Accordingly, the vaporized or gaseous organic
solvent in the solder paste 22 is allowed to easily get out of the
melted solder. Removal of the gas can be promoted in the melted
solder.
[0062] The solid support 23 may be made of a thermoplastic resin
material having a high heat conductivity. The thermoplastic resin
of this type may comprise alumina (Al.sub.2O.sub.3) particles
dispersed in a resin material. Employment of the thermoplastic
resin material having a high heat conductivity leads to a promoted
radiation of heat from the BGA semiconductor package 13, the full
matrix BGA semiconductor package 13a, and the QFP 13b. As long as
the solid support 23 after melting and solidification is prevented
from contacting the connection terminals 16 and the terminal leads
28, the solid support 23 may have a property of electrically
conductivity.
[0063] It should be noted that any types of terminal conductors,
other than the aforementioned solder balls 19, may be employed in
the BGA semiconductor package 13 and the full matrix BGA
semiconductor package 13a.
* * * * *