Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1998-07-21
2004-05-04
Talbott, David L. (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S261000
Reexamination Certificate
active
06730858
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a circuit board comprising a conductive pattern section with a pattern formed on a conductive layer on a substrate and in particular to a circuit board in which bonding areas are defined in a conductive pattern section and an ultrasonic bonding method is used to join bumps of a part mounted on the board.
A circuit board comprising a conductive layer such as copper foil bonded to a substrate and formed in a desired pattern for realizing wiring connection is used as a card-type printed-circuit board used with a large electronic machine. In addition, in recent years, various circuit boards, large and small, have been used diversely as high-density packaging methods of multi-chip mounting, bear chip mounting, etc., have become pervasive. Examples of the circuit boards are a circuit board to which a chip part is directly bonded with face down, a circuit board to which bumps and tabs can be bonded ultrasonically, and a circuit board serving as both a wiring board and a vessel of parts for use with electronic parts.
A circuit board for use with a chip-type surface acoustic wave device will be discussed with reference to FIG.
11
and
FIG. 12
as a recent circuit board example dealing with high-density packaging of the prior art.
FIG. 11
is an assembly view to show the structure of a conventional surface acoustic wave device. For purposes of signal input/output, ground connection, and as required, power connection, eight electrodes bumps (simply bumps)
22
each about several ten microns high are installed on one side (rear side in
FIG. 11
) of a surface acoustic wave chip
21
of a niobium acid lithium crystal, etc., which will be hereinafter called chip
21
. A circuit board
23
on which the chip
21
is placed comprises a conductive pattern section
24
with a pattern formed on a conductive layer, and bonding areas
25
are defined in the conductive pattern section
24
as predetermined areas in which the bumps
22
are bonded ultrasonically and secured fixedly. The bonding area
25
is an area comprising a bonding position that the bump
22
directly strikes and a portion where the bump is spread, welded, and joined by ultrasonic bonding. After the chip
21
is placed on the circuit board
23
by ultrasonic bonding, the circuit board
23
is housed in a vessel
26
and sealed by a lid
27
. Such a related art example can also be seen in Unexamined Japanese Patent Publication 4-65909.
The circuit board
23
generally comprises metal foil of copper, etc., about 12-75 microns thick deposited as a conductive layer via an adhesive layer about several ten microns thick on an insulating substrate of a resin, ceramics, etc., about 0.2-2.5 millimeters thick, the conductive layer being etched in a desired pattern for forming a plane circuit of the conductive pattern section
24
. In recent circuit boards, a conductive layer is etched in a width or space of about several hundred microns for forming a high-precision conductive pattern section.
Ultrasonic bonding for mounting a part with bumps on the circuit board will be discussed with reference to FIG.
12
. First, the chip
21
with the bump
22
face down is attracted at the chip of a head section
29
of a ultrasonic bonder
28
. Next, each of the bumps
22
is aligned with the center of each bonding area (bonding position) in the conductive pattern section
24
on the circuit board
23
, the head section
29
is brought down, and the bumps
22
are pressed against the surface of the conductive pattern section
24
. Ultrasound is added to the bumps
22
via the chip
21
from the head section
29
and ultrasonic energy is used to join the bumps
22
and the conductive pattern section
24
for fixedly securing the chip
21
to the circuit board
23
.
However, according to the related art, the following problems remain unsolved:
To ultrasonically bond a part provided with bumps onto a circuit board, it is difficult to provide all bumps with the same degree of bonding strength and the bonding strength varies from one bump to another.
To ultrasonically bond the bumps to the bonding areas, essentially it is desirable to apply optimum ultrasonic bonding energy to the bumps in response to the bump shape, the conductive pattern section form containing the bonding areas, and the like. For example, to ultrasonically bond the bumps to the bonding areas of comparatively narrow conductive land portions separated in three directions by the pattern boundary as shown in conductive lands
24
a
in the conductive pattern section
24
in
FIG. 11
, it is desirable to apply comparatively strong ultrasonic energy for a long time and enlarge load imposed on the chip.
To ultrasonically bond the bumps to the bonding areas of comparatively wide conductive land portions as shown in conductive lands
24
b
in the conductive pattern section
24
in
FIG. 11
, it is not necessary to apply strong ultrasonic energy to the bumps or impose large load thereon; if too strong ultrasonic energy is applied to the bumps, the circuit board or the chip is cracked and broken, etc.
However, on the one hand, usually the shape and area of the conductive pattern section formed in the circuit board vary diversely depending on the electric signal type, current capacity, pattern application, etc.; on the other hand, the ultrasonic energy applied to the chip from the head section of the ultrasonic bonder is distributed only mechanically simply among the bumps by pressing the chip against the conductive pattern section.
It is desirable to apply appropriate ultrasonic energy separately to each of the bumps combined with the bonding areas. In fact, however, joining energy cannot be adjusted. Resultantly, to ultrasonically bond a chip provided with bumps to a circuit board, the energy for joining the bumps and bonding areas becomes too much or too little; the ultrasonic bonding failure rate is high and the joint parts also lack reliability.
Further, taking a flexible manufacturing system or an automatic packaging apparatus with a robot as the recent trend as an example, to use one ultrasonic bonder to ultrasonically bond a chip with bumps to various circuit boards or various parts with bumps to points of a large circuit board in multi-chip mounting, etc., the operation conditions of the ultrasonic bonder must be again adjusted to the optimum bonding conditions each time the circuit board type changes or the conductive pattern section shape or the number of bumps of a part varies; thus there is a serious defect of lacking practicality because the substantial productivity extremely lowers.
Resultantly, to mount a chip with bumps on a circuit board, the ultrasonic bonding involves problems of lacking versatility, poor conductivity, and lacking reliability after joining.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a circuit board which enables a chip with bumps to be fixedly secured to bonding areas in a conductive pattern area on the circuit board evenly in high bonding strength.
Other and further objects and new features of the invention will become apparent from the following description of embodiments.
To the end, according to a first aspect of the invention, there is provided a circuit board comprising a conductive pattern section with a pattern formed on a conductive layer provided on a board main body, wherein two or more bonding positions that bumps of a part mounted by ultrasonic bonding strike are set in the conductive pattern section, characterized in that an isolated notch part or recess (for example, an island-like notch or recess pattern surrounded on four sides by the level difference from the conductive layer) is formed in the conductive layer in the proximity of at least one bonding position.
According to a second aspect of the invention, there is provided a circuit board comprising a conductive pattern section with a pattern formed on a conductive layer provided on a board main body, wherein two or more bonding positions that bumps of a part mounted by ultrasonic bonding strike are set
Gotoh Masashi
Honda Kenji
Kanazawa Jitsuo
Yamamoto Syuichiro
Norris Jeremy
Talbott David L.
TDK Corporation
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