Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-06-18
2001-06-12
Young, Lee (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S832000, C029S855000, C029S412000, C083S929100, C174S050510, C264S272170, C264S272110, C264S157000, C264S236000, C264S347000
Reexamination Certificate
active
06243945
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic part in which one or more semiconductor elements or the like are mounted on a substrate and sealed with the resin, and a method for manufacturing the same.
2. Description of the Related Art
A conventional electronic part and the method for manufacturing it will be explained with reference to
FIGS. 9-13
. In most commercial processes, a large number of electronic components are mounted on a relatively large mother board which is then cut into smaller pieces each defining a respective electronic component. A simple example of this process, but with only four electronic components being mounted on the mother board, will be described below.
As indicated in a perspective view of
FIG. 9
, a printed circuit board
111
in which through holes
112
are formed at the prescribed positions is prepared. Wiring patterns
113
are formed on a surface of the printed circuit board
111
, and terminal electrodes
120
(
FIG. 13
) used for surface mounting are formed on a back side of the printed circuit board
111
. The wiring patterns
113
are connected to the terminal electrodes
120
by respective electrodes
118
formed on an inner circumferential surface of respective through holes
112
. The terminal electrodes
120
, the wiring patterns
113
, and the electrodes
118
on the inner circumferential surface of the through holes
112
are typically formed by plating gold on copper. The through holes
112
are filled with solder
119
.
As indicated in
FIG. 10
, a semiconductor element
114
is die-attached to the printed circuit board
111
using epoxy resin or silver paste, and the semiconductor element
114
and the wiring pattern
113
are bonded to each other by a wire
115
of gold or the like. Then, a dam
116
(
FIG. 11
) is provided on a circumferential edge part of the printed circuit board
111
and a thermosetting epoxy resin
117
is applied to the surface of the printed circuit board
111
on which the semiconductor element
114
is mounted. Because the through holes
112
are filled with solder
119
, the applied resin
117
does not enter the through holes
112
. The resin
117
is then hardened through heating, cooling at a room temperature, irradiation of ultraviolet ray, or the like.
The printed circuit board is cut and split along lines passing approximately through center points of the through holes
112
by a dicing blade, and the electrode on the inner circumferential surface of the through holes
112
(as indicated in
FIGS. 12
, and
13
) becomes a side electrode
118
. In this way, a plurality of electronic parts, each including one or more electronic components which are mounted on a circuit board having a terminal electrode
120
on the back side thereof, are obtained.
In conventional electronic parts and in the conventional method for manufacturing those parts, the sealing resin is fully hardened before the mother board is split into smaller pieces. As a result, the resin is very hard when the electronic part is cut by the dicing blade. The inventors have discovered that this causes various problems. Specifically, if the dicing is carried out when the resin has been fully hardened, micro-cracks
122
(
FIG. 14
) can be formed in the resin by the impact of the dicing blade. When micro-cracks
122
are formed, larger cracks are caused as a result of water being absorbed in the micro-cracks
122
and the reliability of the electronic parts is degraded.
Also, in the conventional process after the sealing resin has hardened to its final degree of hardness, the filler and other elements added to the resin for the purpose of changing the coefficient of linear expansion of the resin is exposed in the cut section of the resin. In the condition where the filler, etc., is exposed in the cut section of the resin, the resin surface is in a rough condition having a large number of pores, and there is a problem that water is absorbed from the pores and the reliability of the electronic part is degraded.
In addition, the coefficient of linear expansion of the mother board is different from that of the sealing resin, and the resin shrinks when hardened. As a result, the mother board is warped when the resin is hardened as indicated in a simplified side view in FIG.
15
. In the dicing process, it is necessary that the mother board and the resin be flat to achieve the correct dicing. Because the mother board is warped, the effectiveness of the dicing is suppressed.
SUMMARY OF THE INVENTION
The manufacturing method of the present invention comprises the steps of: semi-curing a thermosetting resin located on the surface of a mother board on which one or more electronic components are located to a stage B condition, at least some of the electronic components being encapsulated in the thermosetting resin; splitting the mother board into individual circuit boards, at least a plurality of the circuit boards having at least one electronic component encapsulated in the resin and mounted on the circuit board so as to form a plurality of electronic parts; and heating at least some of the individual electronic parts so that the thermosetting resin is first melted and is then permanently cured.
Since the mother board is split into individual electronic parts while the resin is in the stage B condition, the mother board is not warped when the splitting takes place. Further, since the mother board is split into individual electronic parts while the resin is in the stage B condition and the resin is subsequently permanently hardened to a final condition after the mother board is split into individual electronic parts, micro-cracks generated in splitting the mother board are removed when the resin is remelted in the process of permanently hardening the resin.
The heating step used to finally harden the resin may be so controlled that the thermosetting resin on the divided mother board melts to cover a portion of a side surface of the divided mother board. In the case, the resin surface is covered with a dense resin film, and the resistance against separation of the resin and the resistance against humidity are improved.
The manufacturing method of electronic parts may further comprises the step of providing a sheet on a surface of said resin before the semi-curing step. As a result, the surface of the resin can be made flat by the force such as the surface tension. This step is particularly useful when a suction device is used to mount the electronic parts.
The thermosetting resin providing on the surface of the mother board may be a pellet shape making the use of a dam unnecessary.
The electronic components may be arranged on the mother board in a matrix to facilitate the splitting process.
The manufacturing method may further comprises the step of arranging the individual electronic parts with intervals therebetween after the splitting step. This ensures that adjacent electronic parts will not be adhered to each other through re-melting of the resin.
An electronic parts according to the present invention comprises: a circuit board; at least one electronic component mounted on the circuit board; and a thermosetting resin provided on the surface of the circuit board so as to seal the at least one electronic component, the thermosetting resin having a top surface layer which has a density greater than the inside thereof. The thermosetting layer may cover a portion of a side surface of the circuit board.
REFERENCES:
patent: 3263304 (1966-08-01), Falanga et al.
patent: 4846032 (1989-07-01), Jampathom et al.
patent: 5635115 (1997-06-01), Konishi et al.
patent: 5640746 (1997-06-01), Knecht et al.
patent: 5729437 (1998-03-01), Hashimoto
patent: 5732465 (1998-03-01), Tokita et al.
patent: 5907477 (1999-05-01), Tuttle et al.
patent: 59-1034 (1984-01-01), None
patent: 393119 (1991-04-01), None
Fujimoto Isamu
Tatsumi Tetsuo
Yaso Tohru
Chang Rick Kiltae
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Young Lee
LandOfFree
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