JPH03162972A - Thermal head - Google Patents

Abstract

PURPOSE:To improve reliability at a bonding part by placing a drive control IC chip for driving a plurality of heat generating resistors together with a plurality of heat generating resistors and conductors on a board having a specific thermal expansion coefficient, and covering connecting bumps to be connected with synthetic resin having specific thermal expansion coefficient. CONSTITUTION:A plurality of heat generating resistors 3 and conductors are formed on a board 4 having thermal expansion coefficient of 12 X 10-<6> deg.C or lower, and a drive control IC chip 1 for driving the resistors 3 are placed thereon. The input/output terminal of the chip 1 and the conductors are connected with solders as connecting bumps 8 by a face-down bonding system, and covered with synthetic resin having thermal expansion coefficient of 25 - 30 X 10-<6>/ deg.C. Accordingly, since a stress generated at the bump due to the difference of the coefficients of the board 4 and a silicon wafer for forming the IC 1 is alleviated and dispersed by the resin, a stress by the coefficient difference between both is reduced. Thus, the reliability of bonding is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates primarily to a thermal head used in a thermal printing and recording device.

(b) Prior Art FIGS. 5 to 7 show the overall structure of a conventional thermal head. In the conventional example shown in FIG. 5, a drive control integrated circuit chip (hereinafter referred to as IC) +01 is mounted on an IT printed wiring board +02 (usually a glass epoxy board, hereinafter referred to as PWB) with adhesive paste (as shown in the figure). Guibond by (not).

The heating resistor 103 is formed on a ceramic substrate 104, and the ceramic substrate +04 and PWB l 02 are pasted onto a heat sink 105. Next, the ICIO for drive control
The output terminal 106 of I is an individual electric wire wired to the heating resistor +03 on the ceramic substrate 104! +07 and gold wire +0
Connected by 8. In addition, the human power terminal l06a on the drive control ICIOI is connected to the electrode 10 on the PWB IO2.
9 and gold wire 108a, electrical connection is made across the wire bond. Then, drive control ICIOI and gold wire l
08. +08a is protectively coated with silicone resin 113.

In another conventional example shown in FIG. 6, a drive control IC 201 is firmly bonded onto a ceramic substrate 204 using an adhesive paste (not shown).

A heating resistor 203 and the like are formed on a ceramic substrate 204 . Output terminal 2 on drive control IC20+
06 is a heating resistor 203 on a ceramic substrate 204.
The individual electrodes 207 and the gold wires 208 are connected to each other. In addition, the input terminal 20 on the drive control IC 201
6a is the electrode 209 on the ceramic substrate 204 and the gold wire 2
08a for wire bonding and electrical connection.

Ceramic substrate 204 is FP with Ura hard plate 210 attached.
C (flexible board) 2l1 is pressed onto the heat sink 205 through the rubber 212,
The ceramic substrate 204 and the FPC 2 11 are electrically connected. Then, drive control IC 201 and all lines 20
8.208a is protectively coated with Noricone resin 213.

Comparing the configurations in Figures 5 and 6, the thermal head in Figure 5 uses less of the expensive ceramic substrate than the one in Figure 6, and has a cheaper configuration in terms of materials. . However, in the configuration shown in FIG. 6, a system has been put into practical use in which the electrical connection by wire bonding is replaced by electrical connection by bumps (hereinafter referred to as face-down bonding).

Figure 7 shows the structure. Bump 30 for connection on the electrode
8 (solder-mounted configuration) for drive control IC30
1 is a ceramic base material 3 on which a heating resistor 303 is formed.
The output terminal 306 of the drive control IC 30l is mounted on the f2 individual electrode 307 by face-down bonding, and the output terminal 306 of the drive control IC 30l is wired to the heating resistor 303.
8 on the ceramic substrate 304. Further, the input terminal 306a of the drive control IC 301 is electrically connected to the electrode 309 on the ceramic base 304. Drive control IC 301 and ceramic substrate 304
Evokino resin 313 is sealed between the connection bumps 3
08 is protective coated.

A reinforcing plate 310 is attached to the ceramic substrate 304.
The PC3 1 1 is pressed onto the heat dissipation temporary 305 via the rubber 312 and is pressed into contact with the ceramic substrate 304 and the FPC.
3 1 1 is electrically connected.

(c) Problem 4 to be solved by the invention Conventionally, in order to shape the heat generating resistor part, it was necessary to apply heat of at least 500 to 600 degrees Celsius in the manufacturing process. When in use, the area near the heating resistor must be heat resistant to about 400°C, so a ceramic substrate is used as an insulating substrate that meets this requirement.
! There are 1. However, ceramic substrates are expensive;
In addition, because of poor workability, the structure of the thermal head is a combination of a ceramic base material and PWB or FPC, as described above. In contrast, the applicant of the present application proposed a heating resistor on an insulating substrate formed by impregnating a heat-resistant cloth with a heat-resistant resin (for example, an insulating substrate made of glass fiber impregnated with polyimide resin) instead of a ceramic substrate. A thermal head in which a connecting wiring layer and a heating resistor are formed for use and control circuit components, and control circuit components are integrally mounted on the substrate has already been filed as Japanese Patent Application No. 1-86480.

By the way, for the electrical connection between the input terminal of the drive control IC and the electrode on the insulating substrate, as mentioned above, there are two methods: wire bonding method and face-down bonding method. Comparing both methods, it is found that the wire bonding method and the face-down bonding method are used as shown below. There are advantages to the bonding method.

■The wire bonding method requires the drive control IC to be bonded onto the board in advance, but the face-down bonding method requires the drive control IC to be bonded on the board in advance.
There is no need to carefully bond C onto the substrate, and the face-down bonding itself serves as both die bonding and wire bonding, which can shorten the manufacturing time.

■With the wire bonding method, each electrode of the drive control IC and each II pole of the board must be wire-bonded one by one in sequence, and it takes about 0.2 seconds to bond one wire. Printing density of 8 dots/m equipped with 27 drive control ICs with 89 input/output electrodes.
m, printing width 216 mm (A4 type), wire bonding time is 0.2 seconds x 89 x 27 = 48
It takes 0.6 seconds #8 minutes. On the other hand, in the face-down bonding method, all the input/output electrodes on the IgI drive control IC can be bonded to one electrode on the substrate at once, so one drive control I
Bonding of C takes about 2 seconds, and for example, the printing density is 8 dots with 27 drive control ICs as above.
/mm, printing width 216mm (A4 type): The bonding time is 2 seconds x 27 = 54 seconds, which is about 1/8 the time of the wire bonding method. Print density is even higher at 12 dat/mm, I 6
dat/mm, about 1/12 of the wire bonding method. It's amazing that it takes about 1/16th of the time.

■With the wire honding method, external forces after honding may cause the honding wire to bend or fall.
The face-down bonding method does not require bonding wires and does not cause short-circuits between electrodes.

■With the wire bonding method, if the IC is defective, its I
It is almost impossible to replace only IC, and the entire head will be defective, but with the face-down bonding method, it is possible to replace the IC, and the entire head will not become defective.

Due to the advantages of face down bonding as mentioned above,
A drive control IC is bonded by a face-down bonding method onto an insulating substrate formed by impregnating a heat-resistant cloth with a heat-resistant resin.

However, the coefficient of thermal expansion of an insulating substrate formed by impregnating a heat-resistant cloth with a heat-resistant resin is slightly larger than that of the conventional ceramic base W (2.5xlO-'/°C), which is 12x
10-'/'C, and the silicon wafer (2.6
Due to the difference in expansion coefficient between This is unsatisfactory.

This invention was made in consideration of these circumstances,
The present invention provides a thermal head in which the bonding part has high reliability when a drive control IC is mounted by a face-down bonding method on an insulating substrate formed by impregnating a heat-resistant cloth with a heat-resistant resin.

(2) Means for Solving the Problems This invention forms a plurality of heating resistors and conductors on a substrate having a coefficient of thermal expansion of 12×10-'/°C or less, and drives the heating resistors. It is equipped with a drive control IC chip, and uses solder as a connection bump to connect the drive control IC chip.
The input/output terminals of the C chip and the conductor are connected by a face-down bonding method, and the connection bumps are
This is a thermal head coated with a resin having a thermal expansion coefficient of 30 x 10-''/°C.

Preferably, the substrate is an insulating substrate formed by impregnating a heat-resistant cloth with a heat-resistant resin. For example, 60-Sn solder is used for the face-down bonding connection bump. In addition, epoxy resin can be used as the hewei resin.

(e) Effect Thermal expansion coefficient with multiple heating resistors 12X 10-'
A drive control IC is mounted on an insulating substrate with a temperature of /°C or less by a face-9-down bonding method, and bumps formed by solder are used for connection. moreover,
The bump of the connection portion is covered with Evokin resin sealed between the drive control IC and the insulating substrate. The Evokino resin has strong adhesion to the drive control IC, the insulating substrate, and the bumps of the connection portion, and has a coefficient of thermal expansion close to that of solder 2, which forms the bumps by adjusting the filler.
It is set at 5 to 3oX1o-6,/°C. Therefore, the stress generated in the bump portion due to the difference in thermal expansion coefficient between the insulating substrate and the silicon wafer forming the drive control IC is relaxed and dispersed by the synthetic resin, so that the stress caused by the difference in thermal expansion between the two is reduced. becomes smaller.

As a result, even if the drive control IC is mounted on the insulating substrate by the face-down bonding method, the reliability of the bonding portion is improved.

(f) Example This invention will be explained in detail based on the example shown in the drawings. This invention is not limited by this.

10 FIG. 1(a) is a plan view of a thermal head according to an embodiment of the present invention, FIG. 1(b) is a sectional view of the thermal head shown in FIG. 1, and FIG. 2 is a portion of FIG. 1(a). The enlarged view, FIG. 3, is a partial enlarged view of FIG. 1(b).

In FIG. 1, the drive control ICI is mounted with a resistor 3 on an insulating substrate 4 by face-down bonding. The bump 8 made of 60-Sn solder connects the drive control rCl output 111+1 electrode (
The terminal) 6 is connected to an individual electrode 7 to the heating resistor 3, and the input side electrode (terminal) 6a of the drive control ICI is connected to an electrode 9 on the insulating substrate 4. Here, insulating substrate 4
The material is formed by impregnating a heat-resistant cloth with a heat-resistant resin. For example, a material made of glass fiber impregnated with a polyimide resin and having a coefficient of thermal expansion of 12X to -6/'C or less is used.

Between the drive control rc1 and the insulating board 4 is an epoxy resin l3.
is encapsulated, thereby providing the connection bump 8 with a protective coating.

Here, the epoxy resin 13 has strong adhesion +1 to the drive control IC 1, the insulating substrate 4, and the bumps 8, and by mixing filler such as Si02, the bumps 8 are formed due to its thermal expansion coefficient. A coefficient of thermal expansion of 25 to 30XlO-'/°C, which is slightly larger than that of 80-Sn solder, is used. In addition to the drive control ICI, electrical components and connectors for connection with external circuits are soldered and mounted on the insulating substrate 4, and the substrate 4 is pasted onto the heat sink 5.

FIG. 2 shows how the drive control IC1 is mounted on the board 4. This figure is viewed from above the mounting part of the drive control ICI, and although the bump 8 is not visible, it is shown by a solid circle line for convenience. [Cl for drive control] is made of a Si chip, has a size of approximately 7 mm x I mm x 0.6 mm, and is provided with 64 output side electrodes 6.

FIG. 3 shows a cross section taken along line AA in FIG. 2. The bump 8 has a drum-shaped shape with a diameter of about 100 μm, and is made of Evokin resin.
It is completely covered by 3. Here, the thermal expansion coefficient for drive control [C (Si chip) is 2.6X 10-8/℃
, bump 8 (60-Sn solder) is 25xlQ-s/
°C, epoxy tree 11N+3 (:7ira-R combined epoxy)
is 30X1G-@/℃, and the insulating base 4 (glass fiber impregnated with heat-resistant resin) is +2×10-'/'
C, and a thermal shock cycle test was conducted.

The thermal expansion coefficients of Evokin resin l3 and insulating group Kari 4 are 25 to 30 x 10-6/°C and l2xlO, respectively.
It is preferable that the coefficient of thermal expansion be within the range of −'/°C or less, and the smaller the value within that range, the more advantageous it is in terms of reliability. However, it was confirmed by the thermal shock cycle test results shown in FIG. 4 that the reliability was greatly improved compared to the conventional method.

FIG. 4(a) shows the test results of this example, with no defects occurring up to 500 thermal shock cycles. (c) is without epoxy resin encapsulation, (b) is a conventional epoxy resin (thermal expansion coefficient 65X 10-6/'C
), and (mouth) is somewhat improved from (c) by the inclusion of epoxy resin, but both are 30
The defective rate is close to 0 cycles or 100%.

In this example, a heat-resistant cloth is impregnated with a heat-resistant resin (13) and a heat-resistant substrate is used. It goes without saying that the present invention is equally applicable to the case where f2 is used.

(G) Effects of the Invention According to the present invention, when a drive control IC is mounted by face-down bonding onto an insulating substrate formed by impregnating a heat-resistant cloth with a heat-resistant resin, the reliability of the bonding portion is improved. Therefore, a highly reliable thermal head can be provided without using an expensive ceramic substrate.

[Brief explanation of the drawing]

FIG. 1(a) is a partial top view of a thermal head showing one implementation of this invention, FIG. 1(b) is a sectional view of FIG. 1(a), and FIG. Partially enlarged view, Figure 3 is a sectional view taken along line A-A in Figure 2, Figure 4 is a graph showing the thermal shock cycle test results, Figures 5(a), 6(a) and 7(
a) is a top view showing the conventional example, FIG. 5(b), FIG. 6(b)
) and FIG. 7(b) are cross-sectional views of FIG. 5(a), FIG. 6(a), and FIG. 7(a), respectively. - Low fever antibody, 4. Insulating substrate, 8... - Connection bump, l3...Evokin resin. -15-1

Claims (1)

[Claims] A plurality of heat generating resistors and conductors are formed on a substrate having a thermal expansion coefficient of 1,12 x 10^-^6/°C or less, and a drive control IC chip for driving the heat generating resistors is mounted. , connect the input/output terminals of the drive control chip and the conductor using solder as connection bumps by a face-down bonding method, and connect the connection bumps to 25 to 30
A thermal head coated with a synthetic resin having a coefficient of thermal expansion of ×10^-^6/°C.