JPH0732632A - Circuit board connection terminal laminated structure and thermal head using the structure - Google Patents

Abstract

PURPOSE:To obtain a connection terminal laminated structure of a circuit board generating no crack due to thermal expansion difference by forming a fragile coating layer on the upper surface of a first circuit board and laminating a connection terminal composed of a metal on the upper surface of the coating layer and providing an elastic layer between the coating layer and the connection terminal of the first circuit board. CONSTITUTION:A fragile coating layer 22 is formed on the upper surface of a first circuit substrate 20 and a connection terminal 60 (70) composed of a metal is laminated to the upper surface of the coating layer 22 and the connection terminal 60 (70) and the connection terminal 90 of a second circuit substrate 80 are thermally fused through solder. In the laminated structure of the connection terminal of the circuit board, an elastic layer 1 is provided between the coating layer 2 and the connection terminal 60 (70) of the first circuit board 20. As a result, even when two circuit boards different in the coefficient of thermal expansion are bonded under heating and pressure by solder, a problem such as a crack or the like due to thermal expansion difference is not generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a connection terminal structure of a laminated circuit board formed by laminating materials having different coefficients of thermal expansion and an improvement of a thermal head using the structure.

[0002]

2. Description of the Related Art A connection terminal structure of a conventional laminated circuit board shown in FIG. 5 will be described below by taking a general thermal head shown in FIGS. 6 to 7 as an example.

In FIGS. 6 and 7, reference numeral 10 denotes a heat dissipation plate made of a metal plate such as aluminum, and reference numeral 20 denotes a head substrate mounted on the upper surface of the heat dissipation plate 10 with an adhesive material or a double-sided tape.

The head substrate 20 comprises a ceramic plate 21 having a plate thickness of about 1 mm, and a glaze layer 22 containing glass of about 70 μm as a main component on the upper surface of the plate 21.
Are coated. The glaze layer 22 plays a role of heat storage of a heating resistor 30 which will be described later and smoothes the upper surface of the plate 21 so that a power supply wiring 50 and a signal wiring 51 which will be described later are made of inorganic gold and / or organic gold paste. Is formed by printing and baking, it is provided so that printing defects do not occur.

On the upper surface of the glaze layer 22, a strip-shaped heating resistor 30 is formed in a straight line along the longitudinal direction of the head substrate 20, and the heating resistor 30 generates heat. A plurality of drive ICs 40 to be controlled are mounted in a line along the heating resistor 30. Further, the heating resistor 3 is formed on the upper surface of the glaze layer 22.
The print power supply wiring 50 for 0 is formed.

Then, on one side edge of the upper surface of the head substrate 20, a power source, a clock signal, a latch signal or an enable signal wiring 51 for each driving IC 40 is provided.
And a connection terminal 60 (70) made of a silver-paradium-based conductive paste that is connected to the print power wiring 50.
Is formed by printing and baking.

As described above, at the place where the connection terminal 60 (70) is formed on the head substrate 20, the ceramic plate 21, the glaze layer 22, the wirings 50 and 51, and the connection terminal 60 (70) are laminated. It has a structure. (See Figure 5)
On the other hand, reference numeral 80 indicates a flexible circuit board made of soft synthetic resin, and the flexible circuit board 80 is formed with connection terminals 90 connected to each of the plurality of connection terminals 60 (70) on the head board 20. In addition, a wiring pattern (not shown) for connecting each of the connection terminals 90 to the socket 100 fixed to the flexible circuit board 80 is formed.

Reference numeral 110 is a protective film such as glass for the heating resistor 30, and reference numeral 120 is each drive IC 40.
The synthetic resins for packaging are shown respectively.

The flexible circuit board 80
With respect to one side edge in the longitudinal direction of the head substrate 20, each connection terminal 90 in the wiring pattern of the flexible substrate 80 is connected to the connection terminal 6 in the head substrate 20.
0 (70) so as to come into contact with each other, and then each connecting terminal 90 on the flexible substrate 80 is heat-welded to each connecting terminal 60 (70) on the head substrate 20 by soldering.

As shown in FIG. 6, this soldering is performed by connecting terminals 90 of the flexible substrate 80 and the head substrate 20.
Of either or both of the connection terminals 60 (70) of FIG. 1 are coated with a solder paste in advance or a solder film is formed by solder plating, and then the flexible circuit board 8
0 is superposed on the head substrate 20 and is heated by being pressed with an appropriate pressure by the vertical pressing and heating means P shown in FIG. 6. By such soldering, the flexible substrate 80 Connect each connection terminal 90 to each connection terminal 60 (70) on the head substrate 20.
Of each of which is heat-welded. The temperature during this heat welding is usually 230 to 250 degrees Celsius.

[0011]

A ceramic plate 21, a glaze layer 22, wirings 50 and 51, and connection terminals 60 (70) are formed on the head substrate 20 where the connection terminals 60 (70) are formed. When the solder is heat-welded by the heating means P, the glaze layer 22 in the laminated structure, and the wirings 50 and 51 and the connection terminals 60 (70) on the glaze layer 22 in the laminated structure are formed. Due to the difference in the coefficient of thermal expansion between the two, stress is generated between the two, and there is a problem that cracks occur in the relatively thin and brittle glaze layer 22.

Due to this crack, the connection terminal 60 (7
Delamination occurs in the 0) portion, and the wiring 50, 51 and the connection terminal 60 (70) and the connection terminal 90 of the flexible substrate 80 are thermally welded in a disconnected state. there were.

In particular, for example, in a movable (serial) thermal head, the head substrate 20 moves and prints on a printing object (paper, thermal paper, etc.), so the flexible substrate 80 and the head substrate 20 are connected. Overload due to the movement of the head substrate 20 is easily applied to the location, and the occurrence of the crack often causes a failure such as disconnection.

An object of the present invention is to prevent the occurrence of cracks as described above and solve all the above problems.

[0015]

In order to solve the above problems, the present invention takes the following technical means.

That is, a first circuit board and a brittle coating layer are formed on the upper surface of the first circuit board, and
In the connection terminal laminated structure of the circuit board, the connection terminal made of metal is laminated on the upper surface side of the coating layer, and the connection terminal and the connection terminal of the second circuit board are heat-welded via solder. An elastic layer is provided between the cover layer and the connection terminal of the first circuit board.

Further, a brittle glaze layer is formed on the entire upper surface of the ceramic head substrate, and a strip-shaped heating resistor is provided on the upper surface of the glaze layer, and the heating resistor is selectively driven to generate heat. A driving IC, the heating resistor, the driving IC, and a connection terminal for deriving an external signal or the like are provided on the upper surface of the glaze, and the heating resistor, the driving IC, and the connection terminal are electrically connected by wiring. On the other hand, in the thermal head in which the connection terminals of the head substrate and the connection terminals of the flexible substrate are heat-welded with solder while connecting, an elastic layer is provided between the glaze layer and the connection terminals of the head substrate. It is characterized by being provided.

The elastic layer is located between the brittle coating layer or glaze layer and the connection terminal, relaxes the stress generated during heat welding with solder, and is brittle in the coating layer or glaze. Any material may be used as long as it has elasticity enough to prevent cracks from being generated in the layer. For example, the elastic layer may be formed by printing and firing a mix-bond type paste described later, or may be formed by sputtering in a high-pressure atmosphere so that an appropriate hollow portion is contained in the layer.

[0019]

According to the present invention having the above-mentioned structure, between the coating layer or the glaze layer formed on the first circuit board or the head board made of ceramic and the connection terminal of the second circuit board or the flexible board. Since the elastic layer is provided on the glaze layer, the elastic layer is used to heat the connection terminals of the both boards and the connection terminals of the second circuit board or the flexible board by soldering. The stress caused by the difference in thermal expansion coefficient from other layers such as connection terminals is relaxed to prevent cracks from occurring.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention applied to a thermal head will be specifically described below with reference to the drawings.

Since the basic structure of the thermal head used in this embodiment is the same as that shown in FIGS. 6 and 7, detailed description will be omitted.

1 and 2 show an embodiment of the present invention. 2 is an enlarged cross-sectional view of a main part of the vicinity of the connection terminal as seen from the arrow A in FIG. 6, and FIG. 1 is a BB cross-sectional view of FIG.

In the figure, 20 is a head substrate which is an example of a first circuit board, 21 is a ceramic plate, 22 is a glaze layer, 50 (51) is wiring, 60 (70) is a connecting terminal, and 80 is a connecting terminal. Is a flexible board which is an example of the second circuit board, and 90 is a connection terminal of the flexible board 80, which has the same configuration as the above-mentioned conventional example. A solder layer (not shown) is interposed between the connection terminal 60 (70) and the connection terminal 90.

Reference numeral 1 denotes an elastic layer according to the present invention. The elastic layer 1 is formed by wiring 50 (51) printed on the surface of the glaze layer 22 as a brittle coating layer and a connecting terminal 60.
Mixed bond type containing silver or gold particles between (70) (for example, product number DD12 manufactured by Kyoto Elec Co., Ltd.
04, etc.) is formed by printing and baking. When such a mixed bond type paste is printed and baked to form the elastic layer 1, the layer has a porous network structure and can be made a layer having elasticity. In other words, the mixed bond type paste is a mixed paste of glass particles, metal particles and organic substances, and when the paste is baked at about 800 ° C., the contained organic substances disappear by evaporation and the like. Minute cavities are created where the organic matter was. Of course, the conductivity is not lost even if a cavity is formed.

In this embodiment, a mixed bond type paste is adopted as the elastic layer 1, but the elastic layer 1 is not limited to this, and is suitable (to the extent that the stress generated by the difference in thermal expansion between the glaze layer and the wiring can be absorbed). Any material can be used as long as it has sufficient elasticity. For example, the elastic layer 1 can be formed by the thin film forming method described in a modified example described later.

The wiring 50 (51) is made of organic gold.
The elastic layer 1 is formed so as to cover the wiring 50 (51), and a paste containing silver and palladium mixed is printed and baked on the elastic layer 1 to form a connection terminal. 60 (70) is formed.

In this way, the wiring 50 (51) is connected to the elastic layer 1
The wiring 50 (51) and the solder come into direct contact with each other, so that the occurrence of wire breakage due to the solder being eaten can be alleviated.
That is, the wiring 50 (51) becomes a film of pure gold only after firing, and the solder and gold are very easily blended together, so that the solder H becomes a ball shape as shown in FIG. The film M may be consumed, and the gold film M may be peeled off from the substrate K and dissolved and disappear, resulting in defective adhesion or disconnection with solder. The elastic layer 1 also contains silver or gold, which is easily compatible with solder. However, since impurities such as glass frit are mixed in the elastic layer 1, the layer is considerably thicker than the wiring 50 (51). The influence of the above-mentioned problem such as disconnection due to solder leaching is alleviated as compared with the wiring 50 (51) formed of pure gold only. However, in order to prevent the above-mentioned problem due to solder leaching, the palladium element or the like may prevent solder leaching as in the case where the silver-palladium paste is used as the solder connecting terminal 60 (70). It is preferable to contain an impurity which suppresses prevention.

Further, as described above, the elastic layer 1 is not formed so as to exactly overlap the surface of the wiring 50 (51), but is formed so as to completely cover the wiring 50 (51). When gold and silver form an alloy, the electric resistance increases, and it is because it is desired to reduce the overlapping portion.

FIG. 4 shows a modified embodiment of the present invention. In this modified embodiment, the following method, which is different from the method of forming the elastic layer 1 of the above-described embodiment, is adopted, and the formation position of the elastic layer 1 is connected to the connection terminal 60 (70) and the wiring 50 (5).
1) except that the glaze layer 22 and the wiring 50 (51) are different from each other, and the other structure is the same as that of the above-described embodiment.

The elastic layer 1 in the present modified example is formed by vapor-depositing metal particles such as gold in a high pressure gas by a sputtering method to form a film having elasticity. Normal,
Sputtering is performed, for example, in an argon gas atmosphere at a gas pressure of 3 × 10 ⁻³ torr.
Form by raising to 10 ^-2 .

When the gas pressure is increased in this manner, when the metal particles are sputtered on the deposition target portion (the surface of the glaze layer 22 forming the connection terminal 60 (70)), the particles such as the argon gas are taken in. As a result, the formed elastic layer 1 can be a porous film containing gas particles.

Further, when the elastic layer 1 is directly provided on the glaze layer 22 as in this modified embodiment, the stress generated during the thermocompression bonding of the solder is efficiently transmitted to the glaze layer. It is preferable because it can be absorbed, but if it is formed between the connection terminal 60 (70) to which the solder is directly in contact and the glaze layer 22, it may be formed between any layers to some extent.
It is possible to prevent the occurrence of cracks. However, when the elastic layer 1 is partially formed in the lower layer of the connection terminal, it is easier to form the elastic layer 1 in the upper layer of the wiring 50 (51) for the convenience of the manufacturing method.

Further, in this embodiment, the glaze layer 22 is 70 μm, the connection terminal 60 (70) is 6 μm, the wiring 50,
51 is 0.6 μm, the elastic layer 1 is 12 μm, which is sufficiently thicker than the above layers, so that the stress due to the difference in thermal expansion can be reliably relaxed.

A flexible substrate 80 is soldered to each of the head substrate 20 (hereinafter, referred to as A type) having the elastic layer 1 formed thereon and the conventional head substrate 20 without the elastic layer 1 (hereinafter, B type). Thermo-compression bonded, both substrates 2
When the adhesion states of Nos. 0 and 80 were compared by a tensile test (tensile load of 1.5 kg), the following results were obtained. The tensile load is set to be significantly larger than the load that can be normally applied (the load that can normally be applied is about 0.3 kg). Usually, in the finished product, a resin coat for adhesion reinforcement is generally provided at the position where the head substrate 20 and the flexible substrate 80 are solder-bonded, but the main pulling test However, no resin coat is applied.

After thermocompression bonding, the peeling rate between the connection terminal 60 (70) of the head substrate 20 and the connection terminal 90 of the flexible substrate 80 by the tensile test is about 8.7% for the A type and about 100% for the B type. It was 56%. The peeling rate means that 10 thermal heads are used, and the glaze layer 22 and the connection terminal 60 (70) of each head substrate 20 are used.
And the total number of peelings generated between and is divided by the total of the connection terminals 60 (70) of all the thermal heads.

Next, a reliability test (125 ° C. → 25 ° C. →
After the process of repeating minus 30 ° C for 100 cycles),
When the same test as described above was performed, the peeling rate was about 45% for the A type and about 100% for the B type.

In the present embodiment, the brittle layer has been described as being applied to the glaze layer containing glass as a main component, but the present invention is not limited to this, and any thin and brittle layer can be applied. Is.

[0038]

According to the present invention having the above-described structure, the connection terminals of the coating layer or the glaze layer formed on the first circuit board or head board made of ceramic and the second circuit board or the flexible board are formed. Since an elastic layer is provided between the contact layer and the connection terminal of the both boards and the connection terminal of the second circuit board or the flexible board by soldering, the elastic layer is used for the gray layer. The stress caused by the difference in thermal expansion coefficient between the insulating layer and other layers such as connection terminals is absorbed and relaxed by its elasticity to prevent cracks from occurring.

Since the generation of cracks can be prevented in this way, when the thermal head is used in a connecting structure for connecting a connecting terminal between a head substrate and a flexible substrate such as a thermal head, the thermal head is of a movable type. Even
Holds the connection between the head substrate and the flexible substrate,
It is possible to eliminate connection peeling due to cracks.

[Brief description of drawings]

FIG. 1 is a sectional view taken along line BB of FIG.

FIG. 2 is an enlarged cross-sectional view of a main part of a connection terminal 2 viewed from an arrow A in FIG.

FIG. 3 is an explanatory diagram of an example of the present invention.

FIG. 4 is a perspective view showing a modified embodiment of the present invention.

5 is a cross-sectional view showing a connection terminal laminated structure of a conventional circuit board as seen from an arrow A in FIG.

FIG. 6 is a side view showing a thermo-compression state of a general thermal head.

FIG. 7 is a perspective view of FIG.

[Explanation of symbols]

 1 Elastic Layer 22 Glaze Layer 20 Head Substrate 60, 70, 90 Connection Terminal 80 Flexible Substrate

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location 9168-4M H01L 21/92 U

Claims (2)

[Claims] 1. A first circuit board, a brittle coating layer is formed on an upper surface of the first circuit board, and a connection terminal made of metal is laminated on the upper surface side of the coating layer.
In a connection terminal laminated structure of a circuit board in which the connection terminal and the connection terminal of the second circuit board are heat-welded via solder, an elastic layer is provided between the cover layer and the connection terminal of the first circuit board. A connection terminal laminated structure for a circuit board, which is provided. 2. A glaze layer is formed on the entire upper surface of a ceramic head substrate, a strip-shaped heating resistor is provided on the upper surface of the glaze layer, and a drive IC for selectively heating the heating resistor. , The heating resistor, the drive IC, and the gray
A connection terminal for deriving an external signal or the like is provided on the upper surface side to electrically connect the heating resistor, the drive IC and the connection terminal by wiring, and connect the connection terminal of the head substrate and the flexible substrate. A thermal head comprising a terminal and a terminal that are heat-welded with solder, wherein an elastic layer is provided between the glaze layer and the connection terminal of the head substrate.