JPS63260059A - Module structure of contact type image sensor - Google Patents

Abstract

PURPOSE:To prevent light from attenuating or so due to each light transmission factors and to prevent sensitivity from being lowered due to shortage in the quantity of light into a sensor, by junctioning a sensor chip on a side of a circuit board, where the sensor chip is driven and a signal from the sensor chip is processed, in a module structure of an adhesion type image sensor and next by mounting the juncture on the circuit board. CONSTITUTION:A group of electronic components 2, which form a circuit where a sensor is driven and a signal from the sensor is processed, are junctioned on a printed circuit board 1 by the use of solder 3 or the like. A sensor chip 4 is junctioned on a side of the printed circuit board 1 in this circuit block A by the use of an adhesive 31. A wire bonder and a bonding wire 8 are used to electrically junction a bonding pat 6 of the sensor chip with a bonding pat 7 for wiring on the printed circuit board 1. In succession, a molding agent 10 is provided to compose a sensor module. Since an organic material is not contained in an incident optical path, accordingly a stable sensor characteristic can be maintained to be very small in a change of its transmission factor with the lapse of time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a module configuration of a contact type image sensor.

[Prior Art] Conventionally, an image sensor element called a linear image sensor or line sensor has a structure in which a light receiving element, etc. is formed on only one side of a base substrate of glass (for example, quartz glass or borosilicate glass). ing.

Light enters this light-receiving element and it operates as an image sensor.There are two methods of entering the light: one is through the glass, and the other is not through the glass. There is.

The method in which light enters the light-receiving element without passing through glass is called the top method, and its cross-sectional structure is shown in Figure 2.The method in which light enters the light-receiving element through glass is called the bottom method, and its cross-sectional structure is shown in Figure 2. The cross-sectional structure is shown in Figure 7753.

These conventional techniques will be described in more detail. In the top method (FIG. 2), first the electronic component 2 is bonded to the printed wiring board l with solder 3, and then the sensor chip 4 is attached to the printed wiring board l.
A circuit block A is formed to drive the circuit and perform signal processing. On top of this circuit block A, a sensor chip 4 is adhered to a desired position on the printed wiring board 1 using a die attach agent 5.

The bonding area 6 of this sensor chip and the bonding area 7 of the printed wiring board 1 are connected with a bonding wire 8 using a well-known bonder or the like to establish an electrical connection.

After the connection is completed, the elements 9 such as the light receiving element on the surface of the sensor chip 4 and the bonding wires 8 are covered with a molding agent 10 to protect them from the external environment.Since the molding agent 10 is initially in a liquid state, when filling Paste the mold frame 11 on the printed wiring board 1 with adhesive 12 to prevent it from flowing out.
The molding agent IO is heated after filling, UV irradiation, etc.
Change from liquid to solid, however, molding agent lO
must be transparent.

In the bottom method (Fig. 3), first, the glass substrate 2 is
1. The sensor chip 4 is bonded to a glass plate (this is a substrate with electrical wiring on the surface) using an optical die attach agent 22.

Thereafter, the bonding wire 8 is bonded to the glass substrate 21 using a bonder. Then, a rubber frame 23, which serves both as a mold frame and a connector frame, is bonded with adhesive 12.

The mold filling groove of the rubber frame 23, which is a mold frame, is filled with molding agent 10 and cured, and the circuit block A that drives the sensor chip 4 and performs signal processing is electrically connected with the connector 24 to form a sensor module. It is configured as

[Problems to be Solved by the Invention] However, the conventional sensor module configuration has several problems.

In terms of the top method, one reason is that the light (hu) enters from the direction shown in Figure 2, so if the surface shape of the molding agent 10 (the top surface of the sensor chip) is not optically flat, the light reception will be difficult. A clear image is not formed on the surface of the element 9, and the light transmission pressure of the molding agent IO is low.
The sensitivity of sensor 9 decreases. Furthermore, if surface and interface reflections are included, the amount of light will drop to about 80% of the amount of light that enters directly.

Furthermore, in terms of mounting space, a large amount of space is taken up as it is necessary to attach mold frames and the like.

In the bottom method, there is a problem with the connector, and the electrical connection between the circuit block A and the glass substrate 21 cannot be established unless the connector is always pressed into contact.
When assembling a sensor unit, it is necessary to always consider the pressure welding structure.

Also, since light enters from the glass substrate 21 side, the light enters the surface of the glass substrate 21, the interface between the glass substrate 21 and the die attach agent 22, and the interface between the sensor chip 4 and the die attach agent.

Due to light attenuation due to surface reflection and light attenuation 1 due to the light transmittance of each of the sensor chip 4, die attach 22, and glass substrate, the sensitivity of the sensor 9 decreases due to an insufficient amount of light.

Because of these light attenuations, the speed of the sensor had to be slowed down to accommodate user needs.

Furthermore, in terms of mounting space, it takes up a lot of space as the glass substrate mold frame and the circuit block must be integrated into one.

Since the circuit board is located directly above the sensor element 9, sufficient measures must be taken to prevent noise from the circuit, leaving many problems unsolved.

[Means for Solving the Problems] Therefore, in order to solve the conventional problems, in the module structure of the contact type image sensor, on the side of the circuit board that drives the sensor chip and processes signals from the sensor chip, A module structure of a contact image sensor characterized by bonding a sensor chip and mounting the sensor chip on a circuit board.

[Actual Example] FIG. 1 shows a cross-sectional view of the structure of a module of a coherent wave image sensor according to the present invention.

First, printed wiring board l (in the present invention, FR-4
A group of electronic components 2 forming a circuit for driving the sensor and processing signals from the sensor are bonded with solder 3 to the side surface of the printed circuit board 1 of this circuit block A.

The sensor chip 4 is bonded with an adhesive 31. After the bonding is completed, the bonding pad 6 of the sensor chip and the bonding pad 7 of the wiring of the printed wiring board 1 are bonded using a well-known wire poredder and bonding wire 8. to join. Thereafter, a molding agent 10 is applied to form a sensor module.

This will be explained in more detail using figures. The steps from Figure 4 to Figure 9 are the steps required to complete the present invention (Figure 1).

First, as shown in FIG. 4, a printed wiring board 1 is formed by applying electrical wiring to a base material containing glass fiber or the like to provide rigidity and having a coefficient of thermal expansion as small as possible.
In the present invention, FR-4 and G-10 were used, which is commonly called Gala Evo. However, there are other materials that can be used for this printed wiring board, such as injection substrates, metal substrates, ceramic substrates, etc., regardless of the method of formation. , Gara Evo was chosen because of its ease of acquisition, processing, and cost.

Next, j! As shown in Fig. 85, active components and passive components 2 are bonded with solder 3 to form a circuit that drives the sensor, inputs signals to the sensor, and processes signals from the sensor. However, if electrical bonding is possible, there are other methods such as using a conductive adhesive or using an anisotropic conductive film with directional conductivity.

Thereafter, as shown in FIG. 6, a film 41 coated with an adhesive 42 is attached. When bonding, a rubber roller can be used to prevent air bubbles from entering the interface with the printed circuit board l, allowing for convenient bonding.In the present invention, irradiating the adhesive 42 with ultraviolet light, which is convenient, increases the adhesive strength. We used a material that exhibits extreme deterioration, making it easy to peel off after forming the sensor module. Further, as the film 41, a polyester film having relatively good heat resistance was used. This film is not limited to polyester film, but any film can be used as long as it has satisfactory heat resistance during the processing process, in balance with the adhesive 42, and in addition to PET, PO and PVC may also be used. We are getting good results.

Next, as shown in FIG. 7, the sensor chip 4 is attached to the adhesive 41.
An adhesive 31 is put between the sensor chip 4 and the printed circuit board 1, which are pasted together with one side of the printed circuit board 1 as a reference, and fixed.

This adhesive should be elastic or rubber-like.
In addition, since the thermal expansion coefficients of the sensor chip 4 and the printed circuit board l are significantly different, it is necessary to consider the relationship between the elastic modulus, elongation strength, and adhesive thickness of the adhesive 31 in order to sufficiently alleviate thermal stress. If the elastic modulus is large, the strain on the printed circuit board 1 side will greatly affect the sensor chip, so the adhesive thickness should be relatively large. In the present invention, a silicon-based resin that does not lose its elasticity even at low temperatures is used. . In the present invention, a heat-addition reaction type silicone resin is used and has a great effect in alleviating stress, particularly in alleviating thermal reactions at low temperatures of about -60°C.

Thereafter, using a well-known bolter, the bonding pads 6 of the sensor chip 41 and the bonding pads 7 and 9 on the printed wiring board 1 side are electrically connected with wires 8. Materials used (e.g.

Due to constraints such as heat resistance of the film 41 with adhesive 42, etc., bonding with aluminum wire was performed.

The aluminum wire used was Al-3i (1%) φ35.

Next, as shown in FIG. 9, it is necessary to use a liquid molding agent with high thixotropic properties in this mold to which the mold 10 is applied, as can be seen from the cross-sectional shape shown in FIG. In the present invention, a material having a relaxing effect and sufficient stress relaxation even in a low temperature range is required. In the present invention, a material having a relaxation effect is required.

As a result of various studies, it was found that an St-based molding agent, which has relatively weak adhesive strength but can relax stress over a wide range of temperatures, is preferable. Based on this result, KJR-9050 manufactured by Shin-Etsu Chemical Co., Ltd. was used as the sample in the present invention, and very good results were obtained. However, this 9050 has a high thixotropic property, so even if air bubbles are trapped during molding, the air bubbles will not come out and will solidify. In this state, there will be a major problem with long-term reliability. Put away, especially in hot water (60°C-90%R)1
Operation tests at temperatures such as 85° C. and 85% RH are fatal. The presence of air bubbles on the active surface of the sensor chip 4 is indeed fatal. To solve this problem,
As a result of various experiments such as heating, good results could be obtained by foaming for 2 to 3 minutes under vacuum.

Finally, the film 41 with the adhesive 42 attached.

By peeling it off together with the adhesive 42, the product of the present invention shown in Figure ff11 is completed.

In the present invention, the adhesive 42 is irradiated with ultraviolet rays to lower its adhesive strength and to make it easier to peel off. Specifically, Niretsubu Holder (trade name) manufactured by Nitto Denko was used, and among them, UE-8 was used, and good results were obtained. Afterwards, we investigated an improved type of Niretsubu holder and obtained even better results. The optimal ultraviolet irradiation condition at this time is about 300 mJ/cni. However, it has been found through experiments in the present invention that good results can be obtained if it is 200 mJ/Cn1 or more.

[Effect of yA light] In the present invention, compared to the top method, in the top method, light (hu) enters from the direction shown in the t52 diagram. ) is not optically flat, the light receiving element 9
A clear image is not formed on the surface of the molding agent 10 due to the low light transmittance of the molding agent 10, and also due to the inclusion of air bubbles and foreign matter during the molding process.

The sensitivity of the sensor 9 will decrease, and if we include the surface of the molding agent, interface reflection, etc., the amount of light that enters directly will be approximately 80
%. Figure 10 shows the transmittance of the molding agent used for the top type. From Figure 10, when a light resistance test was conducted,
It can be seen that the transmittance decreases. In addition, the spectral sensitivity characteristics of the sensor (
From FIG. 11), the transmittance of the molding agent at a wavelength of 600 nm is about 87% (0.1 mm thickness), considering the thickness, etc.

It is expected that the amount of incident light will drop to about 80% by the time it reaches the sensor. Furthermore, when light enters the molding agent, the interface reflection at the interface with the air layer is around 105 (this is a value related to the refractive index of the molding agent), and the effective light amount is 0.9XO ,8=0.72
This results in a drop to around 70%.

In contrast, in the method of the present invention, there is no obstacle such as a molding agent and the light enters directly through the glass 4 of the sensor chip, so the transmittance of the chip glass 4 and the interface reflection between the chip glass 4 and the air layer are It is decided by the relationship only. The transmittance of the chip glass 4 is 98% or more in a wavelength range of 300 nm or more, and since the refractive index of the chip lath 4 is about 1°47, the interface reflection is about 10%. Therefore, the effective light amount is 0.98xO, 9 = 0.9, which is just under 90%, which means that the amount of light is 0.97 compared to the top method.
0.72=1.25 times, which is a 25% advantage.

Other disadvantages of the top method include the fact that the surface of the molding agent must be optically flat1.
The effects of the present invention are immeasurable.

Compared to the bottom method, there is a problem with the connector in the bottom method, and the circuit block A cannot be electrically connected to the glass substrate 21 unless the connector 24 is always pressed into contact with the glass substrate 21. Therefore, when assembled as a sensor unit, It was necessary to always consider the pressure welding structure.

On the other hand, in the present invention, the sensor chip 4 and
Since the circuit board 1 is directly connected with the well-known wire bond, there is no need to always consider the pressure welding structure when designing the unit, which has great design merits. Compared to the bottom method, which uses only bonding points, the present invention has far superior reliability.

In the case of light incidence, in the bottom method, the glass substrate 21
Since it enters from the side, the surface of the glass substrate, the transmittance of the glass substrate 21, the interface between the glass substrate 21 and the die attach 22, the transmittance of the die attach 22, the interface between the die attach 22 and the sensor chip glass 4, and the sensor chip glass 4 There is attenuation of light depending on the transmittance. This attenuation amount is 0.9 (interface reflection of glass substrate 21) xo, 99 (transmittance of glass substrate 21) xo, 9B (glass substrate 21 and die attach 2
2 interface reflection) Xo, 85 (Transmittance of die attach 22 (value after light resistance)) xo, 98 (interface reflection between die attach 22 and sensor chip glass) xo.

99 (transmittance of sensor chip glass) = 0.72, compared with 0.9 (interface reflection and transmittance of sensor chip glass, 0.9XO, 99 = 0°89) of the structure of the present invention. There is a big difference. Compared to the bottom method, the present invention has a light amount advantage of 0.970.72=1.25, which is 25%.

Furthermore, since the present invention does not pass any organic material in the incident optical path, there is very little change in transmittance over time, making it possible to maintain stable sensor characteristics. p! Figure S10 shows the transmittance characteristics of a 0.1 mm thick organic material before and after the optical test. This resin was applied as a molding agent and a die attach agent in the present invention.

In addition, since no glass substrate is used, there are immeasurable benefits such as weight reduction and space saving.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing a cross section of a contact type image sensor module according to the present invention. FIG. 2 is a diagram schematically showing a cross section of a top type contact type image sensor module. FIG. 3 is a diagram schematically showing a cross section of an image sensor module with close contact in the bottom method. 4 to 9 are diagrams showing the procedure for producing a contact type image sensor module according to the present invention. FIG. 1O is a diagram showing typical wavelength characteristics of light transmittance of the molding agent 10 and die attach 22 used in the present invention. FIG. 11 is a diagram showing the relative spectral sensitivity characteristics of the sensor used in the present invention. l... Printed circuit board 2... Electronic component 3... Solder 4... Sensor chip (sensor chip glass) 5. Die attach agent 6... Bonding area (chip side) (bat) 7.9. Bonding area (printed circuit board side) (butt) 811. Bonding wire 9... Elements 10 such as light receiving elements, Molding agent 11... Mold frame 12, Adhesive 21, Glass substrate 22... Optical die attach agent 23,... Rubber frame 24・1. Connector A...Circuit block 31... Adhesive material 41... Film 42... Adhesive or more v Figure 1 Figure Z ≠ Figure ξ Figure 41 Figure 2 Figure 1 θ Figure Relative -& nm) Divided A/IL 1st/Fig.

Claims (1)

[Claims] In the module structure of the contact image sensor, the sensor chip is mounted on the circuit board by bonding the sensor chip to the side surface of the circuit board that drives the sensor chip and processes signals from the sensor chip. Modular structure of contact type image sensor.