JP2749357B2 - How to mount a multi-chip image sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mounting method of a multi-chip image sensor used for a 1: 1 contact image scanner or the like.

2. Description of the Related Art In recent years, in image scanners and the like, in order to reduce the size of an optical system, development of a unit-size close-contact type image sensor in which the sensor itself is configured in a unit size has been activated. In this case, for example, when an IC image sensor chip using a Si wafer is used, the length is limited by the size of the Si wafer. It is necessary to arrange the sensor chips on the same substrate. Such a multi-chip type is known, for example, as “CCD contact image sensor” of “ICS87-55” in the TV Society.

As such a multi-chip image sensor,
For example, a plurality of silicon IC image sensor chips each having a light receiving pixel portion formed with the same pitch are arranged in a straight line.

Such a plurality of IC image sensor chips are fixed by, for example, die bonding on the same alumina substrate. As such a die bonding method, there are the following various methods.

Here, regarding the features of the various methods, ... joining materials, ...
Metallization on the back of the die, working temperature, working atmosphere, ohmic properties, heat dissipation, wire bonding adaptability, furnace seal adaptability, mass productivity, and cost.

a. Eutectic bonding method Au-Si, Au-Ge or Au-Sn, unnecessary or Au deposition, 320-450 ° C, inert atmosphere or reducing atmosphere, good, good, suitable, suitable, good, high b. Solder bonding Legal Pb-based solder or Sn-based solder, Ni, Ni-Au or Cr-Ni-Au, etc., 250-350 ° C, inert atmosphere or reducing atmosphere, good, good, unsuitable only for thermocompression bonding, suitable, good, medium c .Resin bonding method Ag + Epoxy, Ag + Polyimide or Ag + Silicon, Not required, Room temperature (Curing at 150-200 ℃), Air or inert atmosphere, Instable, Poor, Suitable, Suitable for polyimide only, Excellent, Low d. law PbO-B ₂ O ₂ -based glass, unwanted, four hundred and twenty to six hundred ° C., air defect, defective, suitable, proper, rather poor, in such die-bonding method is required a working temperature of both the high temperature, the resin of the c At present, compared to other die bonding methods (eutectic bonding method, solder bonding method, glass bonding method), Of reliability, workability, is excellent in mass production, and the like.

In this resin bonding method, a thermosetting die bonding adhesive is applied on a substrate at room temperature by a dispensing method, a stamping method, a screen printing method, or the like in an amount equivalent to a chip width.
Apply with a thickness of about μm, press and arrange each chip on it while aligning them, and then cure in a batch process in an oven at a heating temperature of 120 ° C to 250 ° C for 1 to 2 hours (curing) ).

Here, examples of the conductive die bonding adhesive include the following product names. Here, regarding the properties of the adhesive of each product name, ... properties (mixing ratio), presence or absence of solvent, ... composition (filler / resin), ... cure conditions (temperature / time), ... volume resistivity (Ωcm) ), Thermal conductivity (cal / cm-sec.)
° C.), ... extracted impurities (Cl ^- | shall indicate in the order of Na ^+). , A. Chemitite CT212 (manufactured by Toshiba Chemical Co., Ltd.) One-part, yes, Ag / epoxy, 200 ° C / 1 hr, 0.6 × 10 ^-4 , 6 × 10 ^-3 , 5 | 5 B.EN-4000 (Hitachi Chemical Co., Ltd.) One-part, yes, Ag / epoxy, 175 ° C / 1hr, 2 × 10 ^-4 , 6 × 10 ^-3 , 10 | 10 C.EN-4007X-13 (manufactured by Hitachi Chemical) One-part, no , Ag / epoxy, 150 ° C / 1hr-250 ° C / 40sec, 3.3 × 10 ^-4 ,-, 10 | 10 D.CRM-1038 (manufactured by Sumitomo Bakelite Co., Ltd.) One-part, none, Ag / epoxy, 200 ° C / 1hr ~ 170 ℃ / 20sec ＋ 350 ℃ / 20sec, 2 × 1
0 ^-4 , 3 × 10 ^-3 , 10 | 10 E.CRM-1058 (manufactured by Sumitomo Bakelite Co., Ltd.) One-part, yes, Ag / polyimide, 150 ° C / 1hr-250 ° C / 1hr, 2 × 10 ^-4 -, 10 | 20 F. Ablebond 84-1 LMI (Ablestic) One-part, None, Ag / Epoxy, 150 ° C / 1hr, 2 × 10 ^-4 , 4.5 × 10 ^-3 , 10 | 10 G. Ablebond 71-1 LMI (manufactured by Ablestic) One-part, yes, Ag / polyimide, 150 ° C / 30min-275 ° C / 30min, 2 × 10 ^-4 ,-, 10 | 5 H.EPO-TEK H-20ELC (Epoxy Technology) Two-part (1: 1), None, Ag / Epoxy, 120 ° C / 15min, 3 × 10 ^-4 , 4 × 10 ^-3 , 30 |-I.EPO-TEK H35-175M (Epoxy Technology One-part, None, Ag / Epoxy, 180 ° C / 1hr, 2 × 10 ^-4 ,-, 10 | 10 J. Du Pont 4621D (Du Pont) One-part, Yes, Ag / Epoxy, 175 ° C / 1hr, 4 × 10 ^-4 ,-, 20 | 10 KC-990 (manufactured by Amicon) One-part, none, Ag / Epoxy, 155 ° C / 1hr, 6.5 × 10 ^-4 ,-, 10 | 5 LC-940-AXLC (manufactured by Amicon) One-part, yes, Ag / polyimide, 175 ° C./30 min to 275 ° C./30 min, −, −, 10 | 20 Problems to be Solved by the Invention In such a multi-chip image sensor, the distance between the light receiving pixel portions even between each IC image sensor chip. Needs to be properly maintained so as to be equal to the interval between the light receiving pixel portions in the chip. If this interval is not properly maintained, the continuity of the light receiving pixel portion is disrupted, and the reading quality is degraded.

However, in the case of a conventional mounting method using a die bonding adhesive, as described in the section of “4.2 Die bonding” in the above-mentioned document, chip displacement occurs at the time of curing each chip, Pixel pitch between adjacent chips fluctuates. As a result, the reading quality is deteriorated as described above. Such a chip shift at the time of die bonding is 100 ° C. regardless of the curing temperature (curing temperature) of the die bonding adhesive described above.
° C or higher, the thermal expansion coefficient of the sensor chip due to Si α _Si {3.5 × 10 ^-6 [1 / ° C] and the thermal expansion coefficient of the substrate due to alumina Al ₂ O ₃ α _B = α (Al ₂ O ₃ )} Since there is a difference between 6.5 × 10 ^-6 [1 / ° C], the substrate and each sensor chip are fixed at the time of expansion due to the temperature at the time of curing (the amount of expansion is substrate> sensor chip). Therefore, at normal temperature, which is the original use condition, α
Since (Al ₂ O ₃ )> α _Si , the dimensions of the image sensor are compressed and shorter than those at the time of chip manufacture. For this reason, when viewed as a whole, each sensor chip becomes shorter, and the pixel interval at the junction between each chip becomes wider (the pixel interval within each chip becomes shorter). Has occurred. In particular, since the chip of the same-size contact image sensor is elongated, a dimensional deviation due to a difference in the coefficient of thermal expansion between the substrate and the chip appears remarkably. In the case of the same-size contact color sensor, a color tone shift occurs at a joint portion of each sensor chip, resulting in remarkable image deterioration.

Incidentally, even in the above-mentioned literature which finds the optimum conditions for the adhesive and the adhesive curing temperature, as shown in FIG. 9, an alignment error of about ± 15 μm occurs,
For example, it is insufficient to meet the specifications of a 400 dpi high-density sensor for A3 size.

In addition, the heat-curable one-component epoxy adhesive has a thixotropy property in which the viscosity decreases during a temperature rise to heat-curing, and displacement occurs even when the applied adhesive flows on a chip.

Here, the configuration of the conventional multi-chip type image sensor and the point where the pixel arrangement density is deteriorated at the junction between the chips will be discussed in detail with reference to FIG. First, this image sensor is printed on a substrate 1 on which a circuit pattern is printed.
A plurality of CCDs I by die bonding adhesive 2
The C image sensor chips 3a, 3b, and 3c are bonded and fixed in a state where they are arranged adjacent to each other, and a sealing glass (window glass) 6 is fixedly mounted on the substrate 1 via a spacer 4 and a sealing glass 5.

Here, the substrate 1 is an alumina substrate, and the IC image sensor chip 2 is made of silicon.

The characteristics of alumina in this case are as follows: Main component: Al ₂ O ₃ = 92 to 94%, SiO ₂ , MgO, etc. Resistance: 10 ¹² [Ω · cm], Coefficient of thermal expansion (0 to 100 ° C.) 6.0-6.5 × 10
^-6 [° C ^-1 ], Thermal conductivity: 0.03 to 0.04 [cal / cm · s · ° C], Dielectric constant (1 MHz): 8.5 to 9.5, Dielectric loss tangent (1 MHz): 0.001, Heat resistant temperature: 1000 [° C] Above, longitudinal elastic modulus: 3.7 to 4.1 × 10 ⁴ [kg / mm ² ], bending strength (tensile strength): 30 to 35 [kg / mm ² ], alpha ray generation rate: 0.03 to 0.5 [pieces / hour] Cm ² ].

The characteristics of silicon are as follows: main component: Si resistance: 2.3 × 10 ⁴ [Ω · cm]; coefficient of thermal expansion (0 to 100 ° C.): 3.5 × 10 ^-6 [° C. ^-1 ]; thermal conductivity: 0.2 ~ 0.35 [cal / cm · s · ° C], Dielectric constant (1MHz)… 12, Dielectric loss tangent (1MHz)… None, Heat resistant temperature… 1414 [° C], Longitudinal elastic modulus… C ₁ 1.7, C ₁₂ 0.7, C ₁₄ 0.8, × 10 ⁴ (kg / m
m ² ], bending strength (tensile strength): 30 [kg / mm ² ] / 10 min, alpha ray generation rate: 0.01 [pieces / hour · cm ² ].

Further, as the die bonding adhesive 6, among the various adhesives A to L described above, H EPO-TEK H-20EL is used.
Cure temperature Tc = 120 using C (Epoxy Technology)
Cure at ℃.

In addition, the ambient temperature Ta at the time of chip manufacture (particularly, at the time of mask alignment exposure) and at the time of use of the image sensor 1 is set to a normal temperature Ta
20 ° C.

Under such conditions, the length of the alumina substrate 1 is l
(Al ₂ O ₃ ), length of silicon chip 3 (effective chip length)
The l _Si, the thermal expansion coefficient of the alumina substrate _{1 α (Al 2 O 3)} , when the thermal expansion coefficient of the silicon chip 3 and alpha _Si, differential expansion in Cure temperature Tc (size difference) .DELTA.l is, .DELTA.l = .DELTA.l _{(Al 2 O 3) -Δl Si} = (α (Al 2 O 3) -α Si) (Tc-Ta) l , and the respective chip 3 in this state is bonded onto the substrate 1 (curing). Therefore, at the use temperature Ta, both the alumina substrate 1 and the chip 3 contract as the temperature decreases from the cure temperature Tc. However, the difference in the coefficient of thermal expansion, that is, α
(Al ₂ O ₃ ) ≒ 6.5 × 10 ^-6 and α _Si ≒ 3.5 × 10 ^-6 ,
The contraction rate of the alumina substrate 1 becomes larger.

Here, the shrinking method is such that each chip 3 and the substrate 1 are bonded and fixed to each other, and a strain ε is generated so that the mutual force P of the chip 3 and the substrate 1 is balanced, so that the chip 3 and the substrate 1 are stabilized. . Here, assuming that the stress is σ, the longitudinal elastic modulus is E, and the cross-sectional area is A, the strain ε is expressed as ε = σ / Eσ = P / A. Therefore, the equilibrium condition is P = A (Al ₂ O ₃ ) · ε (Al ₂ O ₃ ) · E (Al ₂ O ₃ ) = A _Si · ε _Si · E _Si It is. For example, A _Si = 0.7 mm width x 0.5 mm thickness = 0.35 mm ² ,
A (Al ₂ O ₃ ) = width 20 mm × thickness 1.6 mm = 32 mm ² , E _Si ≒
1.7 × 10 ⁴ kg / mm ² , E (Al ₂ O ₃ ) ≒ 3.8 × 10 ⁴ kg / mm ² . Therefore, there is almost no distortion ε of the alumina substrate 1 due to the stress σ. That is, the alumina substrate 1 has a thermal expansion coefficient α (Al ₂ O ₃ )
As a result, the chip 3 is compressed by generating a strain corresponding to the difference α (Al ₂ O ₃ ) −α _Si in the coefficient of thermal expansion between the alumina substrate 1 and the chip 3. For example, when l = 61 mm, (Tc−Ta) = 10
At 0 ° C., the amount of strain δl of the chip is δl = l (Tc−Ta) (α (Al ₂ O ₃ ) −α _Si ) = 61 × (120−20) (6.5 × 10 ⁻⁶ −3.5 × 10 ^{−) 6} ) = 18.3 µm. This results in pixel displacement at the junction between chips in the conventional example.

Means for Solving the Problems In a mounting method of a multi-chip type image sensor in which a plurality of IC image sensor chips are arranged adjacent to and fixed on the same substrate by a die bonding adhesive, When the thermal expansion coefficient is α ₁ and the thermal expansion coefficient of the silicon sensor chip is α ₂ , the thermal expansion coefficient α ₃ satisfying the relationship of | α ₃ −α ₁ | <| α ₂ −α ₁ | The surface opposite to the substrate-side bonding surface of the sensor chip was bonded and fixed to the fixing glass with a room-temperature-curable adhesive having visible light transmittance in advance.

 Further, the fixed glass was also used as the sealing glass.

Operation According to the above-described examination results, the difference in the amount of elongation between the silicon sensor chip and the alumina substrate during curing results in a pixel position shift almost as it is. Focusing on this point,
Using a fixed glass whose thermal expansion coefficient is larger than that of the sensor chip and closer to the substrate, the sensor chip is fixed on the fixed glass in advance with a room-temperature-curable adhesive at room temperature, so that the amount of elongation of the sensor chip during curing Becomes closer to the amount of elongation of the substrate, and even if the temperature becomes room temperature after the curing process, the amount of pixel displacement is reduced. Further, since the adhesive is fixed to the fixed glass at room temperature in advance, chip flow due to the thixotropic property of the die bonding adhesive is also suppressed. At this time, the fixed glass can be used as it is as the sealing glass, and this can be achieved without increasing the number of parts.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. The basic structure itself conforms to the conventional system, and the same or corresponding parts as those shown in FIG. 5 are denoted by the same reference numerals. Even in the present embodiment, finally, a plurality of sensor chips 3a to 3c are disposed adjacent to each other on the substrate 1 by the die bonding adhesive 2 and are adhesively fixed. Thus, in this embodiment, a long fixed glass 7 having a new predetermined characteristic is provided similarly to the substrate 1, and a plurality of sensor chips 3 a to 3 c are mounted on the fixed glass 7 with high visible light transmittance. The adhesive is fixed at room temperature by using a room temperature curing adhesive, for example, an ultraviolet curing adhesive 8. Here, the bonding surface of the sensor chips 3a to 3c to the fixed glass 7 is opposite to the bonding surface to the substrate 1. FIG. 2 shows a state at the time of bonding at ordinary temperature by irradiation of ultraviolet rays. Next, the spacer 4 is bonded and fixed on the substrate 1 on which the die bonding adhesive 2 is applied with a sealing adhesive 5 made of a room-temperature curing adhesive. Then, a series of the sensor chips 3a to 3c previously arranged adjacent to and fixed on the fixing glass 7 as described above is turned over, and is positioned on the die bonding adhesive 2 and cured to perform the sensor processing. 3c is adhesively fixed on the substrate 1. Finally, as shown in FIG. 1, the sealing glass 6 is bonded and fixed.

Here, for example, soda glass (thickness 0.5 mm) is used as the fixed glass 7. The characteristics of the soda glass is the main component ... PbO60~70%, B ₂ O ₃ addition resistance ... 10 ¹¹ or more [Omega · cm], the coefficient of thermal expansion (0~100 ℃) ... 5.3 × 10 -6 [° C. ^{- 1} ], thermal conductivity: 0.001 to 0.003 [cal / cm · s · ° C], dielectric constant (1 MHz): 12, dielectric loss tangent (1 MHz): none, heat-resistant temperature: 300 [° C], longitudinal elastic coefficient: 0.7 × 10 ⁴ [kg / mm ² ], bending strength (tensile strength): 3 to 5 [kg / mm ² ] / 10 min, alpha ray generation rate: 2.7 to 4.0 [pieces / hour · cm ² ].

That is, the coefficient of thermal expansion α _SG of the fixed glass 7 and the coefficient of longitudinal elasticity E _SG are α _SG ≒ 5.3 × 10 ^-6 [° C. ^-1 ] E _SG ≒ 0.7 × 10 ⁴ [kg / mm ² ] When the amount of elongation during curing is obtained using this value (the other conditions are the same as those described above), ε _SG / ε _Si ≪1, and Δl _SG ≒ 1 (Tc−Ta) α _SG = 61 × (120−20) × 5.3 × 10 ⁻⁶ = 32 μm. At this time, the elongation amount of the alumina substrate 1 is as follows: Δl (Al ₂ O ₃ ) ≒ l (Tc−Ta) α (Al ₂ O ₃ ) = 61 × (120−20) × 6.5 × 10 ⁻⁶ = 40 μm .

Therefore, the difference in elongation between the fixed glass 7 and the substrate 1 is 8
μm and fixed.

Therefore, ε _SG / ε (Al ₂ O ₃ )> 1 holds, and even if the substrate 1 contracts at room temperature according to the thermal expansion coefficient, the pixel displacement at the connection between the chips becomes 8 μm or less, and the displacement is small. It will be. In addition, when each of the sensor chips 3a to 3c is die-bonded to the substrate 1 alone, warpage may occur. However, according to the present embodiment, the sensor chips 3a to 3c are bonded and fixed in advance to the fixed glass 7 having high flatness. No warpage occurs due to die bonding.

Also, instead of soda glass as the fixed glass 7,
A case in which sheet glasses of the same size are used will be described. The coefficient of thermal thermal expansion α _SH and the coefficient of longitudinal elasticity E _SH are α _SH ≒ 8.5 × 10 ^-6 [° C. ^-1 ] E _SH ≒ 0.7 × 10 ⁴ [kg / mm ² ], respectively. When the amount of elongation at the time of curing is obtained using (the other conditions are the same as those described above), ε _SH / ε _Si ≪1, and Δl _SH ≒ l (Tc−Ta) α _SH = 61 × (120−20) × 8.5 × 10 ⁻⁶ = 52 μm. At this time, the elongation amount of the alumina substrate 1 is the same as the above case, and Δl (Al ₂ O ₃ ) = 40 μm. Therefore, the difference in the amount of elongation between the fixed glass 7 and the substrate 1 is fixed at 12 μm. Therefore, ε _SH / ε (Al ₂ O ₃ )> 1. Even if the substrate 1 shrinks at room temperature in accordance with the thermal expansion coefficient, the pixel displacement at the connection between the chips becomes 12 μm or less, and the displacement is small. It will be.

If these conditions are collectively expressed, the fixed glass 7 satisfying the condition (A · E of sensor chip) <(A · E of fixed glass) may be used. That is, the thermal expansion coefficient of the alumina substrate 1 is α ₁ , and the silicon sensor chip 3 is
| Α ₃ −α ₁ | <| α ₂ − where α ₂ is the thermal expansion coefficient of
alpha ₁ | becomes relationship in which may be used stationary glass 7 having a thermal expansion coefficient alpha ₃ which satisfies.

Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, the fixed glass 7 is used as it is as the sealing glass.

According to the present embodiment, since the fixed glass and the sealing glass are not separately required, the number of components can be left as it is. Also,
In this embodiment, which transmits only the glass 7, light loss to the sensor chip 3 is smaller than in the case of transmitting the two glasses 7, 6 as in the above embodiment.

In these examples, the case of the die bonding method using the die bonding adhesive (conductive) 2 by the resin bonding method has been described. However, the non-conductive die bonding adhesive and the method other than the resin bonding method are used. The same applies to the case where a die bonding adhesive is used by a die bonding method. In this case, in the eutectic bonding method, the solder bonding method, or the glass bonding method, the solidification temperature of the adhesive used is equivalent to the curing temperature in the resin bonding method.

Effects of the Invention As described above, the present invention provides | α ₃ −α ₁ | <| α when the thermal expansion coefficient of an alumina substrate is α ₁ and the thermal expansion coefficient of a silicon sensor chip is α _{2. 2-.alpha. 1} | a fixed glass having a thermal expansion coefficient alpha ₃ satisfying the relationship: and the substrate-side bonding surface of the sensor chip is bonded and fixed by cold-setting adhesive having a pre-visible light-transmissive opposing surface Therefore, using a fixed glass whose coefficient of thermal expansion is larger than that of the sensor chip and close to the substrate, and fixing the sensor chip on the fixed glass in advance at room temperature with a room temperature curing adhesive, a cure type sensor Even if the chip elongation is close to the substrate elongation and the temperature becomes room temperature after the curing process, the amount of pixel misalignment can be reduced. adhesive The chip flow due to the thixotropic property can be suppressed, and the fixed glass can be used as it is as the sealing glass without increasing the number of components.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a first embodiment of the present invention, and FIG.
FIG. 3 is a sectional view showing a fixed state on a fixed glass, FIG. 3 is an exploded sectional view, FIG. 4 is a schematic sectional view showing a second embodiment of the present invention, and FIG. FIG. 1 ... substrate, 2 ... adhesive for die bonding, 3 ...
IC image sensor chip, 7: fixed glass, 8: cold-setting adhesive

Claims (2)

(57) [Claims] 1. A method of mounting a multi-chip image sensor in which a plurality of IC image sensor chips are arranged and fixed on the same substrate by using an adhesive for die bonding, and the thermal expansion of the alumina substrate is performed. When the coefficient is α ₁ and the thermal expansion coefficient of the silicon sensor chip is α ₂ , the fixed thermal expansion coefficient α ₃ satisfies the following relationship: | α ₃ −α ₁ | <| α ₂ −α ₁ | A method for mounting a multi-chip image sensor, wherein a surface opposite to a substrate-side bonding surface of the sensor chip is bonded and fixed to a glass in advance with a room-temperature-curable adhesive having visible light transmittance. 2. The method according to claim 1, wherein the fixed glass is also used as a sealing glass.