JP2918423B2 - Imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image device such as an LED head, a contact type image sensor, and a liquid crystal shutter array head, and more particularly to a flip-chip connection type image device.

[0002]

2. Description of the Related Art In image devices such as LED heads, it has been proposed to connect a light receiving / emitting array to a substrate by flip-chip bonding (for example, Japanese Utility Model Application Laid-Open No. 63-180,249). The advantage of flip-chip connection is that many connections can be made at high speed. However, the flip-chip connection has the following problems, and no prior art mentioning this point has been found. 1) When connecting, the patterns of the bumps and light receiving and emitting elements of the light receiving and emitting array are not visible, so the mounting is done by looking at the back of the array. 2) In flip-chip connection, the array is connected while applying pressure, but the pressure may not be applied uniformly and the array may be destroyed.

To explain point 1) above, in the conventional example, the array is conveyed by a collet or the like while looking at the back of the array, and positioning is performed by looking at a marker on the substrate. The mounted array can only be seen from the back, and the pattern of the mounted array cannot be used for positioning the next array. By the way, what can be seen from the back of the array is a line when the array is cut out from the wafer, and has no direct relation to the pattern of the light receiving / emitting body. There is an error of only the dicing accuracy between the line at the time of dicing (the shape of the back surface of the array) and the pattern of the light receiving / emitting body, which reaches about ± 100 μm. The mounting accuracy of the light receiving / emitting array must be much higher than this. Therefore, if the mounting is performed using the outer shape of the array, the mounting accuracy of the array which is crucial in the image apparatus cannot be obtained.

[0004] Explaining the above point 2), for example, gold bumps are formed on an array, and solder bumps are formed on a substrate, for example. After temporary fixing, flip-chip connection is completed in a reflow furnace or the like. Here, it is necessary to apply considerable pressure to the array, which can be, for example, on the order of a few kg per array. A large number of arrays are mounted on the board,
Pressurization is applied to all arrays simultaneously as it passes through the reflow oven. It is difficult to uniformly apply pressure to all the arrays, and if the pressure varies, the fragile light receiving / emitting array such as GaAs is damaged.

[0005]

SUMMARY OF THE INVENTION The first and second aspects of the present invention have the following objects in a flip-chip connection type image device. 1) It is possible to mount on the substrate while observing the pattern of the light receiving and emitting array, and to improve the mounting accuracy of the array. 2) When connecting the flip chip, all the light emitting and receiving arrays can be pressed evenly to prevent the array from being damaged. 3) High surface flatness, low deformation such as warpage, and low temperature deformation.

An object of the present invention is to achieve the above object while minimizing the cost of the substrate.

[0007]

An image apparatus according to the present invention comprises a high rigidity first substrate provided with a common electrode wiring on an upper surface and a low rigidity second substrate provided with a data bus on a lower surface. Individual electrodes, sandwiching a light receiving and emitting array having a common electrode on the lower surface,
A common electrode of the array is connected to a common electrode wiring of a first substrate, and individual electrodes of the array are flip-chip connected to a data bus of a second substrate. A light-transmitting hole is formed at a position facing the light receiving / emitting section. Preferably, the material of the high rigidity substrate is glass or ceramic, and the material of the low rigidity substrate is plastic. As the light receiving / emitting array, for example, an LED array, a liquid crystal shutter array, a PLZT array, a CCD array, or the like is used. Further, as the high rigidity substrate, for example, a glass substrate, a ceramic substrate, a crystallized glass substrate, or the like is used, and these materials are glass or ceramic. For the high-rigidity substrate, use a substrate whose thermal expansion coefficient is close to that of the light emitting and receiving array or whose thermal expansion coefficient is close to 0. A glass substrate is used. As the low-rigidity board, for example, a flexible printed board, a transparent plastic board, a hard printed board, or the like is used.

[0008]

According to the image apparatus of the present invention, at least two
The light receiving / emitting array is sandwiched between two substrates, the array is mounted on the first substrate having high rigidity, and then flip-chip connected to the second substrate having low rigidity. High rigid first
In mounting on a substrate, an array arranged so that the pattern side (front of the array) of the light receiving / emitting body can be seen is transported and mounted by a collet or the like. When picking up with a collet, the pattern of the array can be seen, and the first
The mounting position on the substrate is determined. A marker for a mounting position is provided on the substrate, and the marker is used as a clue or a pattern of an already mounted array is mounted as a clue. In this way, the array can be mounted precisely on the first substrate having high rigidity based on the actual pattern of the array, regardless of the external dimensions of the array. Next, flip-chip connection is made to the second substrate having low rigidity. The positioning of the array has been completed when the first substrate is mounted, and there is no longer any problem of misalignment. When the array is pressed during flip-chip connection, the array is sandwiched between the first substrate and the second substrate, so that all the arrays can be uniformly pressed. As a result,
Array damage due to local pressure is eliminated. An optical path to the light receiving and emitting element is secured by a light transmitting hole, and a difference in thermal expansion coefficient between the first substrate and the second substrate can be absorbed by the light transmitting hole.

It is useless to use high-precision, high-rigidity substrates for all two substrates. In addition, a high-precision substrate, for example, a glass substrate or a ceramic substrate has high rigidity, and if two substrates are both high-precision substrates, the substrate cannot be deformed to absorb a force, and an external force or a thermal stress causes an array or a flip chip. It is not preferable because it concentrates on the connection part. Therefore, the first substrate is a high-rigidity substrate, and the second substrate is a low-rigidity substrate.
The low-rigidity second substrate is deformed according to the high-rigidity first substrate, and if the high-rigidity first substrate achieves positional accuracy, the low-rigidity second substrate follows. Therefore, utilizing the surface flatness and the small warpage of the high-rigidity first substrate, the low-rigidity second substrate is deformed accordingly. If the coefficient of thermal expansion of the first substrate having high rigidity is close to that of the light emitting / receiving array, the second substrate having low rigidity is also thermally deformed accordingly. Further, even if there is a temperature change, the image device only deforms with the same expansion coefficient as a whole. Here, depending on the use of the image apparatus, for example, when two sets of images are used to synthesize two sets of images to obtain a final image, it is required that the temperature deformation is literally small. In such a case, it is preferable that the coefficient of thermal expansion of the first substrate having high rigidity be literally approached to zero.

[0010]

1 to 5 show a first embodiment. FIG. 1 shows a cross section of a main part of the image device after flip-chip connection. In the drawing, reference numeral 2 denotes a first substrate, which uses a glass substrate, a ceramic substrate, a crystallized glass substrate, or the like, and all of these materials are ceramic. Or glass. Each of these substrates has high rigidity, small warpage, and a small coefficient of thermal expansion as compared with a plastic substrate or the like. Reference numeral 4 denotes a second substrate, which uses a substrate having low rigidity, such as a flexible printed substrate, a transparent plastic substrate, or a hard printed substrate. Reference numeral 6 denotes an LED array, which is sandwiched between the substrates 2 and 4 and mounted in a straight line, and the common electrode side is connected to the first substrate 2.
Next, the individual electrode side is connected to the second substrate 4. Reference numeral 8 denotes a common electrode wiring provided on the first substrate 2, reference numeral 10 denotes a conductive adhesive such as silver paste, and reference numeral 12 denotes a common electrode of the LED array 6. Reference numeral 14 denotes gold bumps provided on the individual electrodes of the LED array 6, and 16 denotes solder bumps provided on the second substrate 4. Then, the gold bumps 14 and the solder bumps 16 are flip-chip connected. In addition, a solder bump is provided on the LED array 6 side,
A gold bump may be provided on the substrate 4 side.

FIG. 2 shows an LED array 6 on the first substrate 2.
This shows the mounting process. The first substrate 2 does not require precision wiring, and is provided with a common electrode wiring 8 and a substrate marker 18 for positioning the mounting position of the LED array 6. Next, a conductive adhesive 10 is applied to a portion where the array 6 is mounted. Reference numerals 20 and 20 denote chip markers provided on the LED array 6, which are formed simultaneously with the individual electrodes connected to the light emitting body 22, and have a constant positional relationship with the individual electrodes. The LED array 6 after dicing is housed in a tray or the like with the light emitting body 22 side facing up, picked up one by one by a collet or the like, and mounted on the substrate 2.

In the first mounting of the LED array 6, the mounting position is determined so that the chip marker 20 appears at a correct position with respect to the substrate marker 18. In mounting the second and subsequent LED arrays 6, the mounting position of the next array 6 is determined using the chip marker 20 of the previously mounted LED array 6 as a clue. Here, the mounting position is determined so that the chip marker 20 of the next array 6 appears at a predetermined position with respect to the chip marker 20 of the previous array 6, and the board marker 18
Is used to confirm the mounting position and to prevent errors in the mounting position from accumulating.

FIG. 3 shows the second substrate 4 before flip-chip connection. Data buses 24 and 26 are vacuum-deposited Al
Wiring or copper wiring by etching is used. Reference numeral 28 denotes a row of the solder bumps 16, where the gold bumps 1 of the LED array 6 are arranged.
4 and flip-chip connection. The data buses 24 and 26 are folded wiring, and the data bus 24 is connected to the individual electrodes of the LED array 6, and the individual electrodes of the LED array 6 are connected to the data bus 26.

FIG. 4 shows the LED array 6 used in the embodiment. Reference numeral 20 denotes the chip marker, reference numeral 22 denotes a light emitting body, and approximately 64 dots are provided for each array 6, and reference numeral 14 denotes the gold bump.
4-1 and gold bumps 14-1 on the individual electrodes of the array.
And the gold bump 14-2, and the lower gold bump 14-
2 to the data bus 26. Thus, the luminous body 22
By providing two gold bumps 14, 14 for each one and performing flip chip connection at two locations, the data bus 24,
26 is connected.

FIG. 5 shows a process of assembling the LED head of the embodiment. There is a position variation of about ± 100 μm between the outer shape line of the LED array 6 and the actual pattern. This is because the outer shape of the array 6 is determined by dicing and is not particularly related to the pattern. In flip-chip connection, it is necessary to mount the LED array 6 with an error of, for example, ± 10 μm or less with respect to the actual pattern. If this condition cannot be satisfied, the intervals between the light-emitting members 22, 22 change at the transition between the arrays 6, 6, and white streaks, black streaks, and the like are generated. In the embodiment, when the LED array 6 is picked up by the collet, the chip marker 20 is pattern-recognized. For the substrate 2, the substrate marker 18 or the chip marker 20 of the already mounted LED array 6 is used. The mounting position of the next LED array 6 is determined. In this way, the mounting position is determined based on the actual pattern of the LED array 6, for example, ± 1.
The LED array 6 can be mounted with an error of 0 μm or less. Assuming that 40 LED arrays 6 are mounted on the substrate 2,
The step of mounting the next array 6 is repeated by looking at the chip markers 20 of the previous array 6, and the position of the chip marker 20 with respect to the last substrate marker 18 is confirmed after the mounting of 40 arrays. If the mounting is correct and there is no accumulated mounting error, the substrate marker 18 should appear at a predetermined position with respect to the chip marker 20.

Next, the second substrate 4 provided with the solder bumps 16 in advance is temporarily fixed to the first substrate 2. At this time, the bump 16 and the bump 14 are temporarily fixed by the flux of the solder bump 16. The second substrate 4 is a transparent substrate, and the alignment is performed so that the solder bumps 16 overlap the gold bumps 14 or the markers provided on the second substrate 4 overlap the substrate markers 18 and the like. In this state, the LED array 6 is sandwiched between the first substrate 2 and the second substrate 4, and when a pressure is applied between the substrates 2 and 4, this force is applied to the LED array 6. This force is necessary for temporary fixing by flip-chip connection, and is set to, for example, about several kg per LED array 6. Since the LED array 6 is sandwiched between the two substrates 2 and 4, substantially uniform pressure is applied to the 40 LED arrays 6, so that the pressure is locally concentrated and the LED array 6 is not damaged. In this state, if the LED array 6 sandwiched between the substrates 2 and 4 is passed through a reflow furnace or the like, flip-chip connection by soldering is completed.

In the embodiment, the first substrate 2 is a substrate having high rigidity and a low coefficient of thermal expansion, and the second substrate 4 is a substrate having low rigidity. It is wasteful and dangerous to use both of the substrates 2 and 4 as rigid substrates. For example, when a force is applied between the substrates 2 and 4 when sandwiching them, if the two substrates are made of a highly rigid substrate, there is no escape for the force, and the flip chip connection portion and the LED array 6 will be damaged. . On the other hand, if the second substrate 4 is a low-rigid substrate, the force is absorbed by the deformation of the substrate 4 and the damage to the LED array 6 and the like can be prevented. Next, the first substrate 2 is a substrate such as glass, ceramic or crystallized glass which has a small warpage and high surface accuracy. The second substrate 4 is a substrate having low rigidity and originally having a large warp or the like and a low accuracy. The accuracy of the second substrate 4 can be improved.

A material such as glass, ceramic, or crystallized glass has a smaller coefficient of thermal expansion than the plastic material of the second substrate 4 and is close to the coefficient of thermal expansion of the LED array 6. As a result, the relative temperature deformation between the LED array 6 and the first substrate 2 is small, and the second substrate 4 is low in rigidity, so that the temperature is deformed according to the first substrate 2 and the thermal stress and the like are reduced. . This means that even if the ambient temperature changes, the distance between the LED arrays 6 and 6 does not change, and the position of the solder bump 16 with respect to the gold bump 14 does not change.

In some applications, the coefficient of thermal expansion of the LED head must be literally zero. In such a case, if the first substrate 2 is made of SiO2-TiO2 glass such as 93% by weight of SiO2 and 7% by weight of TiO2,
Can have a coefficient of thermal expansion of substantially zero.

In the embodiment, the board markers 18 are provided for each of the LED arrays 6. However, the board markers 18 may be provided only at two positions on both ends of the board 2. The second substrate 4 is 1
Although the data buses 24 and 26 are folded wirings as layer wirings, multilayer wirings may be used, and other wirings may be used.

[0021]

Embodiment 2 FIG. 6 shows a second embodiment. In the figure, 30 is a rigid printed board used as a second board,
Reference numeral 32 denotes a through hole for transmitting light from the LED array 6. Although the transparent substrate is used as the second substrate 4 in the embodiment shown in FIGS. 1 to 5, the second substrate can be constituted by an inexpensive hard printed circuit board 30. In other respects, it is similar to the embodiment of FIGS.

[0022]

According to the first and second aspects of the present invention, the following effects can be obtained. 1) It can be mounted on the substrate while observing the pattern of the light receiving and emitting array, and the mounting accuracy of the array is improved. 2) The light emitting / receiving array can be uniformly pressed when flip-chip connected, preventing the array from being damaged. 3) The surface flatness of the substrate can be increased, the deformation such as warpage can be reduced, and the temperature deformation can be reduced while minimizing the cost of the substrate.

According to the second aspect of the present invention, since the material of the second substrate having low rigidity is made of plastic, the light transmitting holes can be easily formed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part in a longitudinal direction of an image apparatus according to an embodiment.

FIG. 2 is a plan view of a main part of a first substrate in the image apparatus according to the embodiment.

FIG. 3 is a plan view of a second substrate in the image device according to the embodiment.

FIG. 4 is a plan view of an LED array used in the embodiment.

FIG. 5 is a flowchart showing an assembling process of the image apparatus according to the embodiment;

FIG. 6 is a cross-sectional view in the short direction of the image apparatus according to the second embodiment.

[Explanation of symbols]

 2 First substrate 4 Second substrate 6 LED array 8 Common electrode wiring 10 Conductive adhesive 12 Gold plating film 14 Gold bump 16 Solder bump 18 Board marker 20 Chip marker 22 Light emitter 24, 26 Data bus 28 Row of solder bump 30 rigid printed circuit board 32 through hole

Continued on the front page (51) Int.Cl. ⁶ identification code FI H01L 33/00 (58) Fields investigated (Int.Cl. ⁶ , DB name) B41J 2/44 B41J 2/45 B41J 2/455 H01L 21 / 60 311 H01L 31/02 H01L 33/00

Claims (2)

(57) [Claims] 1. An individual electrode on an upper surface and a common electrode on a lower surface between a high-rigidity first substrate provided with a common electrode wiring on an upper surface and a low-rigidity second substrate provided with a data bus on a lower surface. Sandwiching a light emitting and receiving array having electrodes, connecting the common electrodes of the array to the common electrode wiring of the first substrate, and flip chip connecting the individual electrodes of the array to the data bus of the second substrate; An image device, wherein a light-transmitting hole is formed in the second substrate at a position facing a light-receiving / emitting portion of the light-receiving / emitting array. 2. The image apparatus according to claim 1, wherein the material of the high-rigidity substrate is glass or ceramic, and the material of the low-rigidity substrate is plastic.