JPH06286220A - Manufacture of image forming device - Google Patents

Abstract

PURPOSE:To improve reliability of an LED head, by detecting a short circuit between electrodes of an LED array at a dynamic driving type LED head. CONSTITUTION:Output of an LED of an LED head is measured totally and a regular fall of output to be generated at a block cycle is detected. In dynamic driving, when a short circuit is in existence on one position, the short circuit is generated on the LED having the same dot number even if a block position is changed. Therefore, the short circuit can be detected through the regular fall of the output at the block cycle. When the regular fall of the output is detected, the LED where the fall of the output is most remarkable is decided to be the short circuit and inspection and repairing of the head are performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an image forming apparatus such as an LED head, a liquid crystal shutter head, an EL head, a PLZT optical head, a plasma head and a thermal head, and more particularly to a time division drive type image forming apparatus. Regarding detection of short circuits.

[0002]

2. Description of the Related Art There are two types of image forming apparatuses, a time-division drive (dynamic drive) type and a static drive type. In the time-division drive type image forming apparatus, a large number of image forming elements are divided into a plurality of blocks, and the image forming elements are time-division driven for each block. In the case of an LED head or the like, image forming elements are integrated in array units,
In many cases, time division drive is performed in array units. Therefore, the block that is a unit of a normal dynamic drive is an array unit. However, for example, two arrays may be dynamically driven as one block, or one array may be divided into two blocks and dynamically driven.

In the inspection of the image forming apparatus, it is necessary to inspect a short circuit in the board wiring, a short circuit between electrodes of the image forming element, and the like. However, as far as the inventor knows, there is no document that particularly refers to detection of a short circuit in an image forming apparatus. This is because the output variation of each image forming element is large, and the output variation due to a short circuit is hidden behind it, making it difficult to inspect. This is because, for example, in the case of an LED head, the output variation of each LED is large, and even if a short circuit occurs, it is difficult to detect the output variation due to the short circuit.
Therefore, in the inspection of the LED head of the conventional example, the allowable range of fluctuation of the light emission output of each LED is set to ± 10% or ± 20% with respect to the average light emission output of the LED of the entire head, and the allowable range is exceeded. It only checks the output fluctuation. In this case, a short circuit exceeding the above allowable width is only indirectly inspected.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which accurately detects a short circuit in the image forming apparatus and has no short circuit.

[0005]

According to the method of manufacturing an image forming apparatus of the present invention, a large number of image forming elements are arranged on a substrate, the image forming elements are divided into a plurality of blocks, and the image forming elements are arranged in each block. In a method of manufacturing an image forming apparatus configured to be dividedly driven, a step of inspecting an output of the image forming element, a step of detecting a regular output fluctuation occurring in a block cycle from the inspected output, and a step of Detecting a short circuit from a regular output fluctuation. The target image forming apparatus may be of a time-division drive type, and may be, for example, a thermal head, a liquid crystal shutter head, a PLZT optical head, an EL head, a plasma head or the like in addition to the LED head shown in the embodiments. INDUSTRIAL APPLICABILITY The present invention is suitable for detecting a short circuit without being disturbed by output fluctuations of individual image forming elements, and LE having large output fluctuations.
It is particularly suitable for detecting short circuits in the D head.

[0006]

According to the present invention, the output of the image forming apparatus is inspected, and the short circuit is detected from the regular output fluctuation repeated in block units. In the case of time division driving, if there is a short circuit at one location, even if the block changes, the location of the same dot position within the block is regularly affected by the short circuit. For example, if there is a short circuit in one place on the board wiring,
The output fluctuates regularly at the position of the image forming element connected to the short-circuited wiring. Therefore, if attention is paid to regular output fluctuations that repeat in block units, it is possible to accurately detect a short circuit that is difficult to detect because it is hidden by the output fluctuations of individual image forming elements. The regular output fluctuation for each block is preferably a CCD camera, a beam diameter measuring device, (in the case of an optical head such as an LED head), or an infrared camera (in the case of a thermal head).
Etc. to detect. Of course, in addition to this, it is also possible to perform a print inspection and detect it with the naked eye from white stripes or black stripes in block units.

As the regular output fluctuation in block units, for example, a decrease in output of the image forming element due to a decrease in drive current or drive voltage due to a short circuit is used. Other than this, for example, the image forming elements may be driven one by one, and it may be detected that an output is generated from an element that is not driven. For example, if there is a short circuit in the wiring to two adjacent elements, the output of the driven element will decrease, and a weak output will also be produced from the non-driven element. Therefore, the image forming elements are driven one by one, the output generated from the elements that are not driven is detected, and if there is regularity in block units, it is determined as a short circuit.

The output fluctuation due to the short circuit occurs in block units over the entire head even at one short circuit. However, the effect is greatest in the image forming element closest to the short-circuited portion. For example, assume that the electrodes of two image forming elements are short-circuited. Then, the largest output change occurs in the image forming element that is actually short-circuited, and in other image forming elements, a short-circuit current flows indirectly via the short-circuited point, and the farther the image-forming element is from the short-circuited point, the more the wiring resistance in the middle occurs. Since it is large, the output change is small. For this reason, it can be determined that, among the short-circuited image forming element candidates corresponding to the number of blocks, the portion having the largest output fluctuation is short-circuited. When a short circuit point is detected, the wiring is actually inspected to confirm the short circuit location. If repairable shorts, such as shorts between substrate wirings or bonding lines, the short-circuited portion is repaired, and if not possible, the image forming apparatus is reassembled. It should be noted that the detection of a short circuit in the present invention is to detect something that is likely to have a short circuit,
It does not necessarily mean that there is a short circuit.

[0009]

EXAMPLE FIG. 1 shows a first example. For the LED head, for example, 64 LEDs are integrated into one LED array, and 40 arrays are linearly arranged to form an LED head. The LED head is dynamically driven for each LED array, but may be dynamically driven with two LED arrays as one block. In the embodiment, the dynamic drive is 40 blocks. Each LED is wire-bonded to the substrate wiring, and the total number of bonding lines is 40 × 64 = 2560. L
Other configurations of the ED head, such as the arrangement of the housing and the lens array, the structure of the driving IC, etc., are well known, and a description thereof will be omitted.

The cause of the short circuit is shown in FIGS. FIG. 5 shows a short circuit in the board wiring 2, and since the LED array is dynamically driven, the board wiring 2 is composed of 64 individual wirings. FIG. 5 shows a short circuit caused by etching failure or the like as a short circuit between the individual wirings 4 and 6.

FIG. 6 shows a short circuit between the bonding lines.
One LED array 8 has 6 LEDs corresponding to the total number of LEDs.
There are four bonding wires. If these bonding wires come into contact with each other on the way, a short circuit occurs between the bonding wires. In the figure, the bonding lines 10 and 12 are in contact with each other on the way and a short circuit occurs.

FIG. 7 shows a short circuit due to double bonding to the bonding pad. Each LED of LED array 8
The electrode pad 16 is connected to 14, and wire bonding is performed to the bonding pad 20 of the substrate wiring 2 via the bonding wire 18. Although the position of the bonding pad 20 is confirmed by pattern recognition or the like for wire bonding, if the pattern recognition is erroneous, two bonding lines 18-1, 1 are formed on one bonding pad 20-1 as shown in FIG.
8-2 will be bonded. A similar short circuit
It is also caused by double wire bonding to the electrode pad 16 in the LED array 8.

FIG. 8 shows a short circuit between the electrode pads in the LED array 8. The electrode pad 16 is formed by etching or the like, but a short circuit occurs between bonding pads or between electrodes due to poor etching. 22 short circuit parts
Show as.

FIG. 4 shows an example of the output distribution in the LED head. If there is a short circuit at one location of the head, in the case of time-division driving, the effect thereof will appear periodically and repeatedly for each block. For example, as shown in FIG. 5, if there is a short circuit in the substrate wiring 2, the influence will occur on all the LEDs connected to the short-circuited individual wirings 4, 6. Further, if there is a short circuit between the bonding lines as shown in FIG. 6, all the LEDs are affected through the shorted bonding line. Here, the influence of the short circuit occurs when the LEDs are dynamically driven for each LED array and the positions of the LED arrays are the same. This is the same for the double bonding of FIG. 7 and the short circuit between the electrode pads of FIG. 8, and even if the position of the LED array is different, the LE position is the same in the array.
For D, the influence of a short circuit occurs regularly for each array.
Then, the influence of the short circuit is greatest in the LED in which the short circuit actually occurs. On the other hand, the further the LED is from the short-circuited portion, the smaller the influence of the short-circuiting. For example, assume that the bonding lines 10 and 12 are short-circuited as shown in FIG. Then, the LEDs that are actually connected to the short-circuited bonding wires 10 and 12 have the greatest influence.
Since the short circuit is caused from the board wiring 2 through the bonding wires 10 and 12, and the short circuit current flows again through the board wiring, the influence of the short circuit is small. This is the same when the cause of the short circuit is different, and the effect of the short circuit is greatest in the LED array in which the short circuit has actually occurred, and becomes smaller the further away from the LED array in which the short circuit occurs.

Returning to FIG. 1, detection of a short circuit in the embodiment will be described. First, the output of each of 2560 LEDs is sequentially measured. For measuring the output, for example, a CCD camera or a beam diameter measuring machine is used. Next, the average output of the surrounding m dots and the output difference between each LED are calculated. As the range of the surrounding m dots, for example, 2 dots for each 1 dot on the right and left or 10 dots for each 5 dots on the left and right are suitable. Of course, other than this, the output difference of each LED with respect to the average light emission output of each LED array 8 may be used. However, this method reduces the accuracy of short circuit detection. L
There is a regular output fluctuation in the ED array 8 due to variations in etching conditions and the like, and for example, in FIG. 4, the average light emission output is wavy like a sine wave. Therefore, if output variations are detected in LED array units, it is difficult to detect individual output variations due to gradual output variations due to variations in etching conditions within the array. Therefore, when the purpose is only to detect a short circuit, the output difference of the surrounding m dots with respect to the LED is expressed by (m is preferably 2 to 1).
0), preferably detected. In addition, when the output variation due to other causes such as defective selection of the LED array is also inspected at the same time, in addition to the output inspection in 1 dot units for surrounding m dots, the output inspection in 2 dot units for surrounding m dots, etc., 3 dots It suffices to sequentially perform output inspection and the like in units to detect output variations other than short circuits at the same time.

When the output difference from the surrounding m dots is calculated for each LED, this is written in the check table of FIG.
In the table, n is the dot number, for example 1-2 is the first LED
Means the second LED in the array. The numbers such as +5 or -7 in the lower column of the table indicate the output difference with respect to the average light emission output of surrounding m dots in%. Next, this check table is averaged in column units. Then, at the position where the light emission output regularly decreases due to the short circuit, the average light emission output on the column average extremely decreases, and the short circuit can be detected from this. For example, if there is a short circuit in the second LED of either LED array, averaging the 40 LED array
The second LED causes a large output drop. Another cause of the regular decrease in the output of the LEDs is that the LEDs at both ends of the LED array are easily damaged. Therefore, the fact that the average light emission output is low is not immediately short-circuited, and the top three columns with low average light emission output are selected and these are candidates for short-circuiting. For example, in the check table in the figure, the second LED, the seventh LED, and the 64th LED in each LED array are candidates. Therefore, regarding these three columns, the LED with the smallest output in each column, to be precise, the LE with the smallest output with respect to the average light emission output of surrounding m dots
Select D. Among the three columns, for the second column (column with LED number 2) having the lowest average light emission output, in addition to the LED having the smallest light emission output, the LED having the second smallest light emission output is selected. These four total LEDs are candidates for a short circuit.

Here, the four short-circuit candidates are obtained, but the output does not drop regularly at both ends of the array, and attention is paid only to the column with the greatest output drop, and the output drops the most in that column. It may be determined that the LED having a large number is short-circuited. The method of detecting the regularity of the output decrease is not limited to column averaging,
Anything that focuses on the fact that the output decreases regularly in block units may be used.

Next, regarding the inter-substrate wiring of the LED head, the bonding wire, the electrode pad, the bonding pad, etc.,
The candidate LED is inspected in an actual machine. If there is a short circuit between the individual wirings as a result of the inspection as shown in FIG. 5, the portion is trimmed and repaired. If the bonding wire is short-circuited in the middle, correct that part. If repair is not possible, disassemble the LED head and collect only recyclable parts.

[0019]

[Embodiment 2] In the embodiment of FIG. 1, it is utilized that the output is regularly reduced due to a short circuit. On the other hand, if there is a short circuit, a light emission output is generated even from an LED that is not originally driven. For example, as shown in FIG. 6, when there is a short circuit between the bonding wires 10 and 12, each LE of the LED head is
When D is made to sequentially emit light one by one, the LED connected to the adjacent bonding line 12 also emits weak light when the LED connected to the bonding line 10 is emitting light. This weak light emission is detected by a CCD camera, a dot diameter measuring device, or the like. The weak light emission is weak, and it is difficult to accurately detect it because it is hidden behind the light beam from the LED that should emit light. Therefore, the detection threshold value for weak light emission is lowered to detect whether the weak light emission has periodicity in array units. If there is periodicity, it is considered as a short circuit, and if there is no periodicity, it is assumed that the tail of the beam from the adjacent LED is erroneously detected. Also in this case, of the weak light emission from the LED that should not have originally emitted light, the one having the highest light emission intensity is inspected as the candidate for the short circuit and the actual device is inspected.

[0020]

[Third Embodiment] In addition to this, even if Fourier transform is used, L
A short circuit of the ED head can be detected. Such an inspection method is shown in FIG. Similar to the embodiment of FIG. 1, LE
Each LED of the D head is made to emit light one by one, and the light emission output distribution of the LED head is measured. Next, this light emission output distribution is Fourier transformed. The Fourier transform is performed as a spatial frequency with respect to the position of the light emitter, so that the regular output variation in the unit of one array becomes a Fourier transform component having a period of 64 dots. The object of detection is the output fluctuation of one array period, and to identify the LED with the largest output fluctuation among them. Therefore, the inverse Fourier transform is performed by removing the Fourier transform component of one array period from the Fourier transform data. When this inverse Fourier transform is compared with the original light emission output distribution, only regular output variations of one array period remain. The part where the maximum output reduction occurs is the short circuit part. Next, in order to improve the detection accuracy, check if the change is within the allowable range for the LED that has the maximum output error, and if it exceeds the allowable range, it is short-circuited and the actual LED head Inspect and repair defective parts.

[0021]

According to the present invention, in the case of a time-division drive type image forming apparatus, the fact that when one place has a short circuit, the effect thereof appears periodically and repeatedly in block units, is utilized. It is possible to easily and accurately detect a short circuit that is hidden behind the output variation of and difficult to detect.

[Brief description of drawings]

FIG. 1 is a flowchart showing detection of a short-circuited portion in the image device of the embodiment.

FIG. 2 is a flow chart showing detection of a short circuit portion in the second embodiment.

FIG. 3 is a flowchart showing detection of a short-circuited portion using Fourier transform in the third embodiment.

FIG. 4 is a characteristic diagram showing a light emission output distribution in an LED head.

FIG. 5 is a diagram showing a short circuit of board wiring in the LED head.

FIG. 6 is a diagram showing a short circuit between bonding lines in an LED head.

FIG. 7 is a diagram showing a short circuit due to double bonding in the LED head.

FIG. 8 is a diagram showing an electrode short circuit of an LED array in an LED head.

[Explanation of symbols]

 2 substrate wiring 4, 6 individual wiring 8 LED array 10, 12 bonding wire 14 LED 16 electrode pad 18 bonding wire 20 bonding pad 22 short-circuited portion

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 33/00 K 7376-4M

Claims (1)

[Claims] 1. A large number of image forming elements are arranged on a substrate, and these image forming elements are divided into a plurality of blocks.
In a method of manufacturing an image forming apparatus in which an image forming element is time-divisionally driven for each block, a step of inspecting an output of the image forming element, and detecting a regular output fluctuation occurring in a block cycle from the inspected output A method for manufacturing an image forming apparatus, comprising: a step; and a step of detecting a short circuit from a regular output fluctuation in the detected block period.