Electronic component, laser device, optical writing device and image forming apparatus

An electronic component includes: a base a seal body fixed to the base, constituting a hermetically sealed space together with the base; and an electronic component main body attached to a metal substrate via an adhesive containing silver within the hermetically sealed space. The base has a nickel plated layer, substantially not containing phosphor, on the seal body side.

BACKGROUND

The present invention relates to an electronic component, a laser device, an optical writing device using the laser device and an image forming apparatus using the optical writing device.

1. Technical Field

In a laser device, a seal body (cap) is fixed to a base (eyelet), and hermetically sealed space is formed with the base and the seal body. A laser light emitting element or the like as an electronic component main body is placed within the hermetically sealed space.

2. Related Art

An electronic component having a base, a seal body fixed to the base, forming hermetically sealed space together with the base, and an electronic component main body attached to a metal substrate via an adhesive containing silver within the hermetically sealed space, has inconvenience of leakage of minute electric current between an anode and a cathode of the electronic component.

The present inventors have found that sliver migration causes leakage of minute electric current. The silver migration means a phenomenon that ionized silver is precipitated in an insulating layer by electrochemical reaction to direct-current electric field. The silver migration generally occurs by moisture in atmosphere.

However, the present inventors have found another factor of the silver migration. That is, as shown in Japanese Published Unexamined Patent Application No. Hei 11-354685, when an electroless nickel plated layer is formed in the base, phosphor in the electroless nickel plated layer is discharged into the hermetically sealed space by heat in fixing of the seal body to the base by resistance welding or brazing. As the phosphor discharged in the hermetically sealed space has a high moisture absorption characteristic, it absorbs moisture in the hermetically sealed space and is ionized. It can be considered that the ionized phosphor further ionizes silver of the silver paste, thus causing silver migration.

SUMMARY

According to an aspect of the invention, there is provided an electronic component including: a base; a seal body fixed to the base, constituting a hermetically sealed space together with the base; and an electronic component main body attached to a metal substrate via an adhesive containing silver within the hermetically sealed space. The base has a nickel plated layer, substantially not containing phosphor, on the seal body side.

DETAILED DESCRIPTION

FIG. 1shows the outline of an image forming apparatus10according to an exemplary embodiment of the present invention. The image forming apparatus10has an image forming apparatus main body12. An image forming unit14is mounted in the image forming main body12. A discharge part16to be described later is provided in an upper part of the image forming apparatus main body12, and paper feeding units18, in the form of e.g. a two-layer unit, is provided in a lower part of the image forming apparatus main body12. Further, plural optional paper feeding units may be provided under the image forming apparatus main body12,

The respective paper feeding units18have a paper feeding unit main body20and a paper feed cassette22in which sheets are set. A pickup roller24is provided in an upper position around the back end of the paper feed cassette22, and a retard roller26and a feed roller28are provided in the rear of the pickup roller24.

A main conveyance path32is a paper passage from the feed roller28to a discharge outlet34. The main conveyance path32is positioned around the rear side of the image forming apparatus main body12(the left side surface inFIG. 1). The main conveyance path32has a portion approximately vertical from the paper feeding unit18to a fixing device36to be described later. A transfer device42and an image holder44to be described later are provided on the upstream side of the fixing device36of the main conveyance path32. Further, a registration roller38is provided on the upstream side of the transfer device42and the image holder44. Further, a discharge roller40is provided around the discharge outlet34of the main conveyance path32.

Accordingly, a sheet sent with the pickup roller24from the paper feed cassette22of the paper feeding unit18is handled in cooperation between the retard roller26and the feed roller28, and only the top sheet is guided to the main conveyance path32. The sheet is temporarily stopped with the registration roller38, then passed between the transfer device42to be described later and the image holder44at controlled timing. At this time, a developed image is fixed onto the sheet by the fixing device36, and the sheet is discharged with the discharge roller40from the discharge outlet34to the discharge part16.

Note that in the case of double-sided printing, the sheet is returned to a reverse path. That is, a portion of the main conveyance path32in front of the discharge roller40is branched into two parts and a switching device46is provided in the branching portion, and a reverse path48is formed from the branched part to the registration roller38. Conveyance rollers50ato50care provided on the reverse path48. In the case of double-sided printing, the switching device46is turned to a side to open the reverse path48, then the discharge roller40is reversed when the rear end of the sheet is brought into contact with the discharge roller40. The sheet is guided into the reverse path48then passed through the registration roller38, the transfer device42, the image holder44and the fixing device36, and is discharged from the discharge outlet34to the discharge part16.

The discharge part16has an inclined surface52rotatable with respect to the image forming apparatus main body12. The inclined surface52is gently sloped around the discharge outlet then gradually steeply sloped toward the front direction (rightward direction inFIG. 1). The portion of the discharge outlet corresponds to a lower end of the inclined surface52, while the portion of the high end corresponds to an upper end of the inclined surface52. The inclined surface52is supported, rotatably about the lower end, with the image forming apparatus main body12. As indicated with an alternate long and dashed double-dotted line inFIG. 1, when the inclined surface52is rotated upward to be opened, an opening54is formed such that a process cartridge64to be described later is attached/removed via the opening54.

The image forming unit14, which is e.g. an electrophotographic unit, has the image holder44having a photo conductor, a charging device56having e.g. a charging roller to uniformly charge the image holder44, an optical writing device58which optically writes a latent image on the image holder44charged by the charging device56, a developing unit60which visualizes the latent image on the image holder44formed by the optical writing device58with developing material, the transfer device42having e.g. a transfer roller to transfer the developed image by the developing unit60onto a sheet, a cleaning device62having e.g. a blade to clean developing material remaining on the image holder44, and the fixing device36which fixes the developed image on the sheet, transferred by the transfer device42, to the sheet.

The process cartridge64is the integration of the image holder44, the charging device56, the developing unit60and the cleaning device62. The process cartridge64is provided directly under the inclined surface52of the discharge part16. As described above, the process cartridge64is attached/removed via the opening54formed when the inclined surface52is opened.

FIG. 2shows the optical writing device58. The optical writing device58has a laser device68to emit a laser beam in a housing66. The laser beam emitted from the laser device68is collimated with a collimator lens70and reflected with a rotating polygon mirror72. The rotating polygon mirror72, having e.g. six deflecting surfaces (mirror surfaces), reflects the laser beam collimated with the collimator lens74toward an fθ lens76while it is rotated by a motor (not shown) at a predetermined constant angular velocity. The laser beam reflected with the rotating polygon mirror72is transmitted through the fθ lens76, thereby scans an image area on the image holder44in a fast-scanning direction at an approximately constant velocity.

FIGS. 3 and 4show the laser device68as an electronic component. The laser device68has a base78and a seal body80fixed to one surface of the base78. The seal body80has a cap82as a seal body main body. A transparent member84is formed at the center of an upper surface of the cap82. The transparent member84is sealed with seal glass86having e.g. a circular or polygonal shape. A flange88is formed in a lower surface of the seal body80, and the flange88is fixed to the base78by resistance welding or brazing. The base78and the seal body80form hermetically sealed space90.

An electronic component main body92is provided in the hermetically sealed space90. In the present exemplary embodiment, the electronic component92has a holding base94, a light sensing element96fixed to the holding base94and a light emitting element98fixed to the light sensing element96. The holding base94, the light sensing element96and the light emitting element98are built up in approximately parallel with each other.

The holding base94as a metal substrate, which is integrated with the base78, is formed by using an alloy containing iron and nickel. The holding base94and the light sensing element96are die-bonded with silver paste97in consideration of conductivity, thermal conductivity, adhesivity and the like. The light sensing element96is a semiconductor device of silicon. The light sensing element96is provided for receiving monitor light emitted from the light emitting element98for monitoring the light quantity of the light emitting element98. The light emitting element98is a semiconductor device of gallium arsenide. The laser beam emitted from the light emitting element98is outputted via the seal glass86from the transparent member84. The light sensing element96and the light emitting element98are die-bonded with brazing filler metal of e.g. Au—Sn alloy.

First lead100and second lead102, insulated by the base78, are projected in the hermetically sealed space90. The first lead100is connected to the anode of the light sensing element96via a metal first connection line (wire)104. The second lead102is connected to the cathode of the light emitting element98via a metal second connection line (wire)106. A third lead108, as a common electrode for the cathode of the light sensing element96and the anode of the light emitting element98, is connected to the base78.

FIG. 5shows a driver to drive the laser device68. The first lead100is grounded via a resistor110. The second lead102is grounded via a first current regulator112and a second current regulator114. The third lead108as a common electrode is connected to a constant voltage source of e.g. plus 5 V.

A voltage occurred between the both terminals of the resistor110is converted to a digital signal by an AD converter116. The digital signal is compared with a reference digital voltage value generated by a reference part118by a comparator120. The result of comparison by the comparator120is inputted into a controller122having e.g. a CPU. The controller122outputs a digital current regulation value corresponding to the input. The digital current regulation value is inputted into a first DA converter124and a second DA converter126and converted to analog current regulation values. A current flowing through the first current regulator112is regulated with the analog current regulation value converted by the first DA converter124. Further, the analog current regulation value converted by the second DA converter126is inputted into a multiplication-type DA converter128. The multiplication-type DA converter128inputs a laser intensity conversion signal, and outputs an analog current regulation value obtained by multiplying the laser intensity conversion signal by the analog current regulation value inputted from the second DA converter126. A current flowing through the second current regulator114is regulated based on the analog current regulation value outputted from the multiplication-type DA converter128.

In the above driver, when a laser modulation signal is inputted, a current flows through the light emitting element98, then a laser beam is outputted from the light emitting element98. At this time, monitor light is inputted into the light sensing element96, and a current corresponding to the light quantity of the monitor light flows via the light sensing element96. The current is converted to a voltage and compared with a reference value by the comparator120. Then a regulation value is calculated by the controller122, and the currents flowing through the first current regulator112and the second current regulator114are regulated. That is, as the variation of light quantity of the laser beam emitted from the light emitting element98in accordance with temperature or the like is monitored with the light sensing element96and feedback is performed, and a predetermined quantity of the laser beam, without variation due to temperature or the like, can be emitted.

FIGS. 6 and 7show the details of a joint portion between the base78and the cap82. The base78has a nickel plated layer132as a first plated layer on a substrate130containing iron and nickel. The nickel plated layer132does not substantially contain phosphor. Note that, in the phrase “does not substantially containing phosphor”, natural phosphor is excluded from “phosphor”, and the amount of phosphor (natural phosphor) contained in the nickel plated layer is several ppm or less (less than 10 ppm). For example, an electroless nickel plated layer containing 0.1 to 2.0 wt % of boron is obtained by dipping a substrate in nickel-boron (Ni—B) plating solution containing boron. Otherwise, a nickel plated layer not substantially containing phosphor can be formed by electroplating.

As a second plated layer of the base78, a gold plated layer134is formed. The gold plated layer134is formed by dipping the substrate130, on which the nickel plated layer132is formed, in plating solution containing gold. The gold plated layer134has a thickness of 0.1 to 1.0 μm.

On the other hand, as the cap82has a simple shape, a nickel plated layer138by electroplating is formed on a substrate136. The base78and the cap82are joined by e.g. resistance welding. The temperature of the joint portion upon resistance welding is 1400° C. to 1450° C. The melting temperature of the nickel plated layer132of the base78and the melting temperature of the nickel plated layer138of the cap82are both 1400° C. to 1450° C. while the melting temperature of the gold plated layer134is 1000° C. to 1100° C. As shown inFIG. 7, upon resistance welding, the nickel plated layer132and the nickel plated layer138are brought into contact with each other as alloy-junction, and a firm joint organization is formed. Further, as the hardness of the nickel plated layer132is 700 to 800 Hv (Vickers hardness), joint with reduced distortion can be performed. For example, even when the joint portion has irregularity, a small area of contact can be maintained, the resistance of the contact portion can be reduced, and heat generation by resistance can be reduced.

As the joint portion between the base78and the cap82does not substantially contain phosphor, leakage of phosphor component in the hermetically sealed space90does not substantially occur, and the probability of occurrence of sliver migration can be reduced.

FIG. 8shows a comparative example regarding the joint portion between the base78and the cap82. In the comparative example, as a first plated layer of the base78, an electroless nickel plated layer140containing phosphor is formed. That is, the electroless nickel plated layer140, formed by dipping a substrate in a nickel-phosphor (Ni—P) plating solution, contains 10 wt % of phosphor. The melting temperature of the electroless nickel plated layer140is about 900° C. As in the case of the above exemplary embodiment, the second plated layer of the base78is a gold plated layer, however, its thickness is equal to or greater than 1.0 μm since the contact resistance of the electroless nickel plated layer140is higher.

The temperature of the joint portion upon resistance welding is about 1200° C. The electroless nickel plated layer140first melts, then the phosphor in the electroless nickel plated layer140melts into the gold plated layer134, then a part of the melted phosphor component sublimates at 250° C. or higher, and discharged as phosphoric acid (P2O5) into the hermetically sealed space90. The discharged phosphoric acid having marked moisture absorption characteristic absorbs moisture in the hermetically sealed space90, and ionized as follows.
P2O5+3H2O→2H3PO4
H3PO4H++H2PO4−
H2PO4−H++HPO42−
HPO42−H++PO43−

On the other hand, in the silver paste97connecting the holding base94and the light sensing element96, as distortion remains in Ag elements existing among resin containing organic materials, the Ag element group is easily dissociated from the paste material. In this case, as silver (Ag) as a main component of the silver paste has a large ion radius (1.2 Å), dissociation is suppressed at normal times. However, as described above, as trivalent phosphor ions exist in the hermetically sealed space, dissociation of sliver is promoted. In the light sensing element, as the potential of the cathode terminal is higher than that of the anode terminal by an applied inverse bias voltage, the dissociated silver ions move from the cathode of the light sensing element96toward the anode by the electric field, and precipitate as silver. The dissociation and precipitation are repeated, thereby the precipitation of silver continues in an area surrounded with a dotted line inFIG. 9. As a result, the insulation distance between the cathode and the anode becomes short, or disappears. This phenomenon is silver migration.

In this manner, when the insulation distance of the light sensing element96becomes short or disappears, a leak current is generated between the terminals, and the light quantity of the monitor light from the light emitting element98cannot be correctly detected. As a result, feedback cannot be performed, and the quantity of light emission of the light emitting element98is reduced. When the quantity of light emission of the light emitting element98is reduced, image forming density is reduced in the image forming apparatus, and further, an image cannot be formed.

On the other hand, according to the above-described present exemplary embodiment of the present invention, as the nickel plated layer132of the base78does not substantially contain phosphor, the occurrence of silver migration can be prevented. Further, as an alloy is formed between the nickel plated layer132of the base78and the nickel plated layer138of the cap82upon resistance welding, the joint strength can be increased. Further, as the resistance of the joint portion can be reduced even when the thickness of the gold plated layer134is reduced, there is an economical merit.

FIG. 10shows another exemplary embodiment of the present invention. In the above-described previous exemplary embodiment, the light sensing element96is overlaid on the light emitting element98, while in the present exemplary embodiment, the light sensing element96is fixed to the base78below the light emitting element98, and the light sensing element96receives monitor light emitted from the light emitting element98below the light emitting element98. In this case, as indicated with alphabet M, the anode and the cathode (a common electrode of the base78) of the light sensing element96are joined via the silver paste97, and there is a probability of occurrence of silver migration.

However, as described above, as the nickel plated layer of the base78does not substantially contain phosphor, the occurrence of silver migration can be prevented.