Abstract:
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.

Description:
BACKGROUND 
       [0001]    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. 
         [0002]    1. Technical Field 
         [0003]    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. 
         [0004]    2. Related Art 
         [0005]    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. 
         [0006]    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. 
         [0007]    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 
       [0008]    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. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
           [0010]      FIG. 1  is a cross-sectional view of an image forming apparatus according to an exemplary embodiment of the present invention; 
           [0011]      FIG. 2  is a perspective view of an optical writing device according to the exemplary embodiment of the present invention; 
           [0012]      FIG. 3  is a cross-sectional view of a laser device according to the exemplary embodiment of the present invention; 
           [0013]      FIG. 4  is a cross-sectional view of the laser device according to the exemplary embodiment of the present invention cut along a line A-A in  FIG. 3 ; 
           [0014]      FIG. 5  is a block diagram showing a driver to drive the laser device according to the exemplary embodiment of the present invention; 
           [0015]      FIG. 6  is a cross-sectional view of a base  78  and a cap  82  before junction in the laser device according to the exemplary embodiment of the present invention; 
           [0016]      FIG. 7  is a cross-sectional view of the base  78  and the cap  82  after the junction in the laser device according to the exemplary embodiment of the present invention; 
           [0017]      FIG. 8  is a cross-sectional view of the base  78  and the cap  82  after the junction in a comparative example; 
           [0018]      FIG. 9  is a cross-sectional view showing occurrence of silver migration in the laser device in the comparative example; and 
           [0019]      FIG. 10  is a side view of the laser device according to another exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Next, exemplary embodiments of the present invention will be described with reference to the drawings. 
         [0021]      FIG. 1  shows the outline of an image forming apparatus  10  according to an exemplary embodiment of the present invention. The image forming apparatus  10  has an image forming apparatus main body  12 . An image forming unit  14  is mounted in the image forming main body  12 . A discharge part  16  to be described later is provided in an upper part of the image forming apparatus main body  12 , and paper feeding units  18 , in the form of e.g. a two-layer unit, is provided in a lower part of the image forming apparatus main body  12 . Further, plural optional paper feeding units may be provided under the image forming apparatus main body  12 , 
         [0022]    The respective paper feeding units  18  have a paper feeding unit main body  20  and a paper feed cassette  22  in which sheets are set. A pickup roller  24  is provided in an upper position around the back end of the paper feed cassette  22 , and a retard roller  26  and a feed roller  28  are provided in the rear of the pickup roller  24 . 
         [0023]    A main conveyance path  32  is a paper passage from the feed roller  28  to a discharge outlet  34 . The main conveyance path  32  is positioned around the rear side of the image forming apparatus main body  12  (the left side surface in  FIG. 1 ). The main conveyance path  32  has a portion approximately vertical from the paper feeding unit  18  to a fixing device  36  to be described later. A transfer device  42  and an image holder  44  to be described later are provided on the upstream side of the fixing device  36  of the main conveyance path  32 . Further, a registration roller  38  is provided on the upstream side of the transfer device  42  and the image holder  44 . Further, a discharge roller  40  is provided around the discharge outlet  34  of the main conveyance path  32 . 
         [0024]    Accordingly, a sheet sent with the pickup roller  24  from the paper feed cassette  22  of the paper feeding unit  18  is handled in cooperation between the retard roller  26  and the feed roller  28 , and only the top sheet is guided to the main conveyance path  32 . The sheet is temporarily stopped with the registration roller  38 , then passed between the transfer device  42  to be described later and the image holder  44  at controlled timing. At this time, a developed image is fixed onto the sheet by the fixing device  36 , and the sheet is discharged with the discharge roller  40  from the discharge outlet  34  to the discharge part  16 . 
         [0025]    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 path  32  in front of the discharge roller  40  is branched into two parts and a switching device  46  is provided in the branching portion, and a reverse path  48  is formed from the branched part to the registration roller  38 . Conveyance rollers  50   a  to  50   c  are provided on the reverse path  48 . In the case of double-sided printing, the switching device  46  is turned to a side to open the reverse path  48 , then the discharge roller  40  is reversed when the rear end of the sheet is brought into contact with the discharge roller  40 . The sheet is guided into the reverse path  48  then passed through the registration roller  38 , the transfer device  42 , the image holder  44  and the fixing device  36 , and is discharged from the discharge outlet  34  to the discharge part  16 . 
         [0026]    The discharge part  16  has an inclined surface  52  rotatable with respect to the image forming apparatus main body  12 . The inclined surface  52  is gently sloped around the discharge outlet then gradually steeply sloped toward the front direction (rightward direction in  FIG. 1 ). The portion of the discharge outlet corresponds to a lower end of the inclined surface  52 , while the portion of the high end corresponds to an upper end of the inclined surface  52 . The inclined surface  52  is supported, rotatably about the lower end, with the image forming apparatus main body  12 . As indicated with an alternate long and dashed double-dotted line in  FIG. 1 , when the inclined surface  52  is rotated upward to be opened, an opening  54  is formed such that a process cartridge  64  to be described later is attached/removed via the opening  54 . 
         [0027]    The image forming unit  14 , which is e.g. an electrophotographic unit, has the image holder  44  having a photo conductor, a charging device  56  having e.g. a charging roller to uniformly charge the image holder  44 , an optical writing device  58  which optically writes a latent image on the image holder  44  charged by the charging device  56 , a developing unit  60  which visualizes the latent image on the image holder  44  formed by the optical writing device  58  with developing material, the transfer device  42  having e.g. a transfer roller to transfer the developed image by the developing unit  60  onto a sheet, a cleaning device  62  having e.g. a blade to clean developing material remaining on the image holder  44 , and the fixing device  36  which fixes the developed image on the sheet, transferred by the transfer device  42 , to the sheet. 
         [0028]    The process cartridge  64  is the integration of the image holder  44 , the charging device  56 , the developing unit  60  and the cleaning device  62 . The process cartridge  64  is provided directly under the inclined surface  52  of the discharge part  16 . As described above, the process cartridge  64  is attached/removed via the opening  54  formed when the inclined surface  52  is opened. 
         [0029]      FIG. 2  shows the optical writing device  58 . The optical writing device  58  has a laser device  68  to emit a laser beam in a housing  66 . The laser beam emitted from the laser device  68  is collimated with a collimator lens  70  and reflected with a rotating polygon mirror  72 . The rotating polygon mirror  72 , having e.g. six deflecting surfaces (mirror surfaces), reflects the laser beam collimated with the collimator lens  74  toward an fθ lens  76  while it is rotated by a motor (not shown) at a predetermined constant angular velocity. The laser beam reflected with the rotating polygon mirror  72  is transmitted through the fθ lens  76 , thereby scans an image area on the image holder  44  in a fast-scanning direction at an approximately constant velocity. 
         [0030]      FIGS. 3 and 4  show the laser device  68  as an electronic component. The laser device  68  has a base  78  and a seal body  80  fixed to one surface of the base  78 . The seal body  80  has a cap  82  as a seal body main body. A transparent member  84  is formed at the center of an upper surface of the cap  82 . The transparent member  84  is sealed with seal glass  86  having e.g. a circular or polygonal shape. A flange  88  is formed in a lower surface of the seal body  80 , and the flange  88  is fixed to the base  78  by resistance welding or brazing. The base  78  and the seal body  80  form hermetically sealed space  90 . 
         [0031]    An electronic component main body  92  is provided in the hermetically sealed space  90 . In the present exemplary embodiment, the electronic component  92  has a holding base  94 , a light sensing element  96  fixed to the holding base  94  and a light emitting element  98  fixed to the light sensing element  96 . The holding base  94 , the light sensing element  96  and the light emitting element  98  are built up in approximately parallel with each other. 
         [0032]    The holding base  94  as a metal substrate, which is integrated with the base  78 , is formed by using an alloy containing iron and nickel. The holding base  94  and the light sensing element  96  are die-bonded with silver paste  97  in consideration of conductivity, thermal conductivity, adhesivity and the like. The light sensing element  96  is a semiconductor device of silicon. The light sensing element  96  is provided for receiving monitor light emitted from the light emitting element  98  for monitoring the light quantity of the light emitting element  98 . The light emitting element  98  is a semiconductor device of gallium arsenide. The laser beam emitted from the light emitting element  98  is outputted via the seal glass  86  from the transparent member  84 . The light sensing element  96  and the light emitting element  98  are die-bonded with brazing filler metal of e.g. Au—Sn alloy. 
         [0033]    First lead  100  and second lead  102 , insulated by the base  78 , are projected in the hermetically sealed space  90 . The first lead  100  is connected to the anode of the light sensing element  96  via a metal first connection line (wire)  104 . The second lead  102  is connected to the cathode of the light emitting element  98  via a metal second connection line (wire)  106 . A third lead  108 , as a common electrode for the cathode of the light sensing element  96  and the anode of the light emitting element  98 , is connected to the base  78 . 
         [0034]      FIG. 5  shows a driver to drive the laser device  68 . The first lead  100  is grounded via a resistor  110 . The second lead  102  is grounded via a first current regulator  112  and a second current regulator  114 . The third lead  108  as a common electrode is connected to a constant voltage source of e.g. plus 5 V. 
         [0035]    A voltage occurred between the both terminals of the resistor  110  is converted to a digital signal by an AD converter  116 . The digital signal is compared with a reference digital voltage value generated by a reference part  118  by a comparator  120 . The result of comparison by the comparator  120  is inputted into a controller  122  having e.g. a CPU. The controller  122  outputs a digital current regulation value corresponding to the input. The digital current regulation value is inputted into a first DA converter  124  and a second DA converter  126  and converted to analog current regulation values. A current flowing through the first current regulator  112  is regulated with the analog current regulation value converted by the first DA converter  124 . Further, the analog current regulation value converted by the second DA converter  126  is inputted into a multiplication-type DA converter  128 . The multiplication-type DA converter  128  inputs 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 converter  126 . A current flowing through the second current regulator  114  is regulated based on the analog current regulation value outputted from the multiplication-type DA converter  128 . 
         [0036]    In the above driver, when a laser modulation signal is inputted, a current flows through the light emitting element  98 , then a laser beam is outputted from the light emitting element  98 . At this time, monitor light is inputted into the light sensing element  96 , and a current corresponding to the light quantity of the monitor light flows via the light sensing element  96 . The current is converted to a voltage and compared with a reference value by the comparator  120 . Then a regulation value is calculated by the controller  122 , and the currents flowing through the first current regulator  112  and the second current regulator  114  are regulated. That is, as the variation of light quantity of the laser beam emitted from the light emitting element  98  in accordance with temperature or the like is monitored with the light sensing element  96  and feedback is performed, and a predetermined quantity of the laser beam, without variation due to temperature or the like, can be emitted. 
         [0037]      FIGS. 6 and 7  show the details of a joint portion between the base  78  and the cap  82 . The base  78  has a nickel plated layer  132  as a first plated layer on a substrate  130  containing iron and nickel. The nickel plated layer  132  does 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. 
         [0038]    As a second plated layer of the base  78 , a gold plated layer  134  is formed. The gold plated layer  134  is formed by dipping the substrate  130 , on which the nickel plated layer  132  is formed, in plating solution containing gold. The gold plated layer  134  has a thickness of 0.1 to 1.0 μm. 
         [0039]    On the other hand, as the cap  82  has a simple shape, a nickel plated layer  138  by electroplating is formed on a substrate  136 . The base  78  and the cap  82  are 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 layer  132  of the base  78  and the melting temperature of the nickel plated layer  138  of the cap  82  are both 1400° C. to 1450° C. while the melting temperature of the gold plated layer  134  is 1000° C. to 1100° C. As shown in  FIG. 7 , upon resistance welding, the nickel plated layer  132  and the nickel plated layer  138  are brought into contact with each other as alloy-junction, and a firm joint organization is formed. Further, as the hardness of the nickel plated layer  132  is 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. 
         [0040]    As the joint portion between the base  78  and the cap  82  does not substantially contain phosphor, leakage of phosphor component in the hermetically sealed space  90  does not substantially occur, and the probability of occurrence of sliver migration can be reduced. 
         [0041]      FIG. 8  shows a comparative example regarding the joint portion between the base  78  and the cap  82 . In the comparative example, as a first plated layer of the base  78 , an electroless nickel plated layer  140  containing phosphor is formed. That is, the electroless nickel plated layer  140 , 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 layer  140  is about 900° C. As in the case of the above exemplary embodiment, the second plated layer of the base  78  is 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 layer  140  is higher. 
         [0042]    The temperature of the joint portion upon resistance welding is about 1200° C. The electroless nickel plated layer  140  first melts, then the phosphor in the electroless nickel plated layer  140  melts into the gold plated layer  134 , then a part of the melted phosphor component sublimates at 250° C. or higher, and discharged as phosphoric acid (P 2 O 5 ) into the hermetically sealed space  90 . The discharged phosphoric acid having marked moisture absorption characteristic absorbs moisture in the hermetically sealed space  90 , and ionized as follows. 
         [0000]      P 2 O 5 +3H 2 O→2H 3 PO 4    
         [0000]      H 3 PO 4           H + +H 2 PO 4 − 
         [0000]      H 2 PO 4 −         H + +HPO 4   2 − 
         [0000]      HPO 4   2 −         H + +PO 4   3 − 
         [0043]    On the other hand, in the silver paste  97  connecting the holding base  94  and the light sensing element  96 , 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 element  96  toward 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 in  FIG. 9 . As a result, the insulation distance between the cathode and the anode becomes short, or disappears. This phenomenon is silver migration. 
         [0044]    In this manner, when the insulation distance of the light sensing element  96  becomes short or disappears, a leak current is generated between the terminals, and the light quantity of the monitor light from the light emitting element  98  cannot be correctly detected. As a result, feedback cannot be performed, and the quantity of light emission of the light emitting element  98  is reduced. When the quantity of light emission of the light emitting element  98  is reduced, image forming density is reduced in the image forming apparatus, and further, an image cannot be formed. 
         [0045]    On the other hand, according to the above-described present exemplary embodiment of the present invention, as the nickel plated layer  132  of the base  78  does not substantially contain phosphor, the occurrence of silver migration can be prevented. Further, as an alloy is formed between the nickel plated layer  132  of the base  78  and the nickel plated layer  138  of the cap  82  upon 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 layer  134  is reduced, there is an economical merit. 
         [0046]      FIG. 10  shows another exemplary embodiment of the present invention. In the above-described previous exemplary embodiment, the light sensing element  96  is overlaid on the light emitting element  98 , while in the present exemplary embodiment, the light sensing element  96  is fixed to the base  78  below the light emitting element  98 , and the light sensing element  96  receives monitor light emitted from the light emitting element  98  below the light emitting element  98 . In this case, as indicated with alphabet M, the anode and the cathode (a common electrode of the base  78 ) of the light sensing element  96  are joined via the silver paste  97 , and there is a probability of occurrence of silver migration. 
         [0047]    However, as described above, as the nickel plated layer of the base  78  does not substantially contain phosphor, the occurrence of silver migration can be prevented. 
         [0048]    The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.