JP3869575B2 - Semiconductor laser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a can seal type semiconductor laser in which the periphery of a laser chip is hermetically sealed. More particularly, the present invention relates to an inexpensive semiconductor laser particularly suitable for use in a pickup light source such as a DVD (digital video disk), an LBP (laser beam printer), and a DVD-ROM.
[0002]
[Prior art]
A semiconductor laser used for a conventional DVD light source has a structure as shown in FIG. That is, the laser chip 23 is covered with the cap 24 and hermetically sealed because it is necessary to protect the laser chip 23 from the outside air in order to ensure reliability.
[0003]
4A is a plan view, FIG. 4B is a partially sectional side view, and FIG. 4C is a sectional explanatory view when the cap 24 is welded to the stem 21. 21 is a stem formed integrally with a pedestal 21a by cold forging of metal or the like, and is provided with two through holes 21b as shown in FIG. 4C, and leads 26 and 27 are low melting point glass 29 and the like. And hermetically sealed (hermetic sealing). A laser chip 23 is bonded to the base 21a via a submount 22 made of a silicon substrate or the like, and wire-bonded to the tips of the leads 26 and 27. Further, a common lead 28 is bonded to the bottom side of the stem by welding or the like. A cap 24 is attached to the stem 21 by welding or the like in order to hermetically seal the upper portion of the stem 21 around the laser chip 23. A through-hole is provided in the laser beam passage portion of the cap 24, and the window glass 25 is bonded with low melting point glass or the like. In this example, since both the laser diode and the photodiode for monitoring the output of the laser diode are provided, the leads 26 and 27 connected to the respective one electrode and the other electrode are made common. The three leads connected to the common lead 28 are led out of the package. Although not shown, the photodiode is formed with a recess at the center of the stem 21 and is provided in the recess or directly on the submount 22.
[0004]
As shown in FIG. 4C, the above-described welding of the cap 24 and the stem 21 is performed from above and below so that the current is concentrated by the protrusion 24b provided on the bottom surface side of the flange 24a at the bottom of the cap 24. The electrodes 31 and 32 are sandwiched and welded. The outer peripheral surface A of the stem 21 serves as a reference surface for positioning. Reference numeral 21c denotes a notch for positioning in the rotational direction.
[0005]
[Problems to be solved by the invention]
The stem portion of the conventional semiconductor laser having the structure shown in FIG. 4 is formed by molding a stem together with a pedestal using a cold metal forging press as described above. The pedestal formed integrally with the stem must have a perpendicularity with respect to the bottom surface of the stem of about 1 °, and the outer diameter dimensional accuracy of the stem is required to have a tolerance of less than about 0.03 mm. In order to manufacture by cold forging, a very high mold accuracy is required. Therefore, there is a problem that the maintenance cost of the mold is increased and the unit price of the metal stem is increased.
[0006]
Furthermore, when the metal stem is molded, a hole must be made in the stem and the lead must be sealed later with glass. Therefore, even when a lead having a thickness of about 0.45 mm is encapsulated, the hole diameter provided in the stem needs to be about 1 mmφ, and the outermost diameter of the stem including the welded portion of the cap and the portion used as the reference surface is about 5.6 mm. With a small stem, the degree of freedom of space for arranging the leads is limited, and the leads must be separately sealed with glass, which further increases man-hours and increases costs.
[0007]
The present invention solves such problems, has a high degree of design freedom, can be easily manufactured, and has a dimensional accuracy comparable to that of a conventional can-seal type semiconductor laser and a small size that can provide a mounting reference surface. And an inexpensive semiconductor laser.
[0008]
[Means for Solving the Problems]
The semiconductor laser according to the present invention, a resin stem having a plurality of leads fixed to the resin portion of the disc-shaped by Rukoto are integrally molded by resin so that a plurality of leads is exposed vertically made of a conductive material, said plurality of is the formed into one integral leads, and the base you exposed on the resin portion, is formed so as to be exposed on the resin portion with pedestal integral with the disc-shaped resin from both ends of the pedestal A protrusion extending toward the end of the portion, a laser chip fixed to the pedestal, a periphery of the laser chip and a light transmission window at the top, and abutting against the protrusion to the stem It consists of a cap that is fixed to.
[0009]
With this structure, it is possible to easily form a resin stem simply by fixing the lead with a mold and pouring the resin, and the man-hour can be greatly reduced and the manufacturing cost can be reduced. On the other hand, it is difficult to maintain a constant reference surface for the outer diameter and height by using resin, but the required reference surface can be obtained by using a metal that constitutes the base or a metal such as a cap. Can do.
[0010]
Among the plurality of leads, the pedestal and not the integral lead by Rukoto fixed by different lead fixing resin and the base and the resin portion, the reduction of the lead holding force due to the stem is made of resin Can be supplemented .
[0011]
By forming a stepped skirt portion covering the upper and side portions around the stem at the bottom of the cap, the outside of the cap can be removed even if the diameter of the resin stem is not precisely formed. It is preferable because the mounting position can be accurately determined by the diameter, and the upper surface of the skirt portion can be used as a reference surface for positioning the laser chip (distance from the laser chip).
[0012]
Since the cap is made of metal and the cap is fixed to the stem with an adhesive, the heat transmitted to the pedestal can be efficiently radiated from the cap. In addition, although an epoxy resin etc. can be used for an adhesive agent , a thing with favorable heat conductivity is preferable, and an adhesive with favorable heat conductivity is good heat conductivity, such as a metal filler like a silver paste, for example. It means an adhesive mixed with material.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, the semiconductor laser of the present invention will be described with reference to the drawings.
[0014]
The semiconductor laser of the present invention is a resin so that a plurality of leads 11 to 13 made of a conductive material are exposed vertically, as shown in FIG. A pedestal 15 is electrically connected to the resin stem 1 integrally formed by the member 14 and one lead 11 of the plurality of leads 11 to 13. The laser chip 2 is fixed to the base 15. The laser chip 2 is mounted on a silicon submount 3, and the submount 3 is fixed on a pedestal 15. The pedestal 15 is provided with a light receiving element 4 for monitoring the output of the laser chip 2. A cap 5 is placed around the laser chip 2 and the like, and is fixed to the stem 1 with an adhesive 6 or the like. A light transmission window 51 is formed on the top of the cap 5. In some cases, a window glass or the like is hermetically sealed to the transmission window 51.
[0015]
As shown in a plan view and a side view of FIG. 2, the stem 1 has three leads 11 to 13 fixed by an insulating resin member 14 in this example. One of the leads 11 is formed integrally with the pedestal 15, the pedestal 15 is formed at the upper part of the resin member 14, and the lead extends as the common lead 11 at the lower part. On the upper part of the resin member 14, a protrusion 16 is further integrated with the pedestal 15 and extends to the outer periphery of the stem 1 so as to be exposed on the upper part of the resin member 14. The protruding portion 16 is provided with a certain size so as to be slightly exposed from the surface of the resin member 14, and has a structure in which the cap 5 is placed and fixed thereon. That is, heat generated in the laser chip 2 escapes to the cap 5 through the pedestal 15 and the protrusions 16 and can be radiated from the cap 5. Further, the resin member 14 cannot be formed with a dimensional accuracy as high as that of metal, and it is difficult to set the positioning reference surface of the laser chip 2 on the stem 1. Therefore, the position of the projection 16 with respect to the base 15 is accurately determined, and the cap 5 is provided so as to abut against the projection 16 so that the flat portion B of the skirt portion 52 of the cap 5 is provided. A reference surface for positioning the laser chip 2 can be used.
[0016]
As shown in FIG. 2, the protrusion 16 is formed so as to extend from the pedestal 15 portion to the peripheral edge of the stem 1, and is formed in a U shape, for example, in a planar shape. This protrusion 16 is not limited to this shape, and is preferably provided along the circumferential direction at a portion where the bottom of the cap 5 hits around the stem, from the viewpoint of heat dissipation and fixing of the cap 5. A notch 15a provided at the upper center of the pedestal 15 is for preventing light emitted from the laser chip 2 from hitting, and reference numeral 17 in FIG. Since the stem 1 is made of resin at the time of wire bonding, the holding power of the lead is reduced compared to the case where the lead is sealed with a low melting point glass. This is to prevent the decrease in the temperature.
[0017]
The resin member 14 is preferably heat resistant when the temperature tends to rise when soldering when the completed element is incorporated into a circuit board or the like, and for example, a liquid crystal polymer can be used. However, an ordinary resin such as PPS (polyphenylene sulfide) can also be used. The resin member 14 has a thickness of about 0.8 to 1 mm, and can be made slightly thinner than a conventional metal (about 1.1 to 1.3 mm). In addition, 14a-14c are the notch parts for the positioning with respect to the rotation formed in the stem 1 similarly to the past. Such notches 14a to 14c can also be easily formed in a desired shape simply by forming protrusions on the mold.
[0018]
In order to manufacture the stem 1, for example, leads 11 to 13 formed by punching and bending the pedestal 15, the protrusions 16, and the like in advance are set in a mold in which a cavity having the shape of the resin member 14 is formed. The stem 1 in which the leads 11 to 13 are fixed in the resin member 14 can be formed by injecting and curing the resin. In addition, several sets of the leads 11 to 13 are connected like a lead frame, and several cavities are provided in one die so that several tens of stems 1 can be simultaneously manufactured. can do.
[0019]
The laser chip 2 is formed so as to emit laser light, but its size is very small, about 250 μm × 250 μm, and is usually about 0.8 × 1 mm in order to facilitate its handling. Bonding is performed on a submount 3 made of a silicon substrate or the like. One electrode is directly connected to the submount 3 and connected to the common lead 11 by a conductive adhesive, and the other electrode is connected to the lead 13 by wire bonding via the electrically floating portion of the submount 3. It is connected. The submount 3 on which the laser chip 2 is mounted is conveyed by the suction collet, aligned with the upper surface of the protrusion 16 as a reference, and mounted on the pedestal 15. By using the upper surface of the projecting portion 16 as a reference, a cap 5 (described later) is fixed on the projecting portion 16, so that the position of the laser chip 2 is accurate with respect to the reference surface B of the skirt portion 52 of the cap 5. Well assembled. Similarly, the light receiving element 4 for monitoring the light emission output of the laser chip 2 is bonded to the pedestal 15, one electrode of which is connected to the common lead 11 through the pedestal 15, and the other electrode is wire bonding (not shown). Thus, the lead 12 is electrically connected. The light receiving element 4 can also be formed directly on the submount 3.
[0020]
A cap 5 is provided around the laser chip 2 by being bonded to the stem 1. The cap 5 is preferably made of a material having good thermal conductivity such as copper, but may be a metal such as iron. Further, matte silver plating or the like is preferably applied because it is easy to prevent irregular reflection of light on the inner surface. Note that a through-hole through which laser light passes is provided at the center of the top of the cap 5, and a window 51 is formed. Further, a stepped skirt portion 52 is formed at the bottom, the stepped flat portion is used as a reference surface B for positioning, and a portion covering the stem 1 of the skirt portion 52 has an outer diameter of the product. It is a standard. Since the cap 5 is made of metal, its dimensional accuracy is formed with extremely high accuracy, and always has a reference surface and a reference diameter with constant dimensions regardless of variations in the dimensions of the resin stem 1. The cap 5 is bonded to the stem with an adhesive made of an epoxy resin or the like. However, in order to improve the dissipation of the heat generated in the laser chip 2, a material having good heat conduction is preferable, and a metal such as silver is used. What mixed the filler is preferable.
[0021]
According to the semiconductor laser of the present invention, since the stem is formed by fixing the lead with the resin member, it requires a complicated forming process for forming a conventional metal plate by a cold forging method. It can be formed at a very low cost. In addition, there is no need to attach the lead to the glass later, and no man-hours for attaching the lead are required, and a space larger than the thickness of the lead is not required. The degree of freedom increases. Also, if the pedestal is formed integrally with the lead and molded with resin, the squareness etc. can be molded very precisely due to the precision of the mold, and a high-performance semiconductor laser with small bending can be obtained. Can do. On the other hand, it is conceivable that heat dissipation and dimensional accuracy become rough as a disadvantage of the stem made of resin. However, with respect to heat dissipation, a protrusion 16 that is exposed from the resin member 14 is provided integrally with the base 15 on which the laser chip 2 is mounted. Heat is conducted to the cap 5 through the pedestal 15 and the protrusion 16, and can be dissipated from the cap 5. Therefore, even if the heat conduction of the resin member 14 is slightly lowered, there is no problem in dissipating the heat generated from the laser chip 2.
[0022]
Regarding the dimensional accuracy, the degree of contraction of the resin member 14 itself is not constant, and the outer diameter of the stem is set in a hole provided in a mounting board or the like for positioning for dimension setting in the light emitting direction of the laser chip. Insufficient accuracy is obtained for positioning in the xy direction by insertion. However, the cap provided on the outer periphery is made of metal, and the dimensional accuracy can be formed with sufficient accuracy. A stepped skirt is provided on the bottom of the cap with good dimensional accuracy, and the reference surface for positioning the laser chip is fixed to the cap skirt by fixing the inner surface of the step against the protrusion that is integrated with the base. It can be set to the stepped part of the part. Further, since the outer diameter of the skirt portion covering the outer periphery of the stem can be formed with high accuracy, positioning in the xy direction can be formed with sufficient accuracy.
[0023]
When the semiconductor laser having the structure shown in FIG. 1 is fixed to a heat sink made of aluminum with a thickness of 3 mm and a square of 30 mm (the present invention is P1, the conventional structure is Q1), and when not attached to the heat sink (The present invention is P2 and the conventional structure is Q2) The semiconductor laser is operated under the conditions of a forward current I _F = 30 mA, a sampling current I _M = 1.5 mA, and a sampling time T _D = 1 μs. FIG. 3 shows the result of examining the change in the thermal resistance value (R _th ) in comparison with the conventional semiconductor laser. As is clear from FIG. 3, it is clear that there is almost no difference in the effect on heat dissipation by using the resin stem. In FIG. 3, the horizontal axis represents current application time T _p (seconds), and the vertical axis represents thermal resistance R _th (° C./W).
[0024]
【The invention's effect】
As described above, according to the present invention, since the stem is formed of the resin member, it is not necessary to perform special processing, and the stem can be easily manufactured. Moreover, since it is not necessary to attach the lead to glass, the number of parts is reduced and the number of steps is not required. Therefore, a very inexpensive semiconductor laser can be obtained without degrading the electrical and optical characteristics. Furthermore, since the semiconductor laser has the same external shape as that using a conventional metal stem, the conventional product can be replaced as it is.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing the structure of an embodiment of a semiconductor laser of the present invention.
FIG. 2 is an explanatory diagram of a plane and a side surface of the stem portion of FIG.
FIG. 3 is a graph showing the thermal resistance characteristics of the semiconductor laser of FIG. 1 in comparison with the characteristics of a conventional metal stem semiconductor laser.
FIG. 4 is an explanatory view showing a structure of an example of a conventional semiconductor laser.
[Explanation of symbols]
1 Resin stem 2 Laser chip 5 Cap 11 Common lead 12 Lead 13 Lead 14 Resin member 15 Base 16 Protrusion

Claims (4)

And a resin stem having a plurality of leads fixed to the resin portion of the disc-shaped by Rukoto are integrally molded by resin so that a plurality of leads is exposed vertically made of a conductive material, one integral with the plurality of leads is formed on a pedestal you exposed on the resin portion, it is formed so as to be exposed to the pedestal and the resin portion on integrally, extending on the end side of the disc-shaped resin portion from both ends of the pedestal A protruding protrusion, a laser chip fixed to the pedestal, a cap that covers the periphery of the laser chip and has a light transmission window at the top, and abuts against the protrusion and is fixed to the stem A semiconductor laser. 2. The semiconductor laser according to claim 1 , wherein a lead that is not integral with the pedestal among the plurality of leads is fixed by a lead fixing resin different from the pedestal and the resin portion .   3. A stepped skirt portion is formed at the bottom of the cap so as to cover an upper portion and a side portion around the stem, and the skirt portion of the cap serves as a positioning reference surface. Semiconductor laser. 4. The semiconductor laser according to claim 1 , wherein the cap is made of metal, and the cap is fixed to the stem with an adhesive.

Images