A conventional semiconductor laser of stem type that is used as a pickup for a CD has such a structure as illustrated in FIG. 8. More particularly, a stem 20 is used that is formed by cold forging a metallic material such as iron for forming a heat sink portion 22 by raising remote of a central portion of a base 21 and by fixing leads 23, 25 therein by means of glass 26 or similar; a laser chip 31 is mounted onto this heat sink portion 22 through a sub-mount 34 comprised of a silicon substrate or the like; one electrode (rear surface of the chip 31) is electrically connected to the lead 23 through a wire 33 via are lay portion 38 of the sub-mount 34 while the other electrode is connected to the sub-mount 34 through a wire 33 to be electrically connected to a common lead 24 through the heat sink portion 22 and the base 21 via a rear surface of the sub-mount 34.
It should be noted that 32 denotes alight receiving element for monitoring, wherein one electrode is electrically connected to the lead 25 via the wire 33 while the other electrode is electrically connected to the common lead 24 via the sub-mount 34, the heat sink portion 22 and the base 21. A cap 35 is finally covered onto the periphery thereof. A throughhole 35a is provided at a central portion of a top portion of the cap 35 such that light emitted by the laser chip 31 may pass through, and a glass plate 36 is sealed thereon by means of an adhesive 37.
Despite of the fact that the heat sink portion 22 needs to be formed between the leads 23 and 25 in this structure, it is necessary to seal the leads 23, 25 by glass 26 so that the radius of the stem 20 can not be reduced. This is the reason why figurations of conventional stems could be reduced up to approximately 5.6 mmφ only.
On the other hand, demands for extremely thinning in recent pickups for CDs and DVDs are increasing accompanying light and compact structure of electronic devices as represented by notebook type personal computers. As for pickups, semiconductor lasers of small outer diameter are being required which are used in horizontally turned conditions, wherein it is desirable to set the outer diameter to not more than approximately 3.5 mmφ, and it has been developed for semiconductor lasers that are arranged in that, as illustrated in FIG. 9, a stem 20 is formed by performing deep drawing of a plate-like body for integrally forming a ring 27 and a seating portion 28 that performs the function of the heat sink, wherein leads 23, 25 are directly sealed into the ring 27 through glass 29 or the like, and a cap 35 is covered onto the outer periphery of the stem 20 through press-fitting (for instance, U.S. Pat. No. 5,878,069). By employing such a structure, the heat sink needs not be directly formed onto the base of the stem, and since no space for welding the cap is required, it is possible to achieve a structure having an outer diameter of approximately 3.3 mmφ. It should be noted that portions that are identical to those of FIG. 8 are marked with the same reference numerals, and explanations thereof will be omitted.
However, since the heat sink 22 is formed between the leads 23, 25 in such a structure, the heat sink will necessarily be reduced in size accompanying the downsizing. In laser chips for CDs having a small chip size of approximately 0.25 mm by 0.25 mm square and having a small operating current, it would not mind even if the shape of the heat sink becomes small, but in laser chips for DVDs having a large chip size of approximately 0.25 mm by 0.5 mm square and having a large heat generating, insufficient radiation resulted in a drawback of lack of light emission of the laser chip.
The inventors of the present invention have thus developed a semiconductor laser that satisfies the requirements for downsizing of the entire package without degrading the heat radiation properties upon securing a size for the heat sink that is equivalent to that of above-described heat sink of stem type as illustrated in FIG. 8 (for instance, Japanese Patent Laid-Open Publication No. 2001-111152; U.S. application Ser. No. 09/684,954). That is, as illustrated in FIG. 10, a heat sink 22, which is provided on one surface side of a base 21 into which at least two leads 23, 25 are fixed as to project to both sides, includes a supporting portion 22a that is fixedly attached to the base and a mounting portion for the laser chip, having a different shape from the supporting portion 22a and the heat sink 22 (mounting portion) is formed to extend to the side of the two leads 23, 25. By employing such an arrangement, it is possible to form the laser chip mounting surface to be of broad width to thus improve the heat radiation properties and to narrow the distance between the leads 23, 25. The diameter of the stem 20 may be accordingly made smaller and it is possible to mount a laser chip for a DVD also when its size is approximately 3.3 mmφ. It should be noted that portions that are identical to those of FIG. 8 are marked with the same reference numerals and explanations thereof will be omitted.
While DVDs are being equipped in notebook type personal computers as standard items accompanying thinning of pickups for DVDs and the like, it is also being wanted for low cost manufacture of pickups and semiconductor lasers in accordance with reductions in prices of notebook type personal computers. However, a conventional structure in which both of downsizing and favorable heat radiation properties have been secured is a structure in which the heat sink and the leads (including glass portions for fixedly attaching the leads) are overlapping (overhanging) when seen on a plan view, so that the heat sink is often composed of two parts or even if the heat sink is of single structure, drawbacks are presented in that manufacturing processes become complicated due to a complicated shape of such a part or in that manufacturing cost is increased even if the structure is of single structure.
Through recent developments in recording media markets, CD-R/RWs are rapidly becoming popular, and they are being on the trend of being equipped as standard items in personal computers, similar to DVDs. Since a semiconductor laser of high output is used as a laser for CD-R/RWs, the laser chip has a size of 0.25 mm by 0.8 mm square that is larger than that of a laser chip for DVDs for the purpose of achieving high output, and it also has an operating current that is four to five times larger than that for CDs. Accordingly there is a problem that a desired optical output can not be achieved if the dispersion of heat of a semiconductor laser chip is not enough when downsizing of a semiconductor laser of high output.