JPH04349686A - Chip carrier - Google Patents

Abstract

PURPOSE:To provide a chip carrier which is excellent in high-speed responsiveness and is capable of preventing high-speed modulation signal from deteriorating in waveform, mounting in high-density, attaining a sufficient cooling capacity in the case of mounting on a thermoelectronic cooling device, and preventing a photosemiconductor device from being out of optical axis. CONSTITUTION:A chip carrier keeps a base 2 loaded with a flexible board 15 which has a small thermal conductivity, high flexibility, and carries transmission lines of matched impedance.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip carrier for mounting optical semiconductor elements.

0002

2. Description of the Related Art In recent years, as transmission speeds and processing speeds in optical communications and optical information processing have increased, high-speed response characteristics of optical semiconductor devices have become important. In order to achieve high-speed response characteristics, it is necessary not only for the element itself to be high-speed, but also to implement an element suitable for high-speed response.

A chip carrier for mounting semiconductor elements is the simplest type of package provided with an area for mounting an optical semiconductor element and electrode pads connected to electrodes of the optical semiconductor element by wire bonding or the like. Optical semiconductor devices mounted on chip carriers are easy to combine with other optical semiconductor devices and integrated circuit devices, and have a high degree of freedom in designing optical coupling systems with optical fibers, etc., so they are used for a variety of purposes. There is.

FIG. 7 shows an example of a conventionally used chip carrier in which a laser diode chip is mounted as an optical semiconductor element.

In FIG. 7, a laser diode 1 is fixed by solder onto a heat sink 3 fixed on a metal base 2. As shown in FIG. Heat sink 3 is laser diode 1
This is a buffering member that efficiently dissipates the heat generated by the laser diode 1 and the base 2 to the base 2, and at the same time absorbs the difference in thermal expansion between the laser diode 1 and the base 2. The electrodes of the laser diode 1 are connected by metal wires 4 directly to the base 2 on the anode side and to the electrode pads 5 on the heat sink 3 on the cathode side. The electrode pad 5 is made of ceramic and is electrically insulated from the base 2. A metal lead 6 is provided on the electrode pad 5 for connection to an external circuit.

[0006] If such a chip carrier is used,
The laser diode 1 can be modulated by connecting the leads 6 and the base 2 as electrodes to an external drive circuit. However, when the modulation speed is as high as several hundred MHz or more, high-speed modulation becomes difficult due to the influence of parasitic impedance due to mounting, no matter how excellent the laser diode 1 has high-speed response characteristics. FIG. 8 shows an equivalent circuit when the laser diode 1 is modulated using the chip carrier shown in FIG. LL and CC in FIG. 8 are the parasitic inductance of the lead 6 and the parasitic capacitance of the electrode pad 5, respectively. Due to the structure of the chip carrier, it is physically difficult to reduce these parasitic inductances and capacitances to a negligible level, and when transmitting high-speed modulation signals of several hundred MHz or more, waveform deterioration may occur. Therefore, there was a limit to the speed that could be modulated.

[0007] Furthermore, in the case where an IC-based drive circuit is mounted on the same chip carrier, it is necessary to provide a necessary number of leads on the electrode pads 5. Since these leads are mechanically fixed onto the electrode pads, there is a limit to miniaturization due to processing problems, making high-density packaging difficult.

Further, the laser diode 1 may be used with its temperature controlled using a thermoelectric cooling element. FIG. 9 shows a cross-sectional view of a laser diode module with a built-in thermoelectric cooling element using a conventional chip carrier. The base 2 is fixed onto a second base 8 with screws or the like, and mounted on a thermoelectric cooling element 9. The optical axis of the optical fiber 10 is aligned with the laser diode 1, and the core portion is fixed onto the second base 8 by soldering. Furthermore, 11 is a package,
In addition to accommodating a chip carrier and a thermoelectric cooling element 9,
A signal input terminal 12 connected to the optical fiber 10 and the lead 6 of the chip carrier is fixed with sufficient mechanical strength. In such a configuration, even if the temperature of the chip carrier portion is controlled to be, for example, 25 degrees Celsius by the thermoelectric cooling element 9, if the environmental temperature outside the package 11 is as high as, for example, 80 degrees Celsius, the external heat flows through the leads 6 of the chip carrier so that the thermoelectric cooling element 9
must be driven with a large amount of electric power to cool it down, which has the disadvantage that sufficient cooling capacity cannot be obtained when the temperature difference is large. Furthermore, since thermal stress due to thermal expansion of the package is applied to the chip carrier through the leads 6, there is a drawback that the optical axis of the laser diode 1 is shifted and the optical output from the optical fiber 10 fluctuates.

[0009]

As described above, in conventional chip carriers, it has been difficult to achieve sufficient high-speed response characteristics and high-density packaging due to parasitic impedance caused by leads and insulating members. Furthermore, when the chip carrier is mounted on a thermoelectric cooling element, sufficient cooling capacity cannot be obtained when the external temperature is high, which also causes the problem of optical axis misalignment of the laser diode.

The present invention has been made to solve the above-mentioned problems, and is capable of high-density mounting without deteriorating high-speed response characteristics due to parasitic impedance, and has sufficient performance when mounted on a thermoelectric cooling element. It is an object of the present invention to provide a chip carrier that has a cooling capacity and does not cause optical axis deviation of an optical semiconductor element. [Structure of the invention]

[0011]

[Means for Solving the Problems] In order to solve the above problems, the chip carrier of the present invention includes a base on which an optical semiconductor element or an integrated circuit element is mounted in addition to the optical semiconductor element, and a base on which an optical semiconductor element or an integrated circuit element is placed in addition to the optical semiconductor element. The flexible wiring board is characterized by comprising: a flexible wiring board placed on a metal conductor layer and a connecting means for electrically connecting the optical semiconductor element or integrated circuit element to the flexible wiring board; It is characterized by forming an impedance-matched transmission line made of an insulating layer.

0012

[Function] In the chip carrier with the above configuration, a flexible substrate is provided on the base on which the optical semiconductor element is mounted, and a transmission line is formed on this flexible substrate, so that impedance matching is achieved when connected to an external circuit. easily done,
Since it is not affected by parasitic impedance, waveform deterioration of the high frequency signal does not occur. Further, since the wiring pattern of the lines on the flexible substrate can be microfabricated, the mounting area can be reduced even if a plurality of wirings are required.

Furthermore, since the flexible substrate has high thermal resistance, it is possible to reduce heat transmitted from the outside to the optical semiconductor element. Furthermore, the flexibility of the flexible substrate allows it to absorb stress applied from the outside.

[0014]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of a chip carrier for an optical semiconductor device according to the present invention. The chip carrier shown in Figure 1 has an external circuit (not shown) and a laser diode 1.
A flexible substrate 15 is used for connection. A microstrip line 14 is formed as a transmission line on this flexible substrate 15 and is fixed to a metal base 2. For example, as shown in FIG. 2, the flexible substrate 15 is formed of an insulating layer A made of polyimide and conductor layers B and C made of copper, and the line pattern of the conductor layer B above the insulating layer A is microfabricated by etching. It is something that

Returning to FIG. 1, reference numeral 13 denotes an impedance matching resistor that terminates the circuit. The electrodes of a laser diode 1 fixed on a base 2 via a heat sink 3 are connected to a microstrip line 14 on one side and an impedance matching resistor 13 on the other side with a metal wire 4. This metal wire 4 is bonded, for example, by a wire bonding method, and has a diameter of about 10 to 100 μm.

FIG. 3 shows an equivalent circuit when the laser diode 1 is modulated using the chip carrier having the above structure. In the circuit of FIG. 3, when modulating the laser diode (LD) with a high frequency signal of several hundred MHz output from the drive circuit, the characteristic impedance of the microstrip line 14 and the impedance matching resistor are set to a predetermined value (
For example, if it is set to 50Ω), a high frequency signal can be applied to the laser diode without waveform deterioration. The impedance of the microstrip line 14 can be set by changing the thickness h of the insulating layer A of the flexible substrate 15 shown in FIG. 2, the width w of the line pattern, the thickness t, the specific conductivity of the insulator, the type of metal, etc. It's easy to do. Therefore, waveform deterioration due to parasitic impedance, which conventionally occurs, does not occur, and a chip carrier with excellent high-speed response can be realized.

By the way, in the flexible substrate, the conductor layer with high thermal conductivity can be made as thin as several tens of microns, and the insulating layer can be made thinner than the conductor layer, depending on the value of characteristic impedance.
Thermal conductivity is orders of magnitude lower. Package 1 shown in FIG. 9 is obtained by mounting the above-mentioned chip carrier on a thermoelectric cooling element.
1, the package and the optical semiconductor element can be connected with high thermal resistance. That is, for the temperature of the chip carrier whose temperature is controlled by the thermoelectric cooling element,
Even when the environmental temperature around the package is high, the thermal resistance of the flexible substrate is high, so the flow of heat from the package can be sufficiently reduced. Thereby, sufficient cooling capacity can be obtained without driving the thermoelectric cooling element with unnecessarily large power.

Further, the flexible substrate 15 can absorb stress caused by thermal expansion of the package 11 shown in FIG. 9 due to its flexibility. When the environmental temperature around the package 11 increases, the package 11 thermally expands, for example, expanding vertically and horizontally. Along with this, package 1
Stress such as tension occurs on the flexible board connected to 1, but since the flexible board is flexible, the stress can be reduced by allowing the flexible board to slacken slightly in advance to account for this stress. Even if it occurs, it can be absorbed. As a result, the optical axis of the laser diode 1 is not shifted due to stress generation, and stable output from the optical fiber can be obtained.

Next, a second embodiment will be explained with reference to FIG. This embodiment differs from the first embodiment in that each electrode of the laser diode 1 is connected to two microstrip lines 14 with a metal wire 4. With this configuration, the circuit can be terminated using an impedance matching resistor (not shown) in the package that houses the chip carrier, rather than on the chip carrier, thereby reducing the adverse effects caused by the heat generated by the resistor being transmitted to the laser diode 1. can be prevented.

Next, a third embodiment will be explained with reference to FIG. FIG. 5 shows an example in which, in addition to the optical semiconductor element, a laser diode drive circuit 16, which is an integrated circuit element for driving the optical semiconductor element, is also mounted on the chip carrier. Since the signal source (not shown) and the integrated circuit element 16 are connected by the impedance-matched microstrip line 14, the high frequency signal output from the signal source is input to the integrated circuit element without waveform deterioration. . In order to use an integrated circuit element, a plurality of lines 17 such as a power supply line and a bias adjustment line are required in addition to the signal line. Flexible board 15
The wiring pattern is formed by etching, etc., so it is possible to process the line width and line spacing to about 100 μm, and even if multiple wiring is required, the area required for mounting can be reduced, which was previously difficult to achieve. This enables high-density packaging.

Next, a fourth embodiment will be explained. Figure 6
is a back-illuminated photodiode 18 as an optical semiconductor element.
, is a diagram illustrating a fourth embodiment in which, for example, an amplifier circuit element 19 capable of current/voltage conversion is used as an integrated circuit element. In this example, the photodiode 18 and the amplifier circuit element 19, which is an integrated circuit element, are electrically connected to the flexible substrate 15 by a flip-chip mounting method using bumps 20. The bumps 20 can be made of solder, gold, alloy, or the like. According to this configuration, the high frequency output signal from the integrated circuit element is connected to the next stage electronic circuit (not shown) through the impedance-matched microstrip line 14, so that the high frequency output signal can be connected without causing any waveform deterioration. be able to. Also, similar to the third embodiment, high-density packaging is possible.

[0023]

[Effects of the Invention] As described above, the chip carrier of the present invention has excellent high-speed response, can prevent waveform deterioration of high-speed modulation signals, can be mounted at high density, and can be mounted on a thermionic cooling element. In this case, sufficient cooling capacity can be obtained and optical axis deviation of the optical semiconductor element can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a flexible substrate used in the present invention.

FIG. 3 is a diagram showing an equivalent circuit during laser diode modulation.

FIG. 4 is a diagram showing a second embodiment of the present invention.

FIG. 5 is a diagram showing a third embodiment of the present invention.

FIG. 6 is a diagram showing a fourth embodiment of the present invention.

FIG. 7 is a diagram showing a conventional chip carrier.

FIG. 8 is a diagram showing an equivalent circuit when a laser diode is modulated using a conventional chip carrier.

FIG. 9 is a diagram showing a laser diode module using a conventional chip carrier.

[Explanation of symbols]

Claims (9)

[Claims] 1. A base comprising a base on which an optical semiconductor element is placed, a flexible substrate placed on the base, and connection means for electrically connecting the optical semiconductor element and the flexible substrate. A chip carrier characterized by: 2. The chip carrier according to claim 1, wherein the connecting means is a metal wire. 3. The chip carrier according to claim 1, wherein the connecting means is a bump. 4. A base on which an optical semiconductor element and an integrated circuit element are placed, and a flexible substrate placed on the base and on which a plurality of lines are formed, wherein the optical semiconductor element and the integrated circuit element are placed on a flexible substrate. A chip carrier, wherein the element, the integrated circuit element, and the flexible substrate are electrically connected by a connecting means. 5. The chip carrier according to claim 1, wherein the flexible substrate is made of a metal conductor layer and a polyimide insulating layer, and has an impedance-matched transmission line formed thereon. 6. The chip carrier according to claim 4, wherein the connecting means for connecting the optical semiconductor element and the integrated circuit element is a metal wire. 7. The chip carrier according to claim 4, wherein the connection means for connecting the optical semiconductor element and the integrated circuit element is a bump. 8. The chip carrier according to claim 4, wherein the connecting means for connecting the integrated circuit element and the flexible substrate is a metal wire. 9. The chip carrier according to claim 4, wherein the connecting means for connecting the integrated circuit element and the flexible substrate is a bump.