JPH10247672A - Optical receiving module - Google Patents

Abstract

(57) [Problem] To provide an optical receiving module having a structure capable of performing an inspection even during a manufacturing process. SOLUTION: A parallel plate capacitor 22 is fixed on a mounting portion 102 of a lead frame, and a photoelectric conversion element 2 for receiving an optical signal and performing photoelectric conversion is mounted on a surface side electrode layer 22b of the parallel plate capacitor 22. You. When the inspection is performed during the manufacturing process, the bonding wire BW ′ is not wired to the power supply line of the lead frame, and another bonding wire B is connected between the photoelectric conversion element 2 and another electronic device 6.
Wire with W. A probe of an appropriate voltage is brought into contact with the surface electrode layer 22b, an appropriate bias is set on the photoelectric conversion element 2 and the electronic device by setting the mounting portion 102 to the ground potential, and a measurement probe is brought into contact with a desired portion. Inspection is carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical receiving module for optical communication, and more particularly to an optical receiving module having a structure in which an electronic device is mounted on a lead frame and sealed with a resin.

[0002]

2. Description of the Related Art In the early days of optical receiving modules, the main purpose was to reduce the size, so that the coaxial type was mainly used. This is because a lens for condensing an optical signal emitted from an optical fiber is arranged in a normal TO type package, and further, an optical axis is provided on the condensing lens for receiving the condensed optical signal. A combined photoelectric conversion element such as a photodiode, and a preamplifier that amplifies a weak electric signal output from the photoelectric conversion element to a voltage level capable of signal processing;
It had a structure with a built-in power supply bypass capacitor and the like. However, this optical receiving module merely has a relatively simple function of converting an optical signal into an electric signal, amplifying and outputting the electric signal.

[0003] In recent years, it has been desired to develop an optical receiving module having a more advanced signal processing function and capable of responding to a demand for miniaturization. As an optical receiving module that can meet such demands, in addition to the photoelectric conversion element, power supply bypass capacitor, and preamplifier, a comparator and a signal processing circuit such as a clock signal restoration circuit are entirely integrated by resin sealing. It is known that a unit having a high function, a small size and an excellent mechanical strength is realized by forming a unit formed and assembling the unit into a module housing.

For example, in this high-performance optical receiving module, a lead frame of a predetermined shape is prepared in a manufacturing process, and a photoelectric conversion element, a preamplifier, and various types of bare chips are mounted on a predetermined mounting portion of the lead frame. After mounting electronic devices such as a signal processing circuit, wiring these electronic devices with each other and between lead pins of a lead frame with a bonding wire, and sealing the whole with a resin through which an optical signal can be transmitted, and then reading the lead. A unit is formed by cutting and removing unnecessary portions of the frame. Then, by aligning the light receiving surface of the photoelectric conversion element in the unit with the optical axis of the sleeve for receiving the ferrule of the optical fiber through the condenser lens, and assembling the module in this state, the height is increased. An optical receiving module that is small in function and excellent in mechanical strength has been formed.

[0005]

However, in a light receiving module in which a photoelectric conversion element and other electronic devices are mounted on such a lead frame and sealed with a resin, the light receiving module is assembled during the manufacturing process. It is not possible to inspect the electronic device for defects due to defects etc.,
Even if it becomes a defective product, there is a problem that an inspection for finding the defective product can be performed only after all the manufacturing processes. Also, naturally, it was not possible to evaluate the characteristics of the electronic device during the manufacturing process.

That is, as shown in FIG. 10, a lead frame in the course of the manufacturing process is connected with a so-called burr (reinforcing portion) in order to prevent a plurality of lead pins from being separated, or a mounting portion for mounting a photoelectric conversion element. A mounting portion for mounting another electronic device is similarly connected by another reinforcing portion (not shown), so that these portions are integrated. For this reason, even after wiring using bonding wires, connecting a power supply to a lead pin from which the reinforcing portion has not yet been removed may cause an electrical short circuit. Could not.

In particular, since the photoelectric conversion element and other electronic devices are sealed with a resin together with each mounting portion, and the reinforcing portion, which is not an object of the resin sealing, is cut and removed, the reinforcing portion is reinforced before the resin sealing. Inspection of the photoelectric conversion element and other electronic devices by removing the portion was substantially impossible.

In FIG. 1, the back surface (the surface opposite to the light receiving surface) of a photoelectric conversion element such as a photodiode also serves as a semiconductor electrode, so that the back surface is mounted on a predetermined mounting portion of the lead frame. The bias of the photoelectric conversion element is set by directly soldering and applying the power supply voltage Vcc to a predetermined power supply voltage application lead pin which is integrally connected to the mounting portion. On the other hand, MOS, bipolar, G
The back surface of another electronic device (for example, a signal processing circuit) manufactured by a semiconductor process such as aAs is directly soldered to another mounting portion, and this mounting portion is set to a ground potential through a ground lead pin. May be operated. However, during the manufacturing process, since these mounting portions are still electrically connected by the reinforcing portion, it is impossible to simultaneously set the photoelectric conversion element and the other electronic device to the normal bias, These electronic devices could not be inspected during the manufacturing process.

[0009] Even if the final product becomes defective, it must be passed through all the manufacturing steps, which is a factor that hinders a reduction in manufacturing cost.

[0010] The present invention has been made in view of such problems, and has as its object to provide an optical receiving module having a structure capable of performing inspection even during a manufacturing process.

[0011]

According to the present invention, there is provided an optical receiving module comprising a photoelectric conversion element for receiving an optical signal and converting the signal into an electric signal on a lead frame. Is mounted on the lead frame via a parallel plate capacitor.

[0012]

The photoelectric conversion element and the lead frame are electrically separated by the interposition of the parallel plate capacitor. Even before the reinforcement portion of the lead frame is removed, inspection and the like are performed with the photoelectric conversion element set to an appropriate bias.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical receiving module according to the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a circuit of an optical receiving module, and FIGS. 2 to 6 show a manufacturing process and a main part structure of a unit in which this circuit is incorporated.

In FIG. 1, a cathode of a photodiode 2 for receiving an optical signal hν is connected to a power supply line Vcc, an anode thereof is connected to an input contact of a preamplifier 6, and further between a cathode and a ground line GND. The power supply bypass capacitor 4 is connected. In the preamplifier 6, a resistor 10 for current / voltage conversion (IV conversion) is connected between the input contact and the inverted output contact. The power supply contact is connected to the power supply line Vcc, and the ground contact is connected to the ground line GND.
Connected to. The inverting output contact and the non-inverting output point of the preamplifier 6 are connected to the inverting input contact and the non-inverting input point of the comparator 16 through the coupling capacitors 12 and 14, respectively, and the power supply contact of the comparator 16 is connected to the power supply line Vcc. , The ground contact is connected to the ground line GND. A power supply bypass capacitor 18 is provided between the power supply contact of the comparator 16 and the ground line GND.
Is connected. The inverted output contact and the non-inverted output point of the comparator 16 are connected to a signal processing circuit 20 such as a clock signal restoring circuit.
The output contact of the signal processing circuit 20 is connected to a predetermined lead pin, or is connected to a signal processing circuit (not shown) at the next stage. The power supply contact of the signal processing circuit 20 is connected to the power supply line V.
cc, a ground contact is connected to the ground line GND, and the power supply contact and the ground line GND
Another power supply bypass capacitor is connected therebetween.

Here, each of the photodiode 2, the power supply bypass capacitors 4 and 8, the preamplifier 6 and the resistor 10, the comparator 16, and the signal processing circuit 20 is a separate semiconductor chip as shown by a dotted line in FIG. (Bear chips) are mounted on a lead frame as they are, and wiring is performed by connecting bonding wires BW and BW ′ to predetermined bonding pads (indicated by □ in the figure) BP formed on each bare chip. In addition, the preamplifier 6 and the resistor 10 are a bare chip made of GaAs semiconductor IC,
Each of the comparator 16 and the signal processing circuit 20 is a bare chip that is made into an IC with a silicon semiconductor.

Then, the optical signal hν is
In is converted into an electric signal is amplified by the preamplifier 6 a signal processable voltage level, by inputting to the comparator 16, the inverted signal Q _B and non from the output contacts of the comparator 16 corresponds to the optical signal hν The inverted signal Q is output, and the signal processing circuit 20 performs signal processing based on these signals Q _B and Q.

Next, the structure of a unit incorporating such a circuit will be described along the manufacturing steps. As shown in FIG.
A lead frame 100 in which a pattern of a predetermined shape corresponding to each unit is continuously formed is prepared, and automatic assembly is performed on a production line. The lead frame 100 is formed of a conductive plate made of a copper plate plated with tin or the like, and a relatively large area mounting portion 102 for mounting a plurality of bare chips such as the photodiode 2 and a plurality of lead pins 104 are reinforced. Are integrated.

A parallel plate capacitor 22 such as a die cap to be the power supply bypass capacitors 4 and 8 is fixed to the center portion of the mounting portion 102 with eutectic solder or the like, and the photodiode 2 is mounted on the parallel plate capacitor 22 with eutectic solder. The photodiode 2 is fixed on the parallel plate capacitor 22 in advance, and the parallel plate capacitor 22 is fixed to the center of the mounting portion 102 by eutectic solder or the like. Furthermore,
The preamplifier 6 is provided near the photodiode 2, the comparator 16 and the signal processing circuit 20 are provided in other portions, and the capacitors 12, 14, and 18 are provided in other predetermined portions of the lead frame 100.
Other passive elements (microchips) are fixed with eutectic solder or the like.

As shown in FIG. 3, the photodiode 2 has n, i, and p ⁺ layers laminated on an n ⁺ semiconductor substrate, and p ⁺
P electrode and SiO ₂ insulating layer is laminated diameter in a predetermined portion of the layer so as to ensure a circular light receiving surface of the tens [mu] m to several hundreds [mu] m, for applying a power supply voltage Vcc to the back surface of the n ⁺ semiconductor substrate A pin-type photoelectric conversion element formed with an n-electrode layer is used. As shown in FIG. 4, the parallel plate capacitor 22 has a metal electrode layer 22a coated on the entire back surface of a thin plate made of a high dielectric material having a thickness of about 150 μm and a length and width of several hundred μm, respectively. Are formed by coating a pair of metal electrode layers 22b and 22c separated from each other, thereby forming two capacitors 4 and 8 having several pF to several tens pF, respectively.

Then, the metal electrode layer 22a of the parallel plate capacitor 22 is directly fixed to the mounting portion 102,
The photodiode 2 and the power supply bypass capacitor 4 shown in FIG. 1 are connected by directly fixing the n-electrode layer of the photodiode 2 to the metal electrode layer 22b on the surface side on which is formed.

After each electronic device is mounted on a predetermined portion of the lead frame 100, a wiring process using a bonding wire is performed. However, the bonding wire BW ′ to be connected between the power supply voltage supply bonding pad provided in each electronic device and the power supply line Vcc of the lead frame 100 is not wired (is kept electrically open). By arranging only the bonding wires BW for the bonding pads for connecting the electronic devices and for the ground line GND,
An inspection is performed during the manufacturing process.

That is, the potential of the lead frame 100 is set to the ground potential of the power supply for measurement, and the tip of the probe set to the power supply voltage Vcc of the power supply for measurement is bonded to the power supply voltage of each electronic device. By making contact with the pad, a bias equivalent to the circuit shown in FIG. 1 is set, and the inspection is performed by bringing the short hand for measurement connected to the measuring instrument into contact with a desired portion of each electronic device.

More specifically, when a short hand set to the power supply voltage Vcc is brought into contact with the metal electrode layers 22b and 22c of the parallel plate capacitor 22, the power supply voltage is directly applied to the back side (anode side) of the photodiode 2. Vcc is applied, and the preamplifier 6 has a bonding wire BW
The power supply voltage Vcc is applied through the switch. At this time, since the photodiode 2 and the lead frame 100 are electrically separated by the parallel plate capacitor 22, it is possible to apply an appropriate power supply voltage Vcc to the photodiode 2 even when the lead frame 100 is at the ground potential. it can.

Therefore, in the prior art, since the photodiode is directly attached to the lead frame, the reinforcing portion of the lead frame is removed to electrically connect the photodiode mounting portion and other electronic device mounting portions. In this embodiment, the photodiode 2 and other electronic devices 6, 16, and 20 are mounted on the same mounting portion 102, and the inspection can be performed only after the separation. Even if the bias setting conditions for operating the diode 2 and the other electronic devices 6, 16, and 20 are different, these electronic devices can be set to an appropriate bias. Inspection can be performed.

Next, when the inspection during the manufacturing process is completed, the short hand is removed, and the bonding pad BP for applying the power supply voltage and the lead pin for applying the power supply of the lead frame 100 are connected with the bonding wire BW '. The individual units are completed by carrying the resin into a mold, sealing the portion within the range shown by the dotted line in FIG. 2 with a resin, and cutting and removing the reinforcing portion and unnecessary portions of the lead frame 100. . The resin used is a cured resin transparent to the optical signal hν. Further, when a defective portion is found in the inspection, a subsequent manufacturing process for the corresponding unit is omitted, and a sorting process such as continuing only manufacturing for a normal unit is performed.

Then, only for the completed normal unit, the photodiode 2 is connected to the sleeve for receiving the ferrule of the optical fiber via the condenser lens.
By aligning the light receiving surfaces of the light receiving surfaces with the optical axis and assembling the light receiving surfaces in the module housing in that state, a light receiving module having high performance, small size and excellent mechanical strength is completed.

Although the case in which the lead frame 100 and each electronic device are simply sealed with a resin using the above-described mold has been described, when the resin is sealed, the sleeve and the condenser lens are also attached to the light receiving surface of the photodiode 2. , And can be integrally formed of resin.

The connection between the back surface of the photodiode 2 and the front side electrode layer 22b of the parallel plate capacitor 22, the back surface 22a of the parallel plate capacitor 22 and the lead frame 100
Although the case where eutectic solder is used to connect the preamplifier 6, the comparator 16, and the signal processing circuit 20 to the lead frame 100 has been described, the present invention is not limited to such a connection structure, and a conductive resin (adhesive) may be used. Or by a conductive adhesive sheet.

Although the case where the pin type photoelectric conversion element shown in FIG. 3 is used has been described, the present invention is not limited to the photoelectric conversion element having such a structure. For example, in a photoelectric conversion element using a semi-insulating substrate as shown in FIG.
As shown in FIG. 6, the photoelectric conversion element is directly mounted on one surface side metal layer 22b of the parallel plate capacitor 22, and the p-side electrode provided on the surface side of the photoelectric conversion element is bonded to the surface side metal layer by wire bonding. Layer 22b and another boding wire B between the output contact and the input contact of the preamplifier.
By connecting with W ", it is possible to realize a structure that can be inspected during the manufacturing process.

The structure in which the photodiode 2, the parallel plate capacitor 22, the preamplifier 6, the comparator 16, and the signal processing circuit 20 are mounted on one mounting portion 102 and sealed with resin has been described. The present invention is not limited to this. For example, a first mounting unit for mounting the photodiode 2, the parallel plate capacitor 22, and the preamplifier 6, and a second mounting unit for mounting the comparator 16 and the signal processing circuit 20 Alternatively, the above components may be mounted on the respective mounting portions by using a lead frame having a shape separated from the other portions, and then resin-sealed collectively. It is not preferable that the photodiode 2 and the preamplifier 6 are separately mounted on separate mounting portions, because this may increase noise components.

Next, another embodiment will be described with reference to FIGS. 7 shows another example of a circuit mounted on the optical receiving module, FIG. 8 shows a waveform diagram for explaining the operation of the circuit, and FIG. 9 shows a main structure of a unit in which this circuit is incorporated. In FIG. 7, the same or corresponding parts as those in FIG. 1 are indicated by the same reference numerals.

FIG. 7 is different from the circuit of FIG. 1 in that two preamplifiers 6 composed of inverting amplifiers having the same characteristics and provided with resistances 10a and 10b for IV conversion are provided.
a, 6b, and these preamplifiers 6a, 6b and resistors 10a, 10b are mounted on a lead frame as bare ICs made of GaAs semiconductors. A dummy capacitor 24 having a value equal to the junction capacitance between the anode and the cathode of the photodiode 2 is connected between the anode and the input contact of the preamplifier 6a, connected between the cathode and the input contact of the preamplifier 6b, The output contact of each preamplifier 6a, 6b is a coupling capacitor 4
2 and 44 are connected to the input contact of the comparator 16.

Then, the optical signal hν is
, And is amplified to a voltage level that can be processed by the preamplifier 6b. The AC component is input to the non-inverting input terminal of the comparator 16 via the coupling capacitor 44. The preamplifier 6a amplifies the voltage generated in the dummy capacitor 24, and inputs the AC component to the inverting input contact of the comparator 16. Here, since the dummy capacitor 24 is set to a value equal to the junction capacitance of the photodiode 2, when a voltage fluctuation occurs in the power supply line Vcc, an optical signal component is superimposed on this voltage fluctuation component in the preamplifier 6b. Signal will be input,
A voltage variation component equal to that of the photodiode 2 is input to one preamplifier 6a, and a signal including a voltage variation component as shown in FIG. 8A is output from each of the preamplifiers 6a and 6b. Is output. The AC components of these output signals are input to the comparator 16 through the coupling capacitors 42 and 44, and by comparing the voltage levels of the respective AC components, the voltage fluctuation components are substantially canceled, and FIG. non-inverted signal Q and an inverted signal Q _B corresponding only to the optical signal hν shown is output. As described above, this circuit is configured to exhibit a noise suppressing effect on the power supply line Vcc by providing the dummy capacitor 24 having a value equal to the junction capacitance of the photodiode 2.

In the manufacturing process of a unit incorporating such a circuit, a lead frame 100 similar to that shown in FIG.
As shown in FIG. 9, a parallel plate capacitor 22 is fixed to the center of the mounting portion 102 by eutectic solder or the like, and a photodiode is provided on the metal electrode layer 22b of one capacitor 4 of the parallel plate capacitor 22. The second n-electrode layer and one terminal 24a of the dummy capacitor 24 are fixed by eutectic solder or the like. Further, a bare chip having preamplifiers 6a and 6b and resistors 10a and 10b formed near the photodiode 2, a bare chip of the comparator 16 and the signal processing circuit 20 in another part, and a capacitor 12 in another predetermined part of the lead frame. , 14, 18 and other passive elements (microchips) are fixed by eutectic solder or the like.

A bonding wire BW 'for connecting a power supply voltage supply bonding pad provided on these electronic devices to a power supply line Vcc of the lead frame 100 is not provided, but a connection between each electronic device is made. By laying only the bonding wires BW between the bonding pads for connection and the ground line GND, an inspection is performed during the manufacturing process.

That is, a short hand set to the power supply voltage Vcc is brought into contact with the metal electrode layers 22b and 22c of the parallel plate capacitor 22 so that the back side (anode side) of the photodiode 2 and one end 24a of the dummy capacitor 24 can be properly fitted. And the pre-amplifiers 6a, 6a
b, an appropriate power supply voltage Vcc is applied via a bonding wire BW, and the other end 24b of the dummy capacitor 24 and the input contact of the preamplifier 6a, the cathode of the photodiode 2 and the input contact of the preamplifier 6b are bonded to the bonding wire. B
Connect with W. At this time, the photodiode 2 and the dummy capacitor 24 are electrically separated from the lead frame 100 by the parallel plate capacitor 22, so that even if the lead frame 100 is at the ground potential, the photodiode 2 and the dummy capacitor Power supply voltage V
cc can be applied, and an inspection can be performed during the manufacturing process.

Next, when the inspection in the middle of the manufacturing process is completed, the short hand is removed and the bonding pad BP for applying the power supply voltage and the lead pin for applying the power supply of the lead frame 100 are connected with the bonding wire BW '. Each unit is completed by transporting it into a mold and sealing it with a resin, and further cutting and removing a reinforcing portion and an unnecessary portion of the lead frame 100. The resin is the optical signal hν
, A transparent cured resin is used. Further, when a defective portion is found in the inspection, a subsequent manufacturing process for the corresponding unit is omitted, and a sorting process such as continuing only manufacturing for a normal unit is performed. And only about the completed normal unit,
By aligning the light receiving surface of the photodiode 2 with the optical axis via the condenser lens with respect to the sleeve for receiving the ferrule of the optical fiber, and assembling the module with the module in that state, a high-performance, compact and mechanical To complete an optical receiving module with excellent mechanical strength.

As described above, according to these embodiments, since the photoelectric conversion element is mounted on the lead frame via the parallel plate capacitor, the electrical connection to the lead frame is made during the manufacturing process. In this state, the inspection can be performed by setting the photoelectric conversion element to an appropriate bias. In addition, this parallel plate capacitor not only electrically separates the photoelectric conversion element from the lead frame, but also performs a predetermined wiring with a bonding wire so that a power supply bypass between the photoelectric conversion element and the preamplifier can be achieved. The effect that it can be used for a capacitor is obtained.

[0039]

As described above, according to the present invention, an appropriate power supply voltage is applied to the photoelectric conversion element even during the manufacturing process before the reinforcing portion of the lead frame is cut and separated. Inspection can be performed. The manufacturing cost can be reduced by performing a sorting process such as omitting a manufacturing process for a defective product and continuing to manufacture only a normal product.

Further, there can be obtained such an effect that a parallel plate capacitor for mounting the photoelectric conversion element can be used as a power supply bypass capacitor of the photoelectric conversion element and other electronic devices.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a circuit mounted on an optical receiving module.

FIG. 2 is an explanatory view showing a shape of a lead frame.

FIG. 3 is an explanatory diagram illustrating a structure of an example of a photoelectric conversion element.

FIG. 4 is an explanatory diagram for explaining a connection structure of a parallel plate capacitor, a photoelectric conversion element, and a lead frame.

FIG. 5 is an explanatory diagram showing a structure of another photoelectric conversion element.

FIG. 6 is an explanatory diagram for explaining a connection structure between a parallel plate capacitor, another photoelectric conversion element, and a lead frame.

FIG. 7 is a circuit diagram showing another example of a circuit mounted on the optical receiving module.

FIG. 8 is a waveform chart for explaining the operation of another circuit.

FIG. 9 is an explanatory diagram for explaining a connection structure of a parallel plate capacitor, a photoelectric conversion element, and a lead frame in another circuit.

FIG. 10 is an explanatory diagram showing a structure of a conventional optical receiving module.

[Explanation of symbols]

2: photoelectric conversion element, 4, 8, 18: power supply bypass capacitor, 6, 6a, 6b: preamplifier, 10, 10a, 1
0b: resistor, 12, 14, 42, 44: coupling capacitor, 16: comparator, 20: signal processing circuit,
24: dummy capacitor, 100: lead frame, 1
02 mounting part, 104 lead pin, BP bonding pad, BW, BW ', BW "bonding wire.

Claims (4)

[Claims] 1. A light receiving module comprising a photoelectric conversion element for receiving an optical signal and converting it into an electric signal on a lead frame, wherein the photoelectric conversion element is mounted on the lead frame via a parallel plate capacitor. An optical receiving module, comprising: 2. The optical receiving module according to claim 1, wherein the parallel plate capacitor is a power supply bypass capacitor of the photoelectric conversion element. 3. A preamplifier for amplifying an electric signal converted by the photoelectric conversion element, wherein an output of the photoelectric conversion element and an input of the preamplifier are connected by a bonding wire. Item 2. The optical receiving module according to item 1. 4. A preamplifier for amplifying an electric signal converted by the photoelectric conversion element, wherein an output of the photoelectric conversion element and an input of the preamplifier are connected by a bonding wire, and the parallel plate capacitor comprises: The optical receiving module according to claim 1, wherein the optical receiving module is a power supply bypass capacitor of the preamplifier.