Laser module package processes .1 Material prepared

(a) Chip Resistor: A commercial chip resistor was designed to be used for microwave and high-speed optical communication applications [3.1]. In order to reduce the parasitic capacitance to ground, this chip resistor was fabricated on a ceramic (Al2O3) substrate by thin film technology. The dimensions of the chip resistor was 12 (Width) x 15 (Length) x 10 (Thickness) mils, as shown in Fig. 3.1. Based on the specifications of the chip resistor, the value of resistor and capacitance were about 1 Kohm and 0.024 µF, respectively. The RC time constant was 2.4 x 10^-11 sec. The operating frequency was suitable for achieving to 20GHz.

Fig. 3.1: The schematic diagram of the chip resistor.

(b) Resistor Submount: The resistor submount was also made of ceramic material (Al2O3), as shown in Fig. 3.2. The dimensions of the resistor submount were 0.50 x 0.40 x

0.25mm

0.30mm

0.38mm

Bonding pad

Ceramic substrate

0.13 mm. It was used to adjust the height of the resistor submount.

Fig. 3.2: The schematic diagram of the resistor submount.

(c) LD Submount: The laser diode was deposited on the LD submount for easy adjusting the bonding position. The dimensions of the LD submount made of ceramic material were 0.6 x 0.4 x 0.24 mm as shown in Fig. 3.3. The laser diode was deposited on the top-side of the solder pad by die-bonding technology. The back-side solder pad was deposited on the TO-56 header. The bonding pad was used for wire bonding connection and was electrical short with the cathode of the laser diode. In order to deposit the LD on the center of the TO-56 header, the thickness of the submount should be carefully consideration.

(a) (b)

Fig. 3.3: The schematic diagram of the LD submount at (a) the view of top-side and (b) back-side.

Solder pad (AuSn) 0.24 mm

0.40 mm

0.60 mm

Bonding pad (Ti/Pt/Au)

Ceramic substrate 0.40mm

0.50mm 0.13mm

(b) Ball Lens Cap: The ball lens cap was used to protect the device on the TO-56 header and focus the laser beam output from the laser diode. The ball lens was integrated with the metal can by the material of PbO. The material of PbO has the property of low melting point (600^oC~640^oC) and was easy to joint with the metal. The surface of the ball lens was fabricated an AR coating with transmittance of 98% for 1300nm. For the reliability consideration, the characteristic of the hermetically sealed have to keep below 1 x 10^-4 Pa‧m³/sec [3.2].

(a) (b)

Fig. 3.4: The schematic diagram of the ball lens cap.

3.1.2 Die-Bonder System

The laser diode and the LD submount were bonded on the stem of the TO-56 header by die-bonding technology. The die-bonder system (Omni Bonder-Model 860, Semiconductor Equipment Corp.) could deposit the device onto the target position with a high accuracy adjustment, as shown in Fig. 3.5.

The die-bonder system was consisted of:

(a) Viewer System: A CCD camera, a monitor, an optics system with 50% beam splitter with 45^o, two light sources, as shown in Fig. 3.6(a). The viewer system can help us to view the position of the bond head and the device on the die stage at the same time. It also can view the position of the bond head and the bonding position on the working stage at the same time.

Ball lens (BK7)

Metal can (NiFe)

4.2mm φ=1.5 or 2.0mm

Fig. 3.5: Photo of the die-bonder system.

(a) (b)

Fig. 3.6: Photo of (a) the viewer system and (b) the dual bond head.

(b) Dual Bond Head: One bond head was used for laser diode, and another one was used for submount or solders material, as shown in Fig. 3.6(b). The bond head of the laser diode had a heater and a thermocouple for preheating the sample. This dual bond head would hold the sample from the die stage by a vacuum tip.

(c) Die Stage: The laser diode, solder materials, or other samples was placed on a carrier glass and hold on the die stage, as shown in Fig. 3.7(a). The carrier glass was hold by a vacuum.

CCD Monitor

Movable table Die stage Bond head

Work stage Viewer System

For laser diode For submount CCD camera

Viewer Bond head

Die stage

(a) (b)

Fig. 3.7: Photo of the (a) die stage, and (b) the work stage.

(d) Work Stage: The work stage has a heating stage and a X-, Y-, ψ- micrometer, as shown in Fig. 3.7(b). The TO-56 header was fixed at the heating area. The X-, Y-micrometer can help us to fine adjust the bonding position with resolution of 1µm.

(e) Movable Table: The die and work stage were placed on the movable table. It can move these two stages below the dual bond head.

Because the die-bonder system is a semi-automatic operation, we should set proper bonding parameters. Table 3.1 shows the parameter of the dual bond heads. The pick load was the bond head’s stress over the device as the device was held up. The parameter of the bond load was the stress of the bond head over the device as the device was bonded. The temperature of the bond head was acceptable to set from 80~120^oC.

Table 3.1: The parameters of the dual bond heads.

Parameter Unit Value Max.

Pick load g 5~10 200

Bond load g 15~25 200

Tip Temp. ^oC 80~120 250

The working stage will always be stable keep at the idle temperature, before the bonding procedure. As starting the bonding procedures, the temperature of the working stage will Carrier glass

Vacuum

X-axis micrometer