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MOTOROLA

SEMICONDUCTOR TECHNICAL DATA

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I F , INSTANTANEOUS FORWARD CURRENT (AMPS)

100

10

1.0TJ = 100°C

Figure 1. Typical Forward Voltage

Figure 2. Maximum Forward Voltage

C, CAPACITANCE (pF)

100,000

TJ = 25°C

10,000

VR, REVERSE VOLTAGE (VOLTS)

Surface mount board layout is a critical portion of the total design. The footprint for the semiconductor packages must be the correct size to ensure proper solder connection interface

between the board and the package. With the correct pad geometry, the packages will self align when subjected to a solder reflow process.

The power dissipation for a surface mount device is a function of the drain pad size. These can vary from the minimum pad size for soldering to a pad size given for maximum power dissipation. Power dissipation for a surface

mount device is determined by TJ(max), the maximum rated junction temperature of the die, RθJA, the thermal resistance

from the device junction to ambient, and the operating temperature, TA. Using the values provided on the data sheet, PD can be calculated as follows:

The values for the equation are found in the maximum ratings table on the data sheet. Substituting these values into the equation for an ambient temperature TA of 25°C, one can calculate the power dissipation of the device. For a D3PAK device, PD is calculated as follows.

PD = 150°C ± 25°C = 2.31 Watts

54°C/W

The 54°C/W for the D3PAK package assumes the use of the recommended footprint on a glass epoxy printed circuit board to achieve a power dissipation of 2.31 Watts. There are other alternatives to achieving higher power dissipation from the surface mount packages. One is to increase the area of the drain pad. By increasing the area of the drain pad, the power

dissipation can be increased. Although one can almost double the power dissipation with this method, one will be giving up area on the printed circuit board which can defeat the purpose of using surface mount technology. For example, a graph of RθJA versus drain pad area is shown in Figure 11.

Figure 10. Thermal Resistance versus Drain Pad Area for the D3PAK Package (Typical)

Another alternative would be to use a ceramic substrate or an aluminum core board such as Thermal Clad . Using a board material such as Thermal Clad, an aluminum core board, the power dissipation can be doubled using the same footprint.

Prior to placing surface mount components onto a printed circuit board, solder paste must be applied to the pads. Solder stencils are used to screen the optimum amount. These stencils are typically 0.008 inches thick and may be made of brass or stainless steel. For packages such as the SC±59, SC±70/SOT±323, SOD±123, SOT±23, SOT±143, SOT±223, SO±8, SO±14, SO±16, and SMB/SMC diode packages, the stencil opening should be the same as the pad size or a 1:1 registration. This is not the case with the DPAK and D2PAK packages. If one uses a 1:1 opening to screen solder onto the drain pad, misalignment and/or ªtombstoningº may occur due to an excess of solder. For these two packages, the opening in the stencil for the paste should be approximately 50% of the tab area. The opening for the leads is still a 1:1 registration. Figure 12 shows a typical stencil for the DPAK and D2PAK packages. The pattern of the opening in the stencil for the drain pad is not critical as long as it allows approximately 50% of the pad to be covered with paste.

SOLDER PASTE

OPENINGS

STENCIL

Figure 11. Typical Stencil for DPAK and D2PAK Packages

The melting temperature of solder is higher than the rated temperature of the device. When the entire device is heated to a high temperature, failure to complete soldering within a short time could result in device failure. Therefore, the following items should always be observed in order to minimize the thermal stress to which the devices are subjected.

•Always preheat the device.

•The delta temperature between the preheat and soldering should be 100°C or less.*

•When preheating and soldering, the temperature of the leads and the case must not exceed the maximum temperature ratings as shown on the data sheet. When

using infrared heating with the reflow soldering method, the difference shall be a maximum of 10°C.

•The soldering temperature and time shall not exceed 260°C for more than 10 seconds.

•When shifting from preheating to soldering, the maximum temperature gradient shall be 5°C or less.

•After soldering has been completed, the device should be allowed to cool naturally for at least three minutes. Gradual cooling should be used as the use of forced cooling will increase the temperature gradient and result in latent failure due to mechanical stress.

•Mechanical stress or shock should not be applied during cooling.

*Soldering a device without preheating can cause excessive thermal shock and stress which can result in damage to the device.

*Due to shadowing and the inability to set the wave height to incorporate other surface mount components, the D2PAK is not recommended for wave soldering.