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AN555 Dataheets PDF



Part Number AN555
Manufacturers Motorola
Logo Motorola
Description Mounting Stripline Opposed Emitter Transistor
Datasheet AN555 DatasheetAN555 Datasheet (PDF)

MOTOROLA Order this document by AN555/D SEMICONDUCTOR APPLICATION NOTE AN555 MOUNTING STRIPLINE-OPPOSED-EMITTER (SOE) TRANSISTORS Prepared by: Lou Danley INTRODUCTION The Stripline Opposed Emitter (SOE) package presently used by Motorola for a number of rf power transistors represents a major advancement in high frequency and www.DataSheet4U.com thermal performance. This Application Note discusses the SOE package, its advantages and limitations as well as a number of considerations to avoid.

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MOTOROLA Order this document by AN555/D SEMICONDUCTOR APPLICATION NOTE AN555 MOUNTING STRIPLINE-OPPOSED-EMITTER (SOE) TRANSISTORS Prepared by: Lou Danley INTRODUCTION The Stripline Opposed Emitter (SOE) package presently used by Motorola for a number of rf power transistors represents a major advancement in high frequency and www.DataSheet4U.com thermal performance. This Application Note discusses the SOE package, its advantages and limitations as well as a number of considerations to avoid improper usage. An understanding of a few basic principles in regard to mounting and heat-sinking of this package can help avoid cases of poor performance or device damage. Two general package types — the stud-mounted and flange-mounted SOE packages will be discussed. Each of the general types is available in a variety of sizes. Typical package outlines of the two SOE packages are shown in Figure 1. similar in construction. The body of the package is a Berylium Oxide (BeO) disc. Berylium Oxide was chosen due to its high thermal conductivity. Attached to the bottom of the disc is a copper stud which is for heat transfer and mechanical mounting. The lead frame is attached to a metalized pattern on to the top surface of the BeO disc. The actual shape of the leads differs between the various package types. Finally an Alumina ceramic cap is attached to the top of the disc over the leads providing a protective cover for the transistor die. An understanding of the basic structure of the SOE package is essential to proper usage of these devices in respect to heat-sinking and mechanical mounting. Since these two areas present the greatest problem to users, they will be discussed in detail. ADVANTAGES OF THE SOE PACKAGE The primary electrical advantages of the SOE packages are the low inductance strip line leads which interface very well with the microstrip lines often used in UHF-VHF equipment and the good collector to base isolation provided by the two emitter leads. The two emitter concept promotes symmetry in board layout when combining devices to obtain higher output power. Both emitter leads should always be used for best performance. HEAT-SINKING THE SOE PACKAGE In order to properly understand the thermal considerations involved in mounting SOE type packages, it is necessary to lay some groundwork in the area of heat flow. Table 1 gives equivalent Thermal and Electrical parameters which may be used to relate Thermal properties to more familiar electrical units. Semiconductor power devices are usually guaranteed to have a certain thermal performance as stated by the thermal resistance of the device from the junction to the case, or mounting surface — θJC. How to get the heat out of the case has generally been left to the user. In any dynamic heat flow problem, the heat must go somewhere, otherwise there will be a continuous rise in the temperature of the system. In text books, there always seems to be an “infinite heat sink” DESCRIPTION OF THE SOE PACKAGE Figure 2 displays the component parts on a stud-mounted SOE package. This package will be used as an example since both the stud and flange-mounted packages are very Figure 1. SOE Packages RF Application © Motorola, Inc. 1993 Reports 1 AN555 Ceramic Cap Transistor Chip Leads Metallic Pattern www.DataSheet4U.com Surface S BeO Disc Wrench Flat Arizona summer. In such an environment, temperatures might reach as high as 80°C (176°F). The heat-sink system for such a radio should therefore be tested at a minimum ambient temperature of 80°C. The method that should be applied in this test would utilize a fine wire thermocouple rigidly secured to the stud of the rf power transistor for which the test is being conducted. The system, which in this case would include all parts of the radio which would contribute heat, should then be operated under maximum heat generating conditions, in the high temperature environment specified. Careful measurement of the temperature of the device under test would then give the difference in temperature between the case of the transistor and the controlled ambient. If the case and ambient temperatures are known, as well as the power levels in the transistor, the thermal resistance from the transistor case to the ambient can be calculated. The first step is to obtain the power being dissipated by the device. Pd = P1 + P2 – P3 (1) where: Pd = power being dissipated by the transistor in watts; P1 = dc power into the transistor in watts; P2 = rf power into the transistor in watts; P3 = rf power out of the transistor in watts. This value of Pd is used to obtain the θCA value from the equation: θCA = TC – TA Pd (2) Figure 2. Component Parts of SOE Package Table 1. Thermal Parameters and Their Electrical Analogs Thermal Parameter Temperature difference Heat flow Thermal resistance Heat capacity Thermal conductivity Quantity of heat Time Thermal time constant Electrical Analog Units* °C watts °C/watt watt-sec/°C cal/seccm-°C cal sec sec Symb.


AN555 AN555 ER060-100


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