ST AN1294 APPLICATION NOTE

AN1294

Application note

PowerSO-10RF: the first true RF power SMD package

Introduction

During the last years, as the size of electronic components has decreased and their reliability increased, there has been a need across the board for various surface-mounted components. The PowerSO-10RF is not just a new package, it is a new concept in a small outline plastic package for RF power applications. Such applications have a great need for surface-mount device (SMD) packages but, up until now, the available bipolar technology did not allow for such types of package.

The main advantages of this new RF plastic package are excellent thermal performance, high power capability, high power density and suitability for all reflow soldering methods.

The purpose of this application note is to demonstrate that the PowerSO-10RF is the perfect solution for the new RF power LDMOS products recently introduced by STMicroelectronics.

November 2009

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www.st.com

Contents	AN1294

Contents

1	RF Power package requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		5
2	What is the PowerSO-10RF? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		6
	2.1	Brief overview of the PowerSO-10RF technology . . . . . . . . . . . . . . . . . . .	6
	2.2	Delivery information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	7
3	Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		8

3.1 Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2 Segments and applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4	LDMOS in PowerSO-10RF/typical RF performances . . . . . . . . . . . . . .		. 9
5	Quality and reliability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		11
6	Soldering method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		12
	6.1	Vapor phase reflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	12
	6.2	Infrared heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	12
	6.3	Soldering paste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	12

6.3.1 Applying the soldering paste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

6.4 Placement of parts and drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.5 Avoiding stresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

7	Mounting recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	15
8	Thermal resistance and maximum power dissipation capability . . . . 17
9	Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	18
10	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	19

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AN1294	List of tables

List of tables

Table 1. Features and benefits of the PowerSO-10RF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Table 2. Description of reliability tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Table 3. Thermal resistance and maximum power dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Table 4. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

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List of figures	AN1294

List of figures

Figure 1. LDMOS structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Figure 2. PowerSO-10RF package construction (JEDEC MO-184 standard) . . . . . . . . . . . . . . . . . . . 6 Figure 3. PowerSO-10RF straight and formed lead versions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Figure 4. PD57045S-E in PowerSO-10RF versus SD57045-01 in ceramic package . . . . . . . . . . . . . 9 Figure 5. Power gain versus output power/ceramic vs. plastic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Figure 6. Power gain versus output power/straight leads vs. formed leads. . . . . . . . . . . . . . . . . . . . 10 Figure 7. Recommended heat profile/reflow soldering for PSO10RF lead-free. . . . . . . . . . . . . . . . . 14 Figure 8. PowerSO-10RF recommended pad layout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Figure 9. PowerSO-10RF recommended pad layout with via holes . . . . . . . . . . . . . . . . . . . . . . . . . 16 Figure 10. Mounting on copper base plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

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AN1294	RF Power package requirements

1 RF Power package requirements

The most important requirement in an RF power package is a good heat dissipation capability. The package must be able to dissipate heat so that the die temperature remains below a pre-defined maximum temperature, above which damage might occur. Other important features of a good RF package include low inter-electrode capacitance, low parasitic inductance, high electrical conductivity, reliability and low cost.

Figure 1. LDMOS structure

In conventional DMOS or bipolar vertical technology, an electrical insulator (Beryllium oxide or BeO, which is highly toxic), is required to isolate the drain from the ground. In an LDMOS structure where both the N+ source and the drain region are on the die surface with a laterally diffused low resistance P+ sinker connecting the source region to the P+ substrate and source terminal (Figure 1: LDMOS structure on page 5), this insulator is no longer needed. This not only means that electrical and thermal performances are greatly improved, but also that the standard DMOS ceramic package (with BeO) used for 1 W and above devices can be replaced by a plastic package.

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What is the PowerSO-10RF?	AN1294

2 What is the PowerSO-10RF?

The PowerSO-10RF is an RF optimized version of PowerSO-10™. It is the first STMicroelectronics JEDEC approved high-power SMD package and has already been in production for almost 10 years, mainly for products such as rectifiers, protection diodes, triacs and power transistors (bipolar, MOSFETs and IGBTs), which have already proven their reliability in automotive, telecom and computer applications where reliability standards are very high.

2.1Brief overview of the PowerSO-10RF technology

Figure 2. PowerSO-10RF package construction (JEDEC MO-184 standard)

The plastic package of a power chip has four main functions.

●Electrical interconnection between the silicon LDMOS chip and the external circuit.

●Protection from chemically aggressive agents, for long-term reliability.

●Mechanical support to the LDMOS die to make handling easier.

●A thermally conductive path to transfer the heat generated in operation from the silicon LDMOS die to the ambient or to the heatsink.

The PowerSO-10RF is the result of an optimization between conflicting requirements of good thermal properties and small dimensions. Its low thermal resistance is the result of a large copper heat spreader (slug) integrated into the package body, in direct contact with the silicon LDMOS die.

The metal frame of the device, consisting of the copper slug (Cu/KFC) and the package leads is known as the leadframe (Cu/CUPROFOR). The leadframes for a number of individual devices are manufactured in a single continuous strip to simplify handling and processing.

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