AN1294 Datasheet, PDF (7/20 Pages) STMicroelectronics – During the last years

AN1294
What is the PowerSO-10RF?
After the silicon LDMOS wafer is cut into individual dice; each die is brazed onto the copper
slug using a high melting temperature (> 280° C) tin solder alloy such as Pb97.5Sn1Ag1.5.
The process used to attach the die to the slug is critical in maintaining the thermal
performance of the RF power device. It must produce a uniform, void-free joint between the
silicon LDMOS’ back metallization and the copper slug in order to avoid hot spots in the
active area and, in the long run, thermal fatigue.
After the die is attached, the silicon LDMOS die is connected to the leadframe with Au or Al
wires that are ultrasonically bonded to both the metallization on the chip (Al alloy: AlSiCu)
and to a nickel layer on the leadframe. The diameter of the wire used is chosen according to
the current to be handled using the approximated rule of about 1 mil (25 µm) per Amp.
Molding is the third step of assembly. The leadframe strips are positioned in molding
cavities, which are then pressure-filled with liquid thermosetting epoxy, which after
solidification provides a hard, reliable and cost-effective encapsulation (the molding
compound is Sumitomo Eme 6300HV with a molding temperature of 200 °C +/- 20 °C).
The last major process is to coat the leads with a low melting temperature thin solder alloy
(tin plating: 7 µm min/15 µm max) to provide a "wettable" surface when the device is
soldered to the printed circuit board (PCB).
After singulation (separation of the leadframe strips into individual devices) and lead forming
(bending of the leads into the required shape), the devices are marked and tested before
being packed and shipped.
There are two available lead versions, shown in Figure 3.
● Formed leads for SMD applications and power dissipation (Pdiss.) < 15 W.
● Straight leads for standard RF mounting on heatsink and Pdiss. > 15 W.
Figure 3. PowerSO-10RF straight and formed lead versions
2.2
Delivery information
The PowerSO-10RF is delivered in a tube of 50 pieces. A bulk quantity equals 250 pieces
(available for both lead versions). A tape and reel form of 600 pieces is also available.
Doc ID 7604 Rev 3
7/20