Discrete transistors are individually packaged transistors. Transistors come in many different semiconductor packages (see image). The two main categories are through-hole (or leaded), and surface-mount, also known as surface-mount device (SMD). The ball grid array (BGA) is the latest surface-mount package (currently only for large integrated circuits). It has <answer>solder "balls" on the underside in place of leads</answer>. Because they are smaller and have shorter interconnections, SMDs have better high-frequency characteristics but lower power rating.
What is a ball grid array composed of?
solder "balls" on the underside in place of leads