THE PROBLEM: MORE PINS

From tens of pins to thousands

I/O count grew faster than packages could

Early chips needed only a handful of connections, and packages evolved again and again to keep up as that number grew into the hundreds, then thousands. Each new package style exists because the previous one ran out of room.

Package history is really just I/O count, pushing back against physics.

THROUGH-HOLE TO LEADED

Pins around the edge

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DIP

Dual in-line package: two rows of pins, plugged through a board

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QFP

Quad flat package: fine leads on all four sides, surface-mounted

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The limit

Perimeter leads only scale with the package's edge length

Both styles put every connection around the outside edge.

AREA ARRAY

Connections spread across the whole underside

A ball grid array, BGA, abandons the edge-only approach entirely. Solder balls cover the package's whole underside in a grid, so connection count scales with area instead of perimeter, letting one small package carry thousands of connections.

Area array is the same idea as flip-chip, one level up: use area, not just edge.

WHY AREA ARRAY WINS

Area grows faster than edge length

double the side length, quadruple the area

A package's perimeter only doubles when its side length doubles, but its area quadruples. An area-array package like a BGA can therefore carry far more connections than a leaded package of the same size, which is why BGAs and their smaller cousins dominate modern high-pin-count chips.

The same math that favors flip-chip over wire bonding favors BGA over QFP.

UNIT 39 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered how packages evolved from a handful of pins to thousands, and why.