Chip magicians at work: patching at 45nm

Needless to say, whenever a bug is encountered it needs to be taken care of. Whether the problem is with the logic or an unfortunate implementation of a circuit that limits the clock speed: in order to get from the A0 version to a product, a fair bit of tweaking is necessary.

However, some bugs are very difficult to trace. Especially when the design seems OK or the simulations predict that a slow circuit should have been fast, the designers can apparently do little more than change a few things and hope that it improves the results... but Intel has a couple of very expensive machines designed to tackle just this sort of situation.

A processor suffering from an 'inexplicable' problem will receive a special treatment. First, the standard metal heat spreader is removed. Next, the protective layer that lies underneath is stripped from the chip, leaving only 10µm from the original 750µm. The chip is subsequently placed within a specially designed test socket with a pure-diamond heatsink. Diamond is a pretty good thermal conductor, but, more importantly, it is also transparent.

As it happens, one of silicon's lesser known properties is that it is also transparent: not to the naked eye, but infrared can penetrate it. Hence a very precise laser can be used to see what goes on inside the chip. For this purpose, Intel has a custom built machine costing 2,6 million dollars at its disposal, allowing it to scrutinize the individual transistors to check whether they are live or not, and this with picosecond accuracy - a millionth of a millionth of a second. It lets Intel see quite literally where and how fast the transistors switch.

One of the interesting features of the test platforms that are used, is the possibility to slow down the chip clock. The operator of the machine can choose to go from billions of ticks per second to a single tick, allowing human eyes to follow what is going on. With the same ease the clock can be stopped altogether. If needed, that gives the engineers the luxury to be able to stare for two hours at a situation that would normally be over in a fraction of a nanosecond.

In order to find transistors, the chip design is automatically projected over the images.

A second machine makes things even more fancy: it can zoom in to details of less than a nanometer and even execute instructions at that level. This is done by evaporating certain chemicals into the laser beam, which are then shot directly into the chip. Using corrosives, connections can be broken, while metal and silicon are used to make new structures.

This machine is so sensitive that it had to be stabilized after traffic ramps had been constructed outside. Vibrations caused by cars passing over them made the images bounce up and down.

The technology saves Intel huge amounts of time. Having the factory create a new revision takes at least four to six weeks, but with this machine it can be done within a day. Although what comes out isn't meant for mass production, it has happened: two weeks before the original Pentium 4 was supposed to launch, a bug was found in the southbridge of the chipset. Intel engineers scrambled to patch hundreds of chips with this kind of machines, in order to still be able to ship motherboards in the first few weeks.