Jumping Through Hoops

A normal gate array prototype cycle takes about 8 weeks.  There is a week to make masks, 3 weeks for wafer processing, another 2 weeks for assembly, a week for test and bake, and a final week that taken by shipping between the various stages.

Sometimes, 8 weeks is too long, particularly if a customer faces a lines-down situation.  In these cases, expedites can help to reduce the total cycle to under 3 weeks.

The first part of an expedite is to pay the wafer fab to turn the lot into a hot lot (or bullet lot).  This will reduce the fab and mask time from 4 weeks to about 10 days.

Expediting the assembly is more complicated.  Most overseas manufacturers are pretty efficient, and an expedite will reduce their cycle time from two weeks to about 1 week.  This is dependent on their capacity at any given time.

 Domestic assemblers are an option, but they must have the tooling for the specific package you need.  With expedites, that can usually turn a package in 2 to 3 days.  And there is an additional time savings to be had from the reduced shipping times.

Another option is to use a “glob-top” approach.  This involves taking an existing package, cutting a hold in it, and removing the original die.  The new die is put into the cavity and bonded.  Then it is covered with plastic, resulting in a package that is physically identical to the original.  There are potential reliability issues, so glob-tops are only for engineering prototypes.  Either approach will deliver assembled parts in about 3 days.

Another 2 days can be saved by eliminating bake if the customer plans to either use a socket, or to hand solder the part on the board.

When all of this is taken together, expedites can reduce the cycle time down to a little over 2.5 weeks.

I should note that an expedite charge covers a best effort, and is not a guarantee of ultimate performance.  Still, it had a very high probability of delivering parts in a third of the normal cycle time.