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01 February 2017

SEC Model "450 Hot Shot" Rework Station

Posted in Blog

We still make the Model 450 Hot Shot Gas Rework Station. The Model 450 is uniquely qualified for rework of hybrid devices. It was originally developed to solve a problem with the manufacture of LED watches. There was a yield problem with several die in the early versions so a method was needed to remove and replace the die. The Model 4400 was developed.

The Model 4400 used a tubular quartz nozzle with a serpentine wire heater element. The nozzle typically had a 0.060" opening. There was a heated stage with vacuum to hold the substrate. A die pusher and microscope were optional. The unique capability was that the nozzle could heat a die hot enough to break down the epoxy without overheating the nearby die. The die pusher would apply force to the side of the die until it popped free. The die pusher doubled as a scraper to clean the bond site for attachment of a new die.

Sometime in the 80's the Model 4400 was redesigned for better control of the stage and gas temperatures. The nozzles were also redesigned to be interchangeable. Various shapes and sizes of nozzles became available as die sizes grew and SMT became popular. The redesigned 4400 became the 4450 and eventually the Model 450.

There are still applications which the 450 is uniquely qualified for such as implanted medical devices and high rel hybrid circuits. Complicated hybrid circuits are more likely to need rework as the complexity increases and the volume of production decreases. In many cases the die are attached to a ceramic substrate with epoxy and wire bonded. The rework process cannot be done by most SMT rework systems on the market.

The main issue is that the die are small and very close to other components. The substrate also must not be overheated or heated unevenly which will cause stress. Most SMT systems on the market blow a lot of hot air which over heats other components. Their work holders are designed for circuit boards and they don't have a convenient way to push the die off without causing other damage.

The Model 450 solves all of these problems. The hot gas (Nitrogen) is heated to a fairly high temperature, normally about 500 C. The volume of gas is controlled to a low flow rate of about 5-10 SCFH. The nozzle is selected to be slightly larger than the die for optimal performance, however this is not critical. The stage temperature is set to be well below the maximum temperature for the assembled substrate, but high enough to avoid stress in the substrate caused by spot heating. Typical stage temperature is about 125 C.

To remove a die the operator places the substrate on the stage against the backstop and turns on the vacuum. The die is centered under the nozzle. The operator has manual Z motion position control of the nozzle. The side die pusher is aligned almost touching the die. The gas flow and vacuum to hold the stage are started by the button on the stage or the foot pedal. The die side pusher is adjusted to apply some pressure against the die. When the heat has broken down the epoxy the die will break free. The whole cycle takes about a minute. The 450 can also be used to remove and replaced soldered SMT components.