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26 March 2014

Hot Gas Rework

Posted in Application Notes

Equipment: Model 4450 Hot Gas Rework Station

 

Application: Hot Gas Rework
Equipment: Model 4450 Hot Gas Rework Station

 

 

Process: Epoxy bonded die attached to circuits including other die and discrete components sometimes fail and need to be replaced.  Hybrid circuits on ceramic substrates are common examples of circuits that may need die reworked and they are the example in this paper, but the same techniques will apply to other applications.

Die are removed by applying enough heat to the bond to break down the adhesive without causing harm to the substrate or nearby devices.  Removal heat (approx. 350°C) must be confined to the die being reworked, but the entire substrate must be heated (approx. 150°C) to avoid thermal shock.  A light force is applied to shear the bond site and remaining wire bonds are also scraped off.  The site is now ready for epoxy and a new die.

 

Machine Discussion: The principle feature of a system that performs die rework is spot heating.  The heating device needs to confine heat within an area range of 10-mil sq. up to 15" sq.  The die undergoing rework needs to be heated to temperatures ranging up to 350°C without affecting nearby components.

Precision heating of die can be achieved in several ways.  A direct contact tool can be used to apply heat to the die.  Another method involves the use of a focused light beam.  Heated gas, the method used in this discussion, is another viable rework tool.  All of these methods used in this discussion, is another viable rework tool.  All of these methods confine heating to the rework site and accommodate a variety of die sizes.

Spot heating can cause the substrate to crack due to uneven heating.  To prevent cracking, the substrate should be heated to a minimum temperature of 150°C.  A rework system needs a holder that can evenly heat substrates up to 350°C.  The holder should be fixed to the machine and have a means of clamping down the substrate for stability during die removal.

Heating the die breaks down the epoxy bond so that the die can be removed with a minimum amount of force.  A device is needed that will shear the die away from the substrate without impacting other components.

The rework site needs to be properly cleaned up before die can be re-attached.  Hand-held tools are necessary for scraping excess epoxy and wire bonds off the substrate.

Use of a microscope with an appropriate lighting system is helpful in viewing the alignment of the heating system to the die and other precise processes, such as die removal and substrate cleanup. 

 

Machine Features: The Model 4450 is s hot gas rework station that uses low gas volume and high heating temperatures during the die rework process.  This system delivers 5-10 cubic ft.  of gas per hour, which is heated up to 650°C..  The low volume and high heat afford a short bond breakdown time of 20-30 seconds.  This prevents the entire substrate from heating through and damaging its components.  A temperature controller maintains closed loop control of the hot gas temperature.

An interchangeable quartz nozzle delivers a stream of heated gas over the die.  Various size nozzles are available to work with a range of die sizes.

This machine comes with a standard 2" sq. stage that can be heated to 350°C..  The stage has an aluminum workchuck with an adjustable vacuum back-up plate and vacuum hold-down to keep the substrate stable during die shearing.  The stage moves under the nozzle for alignment and automatically locks down prior to hot gas application.

A side die ejector is available to apply pressure to the die while it is heated.  When the epoxy breaks down, the ejector moves the die slightly off the bond site for removal.

A zoom microscope that mounts to the system is available to aid in the rework process.

 

Required Equipment: The following equipment from Semiconductor Equipment Corporation is required to perform this application:
 
  • Model 4450 Hot Gas Rework Station
  The following equipment from Semiconductor Equipment Corporation is optional to perform this application:
 
  • B & L Stereo Zoom Microscope
  • Illuminator
  • Side Die Ejector

 

Contact: Lester Salvatierra
Sales Manager
Phone: (805) 529-2293 x 21
Fax: (805) 529-2193
E-mail: Click Here