How to decap an IC

[Grant Stockly]

<Part of the previous post>
Diane,

Yes, hot fuming sulfuric and/or hot fuming nitric are used as standard procedures for removing plastic from IC's. The process is not quite that simple. For example, water rinses will almost certainly etch the bond pads on the IC and thus removing connection to the outside world. Additionally, the plastic contains fire retardants which some regions don't like being washed down the drain. There is more detailed help through EDFAS.org (one of ASM's branches). B&G International sells a very safe, effective etcher which performs decapsulation automatically in minutes.

I have no association with B&G International.

David Saxon
Analytical Microscope Services
11826 Reservoir Rd. E.
Puyallup, WA 98374
253-848-7701 voice & fax
email: info-at-analyticalmicroscope.com
website: www.analyticalmicroscope.com

[Grant Stockly]

<Part of the previous post>

Diane,

I used to do failure analysis on semi conductor memories which were starting to be made of plastic/epoxy with glass rods about 20 years ago.

I have some technics and possible help but its too much to write. Basically you drill a small hole about 0.1" deep then heat the IC on a hot plate and then you drop your acid to remove the plastic. I dont know chemistry, I'm and Electronics Technician. I did this work with a meterial sicentist, my mentor.

We used fumming sulfuric acid and fuimg nitric acid, also some type of organic pink and blue solutions to stop some of the acids etching effect.

The company back then was Burroughs Corp. today is Unysis.

I presently work for the U S Department of Energy in New York City. My phone number is 212 6203650, I'll be happy to walk through some ideas and things I learned.

Regards
Peter Roiz

[Grant Stockly]

<Last part of the previous post>

Perhaps it's time to comment on this thread.

Dichloromethane and dimethylformamide are relatively effective disrupters of most epoxies but their action is accompanied by great swelling because the polymer becomes engorged with the liquid before any significant solvation takes place. This will destroy wire bonds on an IC.

Fuming (essentially anhydrous) sulfuric acid acts by the completely different process of sulfonating reactive groups that remain on the polymer. The depolymerized and sulfonated byproducts are quite soluble not only in the acid but usually in water as well. The worst thing that you could do in this relatively straightforward process is to wash with water at intervals because this would initiate almost instantaneous corrosion. It would be advisable for a chemist, as someone trained in the handlingof reactive materials, to carry this out or at least to establish procedures and train others with less experience. The action of sulfuric acid in this regard is quite different than that of nitric. Nearly anhydrous nitric acid (completely anhydrous is extremely difficult to prepare) is a very powerful oxidizer and could lead to unstable, dangerous byproducts whereas the sulfonates resulting from the sulfuric acid reaction are relatively stable. Water must, of course, be prevented from splashing into any concentrated acid, especially sulfuric.

A very strong acid such as sulfuric behaves completely differently in the absence of water. Since most acids are highly hygroscopic and are sold as water solutions, most people do not observe this other side of their behavior. Without water to create an ionized electrolyte, corrosion of metals will not take place. I have de-encapsulated ICs for failure analysis in 200 degree sulfuric acid and been able to operate the IC without replacing the .001" aluminum wirebonds that it came with. I recall one instance where our company built prototype hybrid microelectronic circuits out of such de-encapsulated ICs when their supplier was late getting a new design on the market and the only ones available were already encapsulated.

The key is to realize that water must be excluded until the sulfonating acid has been completely rinsed away by a non-aqueous liquid. As Mr. Saxon said, there are simple and safe devices available for doing this operation. However, with proper care and protective gear it can be done in a beaker on a hot plate in a fume hood. A few ml.s of sulfuric acid are heated to drive off water until heavy vapors are observed over the liquid (which may darken during heating due to trace impurities). The IC is carefully lowered into the hot acid and a vigorous reaction ensues with the epoxy almost instantly washing into the solution. After a few seconds the IC is then quickly lifted out and held over a receiving vessel and flooded with a stream of ethanol. Only after this is a final rinse in deionized water carried out, followed by fresh electronic grade ethanol and forced drying in warm air.

The ready made devices which carry out the operation are typically a small bowl with a hinged lid from which air is withdrawn by a gentle vacuum. An inert metal feeder tube leads from a heated reservoir for the sulfuric acid and passes through the wall of the bowl to a position where the encapsulated device is secured. When the lid is closed and the slight vacuum applied, the hot acid is pulled into the bowl over the device. It is somewhat self-limiting in that, if the lid is opened, there is no driving force to bring more acid into the container. Naturally, the vacuum source needs to be protected by a trap and all waste products properly handled no matter how the procedure is carried out.

John Twilley
Conservation Scientist
(formerly, Manager of the Reliability Analysis Center, Teledyne Microelectronics)

From daemon Fri Jan 25 08:35:53 2002

[Grant Stockly]

From: Darrell Miles : milesd-at-US.ibm.com
Date: Fri, 25 Jan 2002 11:45:46 -0500
Subject: IC package removal

Contents Retrieved from Microscopy Listserver Archives
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Body of Message

Jon,

If it is the black "plastic" (glass filled epoxy), nitric acid works on some, and sulfuric acid works on most. There are also some chemicals called "Dynasolve", that we use various types of. The differences are in the speed with which the material is removed, and what damage is done to interconnects, etc. If you watch the time you have the sample in sulfuric acid, it works for most parts.

Hope this helped.
Regards,
Darrell

[Grant Stockly]

I have sent one PAL (Apple calls them HALs on the Mac boards) to MEFAS. You can find them at http://www.mefas.com

They offer a decapsulation service at only $45 per part with a 2-3 day turnaround. I have sent them the ASG PAL since its the only one I don't have equations for. I have requested the service of decapsulation with cleaning options for photography. This means they don't pay attention to the bond wires and attempt to clean the surface.

Their website describes their decapsulation service as follows.

Decapsulation is a technique for exposing the internal components of a package device. There was a time when a hot plate and concentrated nitric acid were capable of decapping integrated devices (IC’s). However, advancements in device packaging introduced new plastic encapsulants and the array of solder bumped external leads package designs. Our jet etching systems are capable of exposing any package die without melting solder bumps, etching bond pads, or destroying external leads. The system sprays high temperature nitric and/or sulfuric acid through a fine diameter nozzle head. By computer control of the temperature, pressure, and time of the etching process a uniform etch cavity is created which exposes the IC.

Of course not all devices need the selectivity of our automatic decapsulator. For these devices we x-ray the device to measure the internal die, cut the proper die cavity in the package, and finally eye drop concentrated nitric acid in the cavity to remove the plastic from the IC.

Once decapped, analyses such as inspection, microprobe, FIB rework, delayering, or even retesting can be accomplished. The device will remain functional.

I liked how they described the entry level procedure... "eye drop concentrated nitric acid in the cavity to remove the plastic from the IC."

Most companies I've found don't go into detail about how they do their service, and wouldn't admit it could be done with a hotplate and eye dropper.