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Old 09-05-2005, 02:19 PM
Grant Stockly Grant Stockly is offline
Join Date: Jan 2005
Posts: 447

<Part of the previous post>

Diane: attached is a text document outlining the procedure my FA lab uses. Yellow fuming nitric is usually the acid of choice. If you can get a few extra parts to practice on, that would be best. And you're right, plasma takes FOREVER. If I can be of any more help, please let me know.

Becky Holdford (
972-598-1291 (pager)
KFAB Physical Analysis Labs--SEM/FIB/FA
Kilby Center West
Texas Instruments, Inc.
Dallas, TX


  1. Milling machine and appropriate end mills
  2. Stabilo SuperFine OH pen or equivalent
  3. Fume hood properly equipped for exhausting acid fumes and solvent vapors (see reference 3.4)
  4. Explosion proof hot plate (see reference 3.4)
  5. Ultrasonic cleaning apparatus
  6. An optical microscope capable of 100X to 500X magnification, equipped with a lighting system.
  7. Chemical resistant latex gloves
  8. Chemical resistant laboratory coat
  9. Chemical resistant safety glasses (see reference 3.5)
  10. Hand tools (tweezers, scalpels and etc.)
  11. Plastic micro-pipette
  12. Fuming red nitric acid
  13. Yellow nitric acid
  14. Methyl alcohol
  15. Acetone


Record all of the device markings that are on the top and bottom sides of the devices prior to starting any of the decap operations.

Determine the exact location of the chip within the package and mark the top of the device package showing the chip perimeter, using a Stabilo SuperFine OH pen and a straight edge. A SAM plot or X-ray image may be used to help determine the exact location of the chip and also to determine the thickness of the mold compound covering the chip.

Note: This should be done on devices having large chips. Devices with small chips (less than 0.125 inches in their longest dimension) do not require this step.

Mill a cavity out of the plastic package that is centered over the chip. The size of the milled cavity should typically be .050 to .100 inches larger than the length and width dimensions of the chip. The depth of the milled cavity depends on the thickness of the mold compound and the location and loop height of the bond wires. During the milling operation use a vacuum line to pick up the loose plastic particles generated.

Caution: do not mill into the bond wires or the chip. Mill counter bores on devices with chip dimensions greater than 0.400 inches on a side. These counter bores should be made on one or more levels within the bond pad perimeter and at the outermost corners of the cavity (this is necessary to facilitate etching of the mold compound at the corners of the chip before the sides are exposed and subsequent damage to the leadframe). Care must be taken during the milling operation to avoid excessive pressure on the mill resulting in filler induced damage to the chip P.O. The end mill should not bind, bend, or "smoke" during the milling operation.

All etching must be performed in a chemical hood that meets the requirements defined in references #.3 and 4. Heating of acid or device prior to application of acid must be done using an explosion proof hot plate that meets the requirements of reference #4. Obtain the appropriate acid for use on the mold compound being removed. Following are the acids that have been identified for the removal of the various mold compounds. Mold Compound Acid/Temperature Shinetsu Red fuming nitric acid at 140-150 degrees Celsius Plascon & Sumitomo Red fuming or yellow nitric acid 140-150 degrees Celsius

Note: Fuming sulfuric acid reacts with exposed aluminum bond pad metallization and may result in ball bond discontinuity thus hampering further analysis.

  • When using red fuming nitric acid it may be helpful to start the etching process using a mixture of red and yellow nitric acids in order to slow down the etch process until a "residue crust" is formed over the cavity and then switch to the red nitric acid.
  • Apply the acid in drops using a plastic micro-pipette. The drops should be placed in the center and at the corners of the cavity in approximately a 1:1 ratio.
  • Allow the acid to react with the mold compound and form a crust of dissolved compound. Caution: Do not allow the crust to dry out completely before adding additional drops of acid.
  • Remove the dissolved material using cotton swabs or by rinsing with acetone when the dissolved materials threaten to spill over the cavity. Caution: Rinse the device immediately with acetone if acid spills onto the package pins.
  • Soak the device in acetone for a minimum of 10 minutes, followed by a spray of methanol to remove loose residue and to clean the residue from the cavity rim.
  • Perform a thorough microscopic inspection to determine whether all necessary areas of the chip are exposed.
  • If dried mold compound residue persists on the chip surface, use the following in the order shown to attempt removal:
  • Solvent bath (such as methyl alcohol) in ultrasonic cleaner
  • Several drops of room temperature fuming sulfuric acid applied to the chip (with the chip at room temperature) for several seconds then rinse the device in DI water.
  • Several drops of fuming sulfuric acid applied to the chip with the chip on a 100 degree Celsius hot plate. Note: Fuming sulfuric acid will attack aluminum bond pads and is therefore the method of last resort.
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