Mounting and cleaning dies


You can lose a small die at the slightest false movement, and it’s a pain to clean.

Dealing with unmounted dies is hard.

Beeswax

Beeswax have multiple advantages:

  • it doesn’t get dissolved by immersion oil or acetone
  • but it can be cleaned off with naphta (dearomatized white spirit in France)
  • wax solidifies in seconds so you can use your sample immediately
  • if leveling is not good, just heat again
  • usually, there is no need to press the surface of the die, so no contamination
  • this is a good solution for samples to be observed with water dipping objectives

But also a few drawbacks:

  • It’s not easy to use with very small dies
  • If you are not careful wax can overflow on the die.
    Especially if there is too much wax.
  • It’s a little hard to clean with dearomatized white spirit (residues)

Preparation

I prepare a few glass slides on which a tiny sliver of beeswax is placed.

Then I use hot air (heatgun) to heat a small heatsink and place it on a cardboard sheet (very bad heat conductor).

A slide is placed on the hot heatsink, wax get liquid and I can place a die.



Glue stick

For a long time I was using glue stick to mount dies:

  • it can be dissolved with water so it’s easy to remove
  • it doesn’t get dissolved by immersion oil
  • it doesn’t get dissolved by acetone

Preparation

For the chip to be level, it is important to follow this procedure:

  1. Deposit some glue
  2. If your die is not small, spread the glue horizontally and vertically with some flat surface. I use a piece of plastic.
  3. Place the die on it, gently, make sure it doesn’t flip over.
  4. Press the die using the side of a little piece of cardboard.
    Alternate between horizontal and vertical, start with borders then press the center.

Check the leveling using high magnification (ex: 20x or 50x objective). If you failed the levelling, dissolve the glue with some water and try again.

Leave to dry for some time. Usually I wait at least one hour, but it depends on the amount of glue and the die size.

Do multiple chips at once to save time.

Cleaning

You can clean the die by rubbing it with a q-tip/cotton swab and acetone. Acetone will not dissolve the glue.

Each time you use immersion oil, clean the die with acetone before and after.

Before, because you don’t want dust to contaminate the oil (and therefore, the objective). After so you can store the die without contaminating the rest. It also prevents dust from sticking to it.



Important notes

Some dies really have a fragile surface. This is the case for yellow polyimide, but also most motorola chips, or if you managed to remove the polyimide layer on some chips.

In this specific cases it’s not recommended to rub the die, as this could damage top metal or scratch polyimide.


Damaged metal trace of a Motorola CPDS9825


You should also be careful when mounting dies with fragile surfaces using glue stick. You can use a flat piece of plastic to press the die evenly without stressing a specific area, but beeswax is just a better solution in this case.