An IPC cleanliness designator (defined in IPC J-STD-001) is sometimes called out on assembly drawings. A common designator is C-22.
The first number indicates the number of board sides that must be cleaned
0 – No cleaning required
1 – Solder side only must be cleaned
2 – Both sides of the board must be cleaned.
The second and following numbers define the types of cleanliness tests to be performed:
0 – No test for cleanliness required
1 – Test for rosin residues – Used when high solids rosin fluxes are used in assembly.
2 – Test for ionic residues – This is a basic inexpensive test to detect insufficient cleaning.
3 – Test surface insulation resistance (SIR) – This test exposes the assembly to high temperature and humidity to accelerate failure mechanism that lead to shorts.
4 – Test for other organic contaminants – Type and amount of residue is measured, usually using a spectrometer. This is an expensive test.
5 – Other tests requested by client – Any other testing beyond tests #1 – #4.
It is permitted to call out any combination of test types. If both sides are to be clean and all tests to be performed, the cleanliness code would be C-212345.