NOTE ON SAW FLUXES
1. BASICITY OF THE FLUX:
Basicity is ratio of Basic oxides to Acidic oxides present in the flux. For the basicities mentioned in AWL literature, formula devised by Boniszewski is used, which is as below:
Basicity =
CaO + MgO + CaF2+ NaO + K2O + ½(MnO + FeO)
———————————————
SiO2+ ½(Al2O3 + TiO2 + ZrO2)
Activity of the flux is devised by Wall Neutrality Number. Wall Neutrality Number is measured as below:
- Make two chemistry pads with same wire flux combination, same welding
parameters, except voltage used for 2nd
pad is increased by 8V. - They are analyzed for Si and Mn.
- The wall neutrality Number is
calculated by following formula:
Wall Neutrality Number = 100 ( |Δ % Si|
+ |Δ % Mn|)
Δ % Si – Difference in Si in two pads
Δ % Mn – Difference in Mn in two pads
Wall Neutrality Number is absolute
value, ignoring positive and negative
sign.
Based on Activity, Fluxes are divided into following types:
- A. Active Flux – Wall Neutrality Number >35
- B. Neutral Flux – Wall Neutrality Number ≤35
Recommended cycle for flux re-drying: 300-350 C for minimum 2 hrs.
