Shhhh. Don't tell anyone but I have a secret. The activators used in halogen-free solder pastes aren't as effective as their halogen contained counterparts. The real secret is coming up with a technology that overcomes the deficiency. Indium Corporation's approach to this has been to focus on the oxidation barrier of the solder paste. The theory here is that if you can prevent oxidation from occurring through the preheat and soak stages of the reflow process, then the activators have to work less to remove oxides. Indium Corporation used this approach in developing the Indium8.9HF solder paste. This solder paste clearly outperforms most solder pastes in reducing head-in-pillow and graping defects by preventing oxidation.