Loctite FP4531 Underfill

HYSOL®FP4531: Snap Cure, Fast Flow Underfill

Hysol® FP4531 is a fast flow material for flip chip and CSP underfill applications with a gap of 1 mil or larger. The material is designed to snap cure within 7 minutes at 160°C, even with a preheat application temperature as high as 90°C.


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Frozen storage at approximately-40°C, or lower is required for maximum shelf life. Allow material to reach room temperature before use. For best results in dispensing, a 21 gauge needle should be used at 10 psi pressure. For best flow rates, a preheat temperature of 90°C is recommended.

Cure Schedule

Use suggested cure conditions as general guidelines. Other cure conditions may yield satisfactory results.

Recommended Cure: 7 minutes at 160°C

With all fast cure systems, the minimum required time for cure depends on the rate of heating. Conditions, where a hot plate or heat sink is used, are optimum for fastest cure. Cure rates depend on the mass of material to be heated and intimate contact with the heat source.