Epoxy die attach is three steps — dispense the adhesive, place the die, cure the joint — and it is the lower-temperature, more forgiving, lower-cost way to attach a die when the part does not need a metallurgical bond. It stays a clean three-step process only if you know the handful of things each step can get wrong, because every one of them is a parameter that drifts quietly until an inspection catches it.
Dispense
The adhesive is metered onto the substrate before the die lands — by needle, by stamp, or by jet for fine or high-throughput work. The pattern and volume are the design decision here: too little and the fillet does not form or the joint starves of adhesive; too much and epoxy climbs the die sidewall or bleeds out past the footprint. A silver-filled epoxy is chosen when the joint has to conduct heat or current; a non-conductive epoxy when it must not. Both behave differently under the die, so the dispense pattern is tuned to the material, not copied between them.
Place
The die is set into the wet adhesive at a controlled force and speed so the epoxy spreads to a full bond line and a clean fillet without squeezing out. Placement accuracy and the scrub or tack motion matter: a die placed off-axis or tilted sets that error into the cured joint. We place at ±2.5 µm at 3σ on BESI Datacon and Tresky platforms, so the geometry is controlled and captured rather than hoped for.
Cure
The joint is cured on a thermal profile — a ramp, a dwell, a controlled cool — that the epoxy datasheet defines. Cure is where the least-visible failures are set. An under-cure leaves the joint soft and its properties off-spec; too fast a ramp traps solvent and volatiles as voids; the shrinkage and thermal-expansion mismatch that cure locks in is what the joint carries for the rest of its life.
What goes wrong
The failure modes cluster, and each traces to one of the three steps:
- Voids — trapped air or outgassing during cure, worst under large die where the centre is hardest to fill and hardest to inspect. A void is a hole in the thermal and mechanical path.
- Resin bleed and epoxy climb — filler-poor resin wicking out past the die, contaminating bond pads or a seal ring; or adhesive climbing the die sidewall onto the active surface.
- Die tilt and bond-line variation — uneven dispense or placement force leaving one corner thick and one thin, which concentrates stress and skews the thermal path.
- Incomplete cure and outgassing — a soft joint, or volatiles that keep releasing after cure. In a sealed cavity that outgassing is a hermetic problem, which is why organic attach is usually kept out of hermetic builds.
All of these are caught the same way: die-attach void content verified by X-ray when void measurement is required by the part or the specification, plus automated optical inspection and metrology for bleed, fillet and tilt, and cross-section where a programme needs destructive confirmation.
When epoxy is the right choice
Epoxy wins when the part does not need a high-remelt metallurgical joint: lower process temperature, tolerance of a wider range of die backsides, and lower cost. When the part runs hot, has to be hermetic with nothing organic inside, or has to survive downstream reflow, a eutectic attach is the better answer — and the decision usually comes down to the CTE mismatch between die and substrate, which is walked through in solder vs epoxy vs sinter, and why CTE drives the choice, with the direct head-to-head in eutectic versus epoxy die attach.
We run conductive and non-conductive epoxy die attach alongside eutectic, sinter and fluxless systems in Halethorpe, Maryland, on US soil. More on our die bonding services page.
Answered.
What are the steps in the epoxy die attach process?
Three: dispense the adhesive onto the substrate, place the die into it at a controlled force and speed, and cure the joint on a thermal profile the epoxy datasheet defines. The adhesive is dispensed by needle, stamp or jet, and can be silver-filled for thermal or electrical conduction or non-conductive where the joint must isolate.
What causes voids in an epoxy die attach?
Air trapped during dispense and placement, or solvent and volatiles released during cure when the thermal ramp is too fast. Voids are worst under large die where the centre is hardest to fill, and each one is a hole in the thermal and mechanical path. They are verified by X-ray when void measurement is required by the part or spec.
What is resin bleed and why does it matter?
Resin bleed is filler-poor epoxy wicking out past the die footprint and onto neighbouring bond pads or a seal ring, where it can prevent wire bonding or a good seal. It is a dispense-volume and material problem, caught by automated optical inspection.
Is epoxy die attach conductive?
It can be either. Silver-filled epoxy conducts heat and current and is used when the joint has to; a non-conductive epoxy is used when the die backside must be isolated. The two dispense and behave differently, so the pattern is tuned to the chosen material.
When should I use epoxy instead of eutectic die attach?
When the part does not need a high-remelt metallurgical joint. Epoxy runs at lower temperature, tolerates a wider range of die backsides and costs less. Choose eutectic when the part runs hot, must be hermetic with nothing organic in the cavity, or must survive a later reflow. The deciding factor is usually the die-to-substrate CTE mismatch.