Solder has a ceiling that is easy to miss on a datasheet. It is not about how well the joint conducts heat — it is that a solder joint's own melting point sets the temperature the finished part can survive, and the margin between "operating hot" and "the attach layer softens" is smaller than most thermal budgets assume. Silver sinter exists to remove that ceiling.
The one thing that makes sinter different
Sinter does not melt. Fine silver particles are consolidated under heat, and optionally pressure, at temperatures far below silver's melting point — and the resulting joint is silver, so its own survival temperature is far above the temperature that formed it.
Every solder or eutectic joint is the opposite: you form it by melting, so the finished joint cannot be taken back near its own formation temperature without consequence. That single asymmetry is the whole argument, and everything else about sinter follows from it.
What that buys
Operating temperature headroom
The direct consequence. A sintered joint keeps its mechanical and thermal properties at temperatures where a solder joint is creeping. For a device that runs hot continuously — power switching, RF at real output, anything with a duty cycle that never lets the die cool — that headroom is the difference between a part that ages gracefully and one that walks toward a failure mode.
No intermetallic ageing
Solder joints change over their lives. Intermetallic compounds grow at the interfaces, and they grow faster hot; the joint you qualified is not quite the joint you have three thousand hours later. A sintered silver joint does not have that mechanism to worry about in the same way — it is one material against metallised surfaces, not an alloy system in slow motion.
Thermal conductivity
Sinter conducts heat well — as an industry generality, substantially better than solder alloys and far better than filled epoxies. This is usually cited first and it is the least interesting advantage, because plenty of builds have thermal paths that solder already satisfies. Buy sinter for operating temperature, and take the conductivity as a bonus.
What it costs
Surface preparation stops being negotiable. Sinter wants clean, properly metallised surfaces on both die and substrate, and it is less forgiving of contamination than a fluxed solder process that can chemically clean as it reflows. If the die backside metallisation is not right, sinter will tell you.
Pressure-assisted sinter adds tooling and cycle time, and constrains what geometries are practical — a pressure fixture has to reach the die. Pressureless formulations relax that, at some cost in the density of the finished joint. That trade is a real engineering decision, not a formality.
When solder or eutectic is still right
Most of the time, honestly. If the part's operating temperature sits comfortably inside what solder tolerates, and the thermal path is adequate, then a eutectic or solder attach is the lower-risk, lower-cost process with decades of qualification behind it. Choosing sinter for a part that never gets hot buys process complexity and no performance.
The question that separates them is not "which conducts better" — it is how hot does this part actually run, continuously, in the worst case its mission profile allows. If that number is comfortable, use solder. If it makes you check a solder datasheet twice, that is the signal.
How the joint gets verified
Die-attach void content is verified by X-ray when void measurement is required by the part or the specification, alongside automated optical inspection and metrology. Cross-section and failure analysis are available where a programme needs destructive confirmation. Placement is captured per unit at ±2.5µm @3σ, so the geometry is auditable after the fact rather than asserted.
Where to start
Two numbers and one fact decide this:
- Worst-case continuous junction temperature the part has to hold.
- How long it has to hold it — a duty cycle that never lets the die cool is a different problem from an occasional peak.
- What metallisation is on the die backside and the substrate, because that is what decides whether sinter is straightforward or a development exercise.
We run pressure and pressureless silver sinter alongside eutectic, epoxy and fluxless attach — four families rather than one house default. More on all of them on our die bonding services page, and the neighbouring decision is covered in eutectic versus epoxy die attach.
Answered.
What is silver sinter die attach?
Silver sinter bonds a die using fine silver particles consolidated under heat, and sometimes pressure, at temperatures well below silver's melting point. The finished joint is silver, so it survives temperatures far above the one that formed it — unlike solder, which is formed by melting and therefore cannot be taken back near its own formation temperature.
Is silver sinter better than solder for die attach?
For parts that run hot continuously, usually yes. Sinter holds its properties at temperatures where solder creeps, and it avoids solder's intermetallic ageing. For parts whose operating temperature sits comfortably inside what solder tolerates, solder or eutectic is the lower-risk and lower-cost answer with more qualification history behind it. Operating temperature is the deciding question, not thermal conductivity.
What is the difference between pressure and pressureless silver sinter?
Pressure-assisted sinter applies force during consolidation, which produces a denser joint but requires tooling that can physically reach the die and adds cycle time. Pressureless formulations remove the fixture constraint and suit more geometries, at some cost in final joint density. We run both.
Does silver sinter need special die metallisation?
It is less forgiving than a fluxed solder process, which can chemically clean as it reflows. Sinter wants clean, properly metallised surfaces on both the die backside and the substrate. If the metallisation is not suitable, that shows up as bond quality — so it is worth settling before the build, not during it.
Who offers silver sinter die attach in the US?
We run pressure and pressureless silver sinter in-house in Halethorpe, Maryland, on US soil, alongside eutectic, epoxy and fluxless die attach. Wafer sizes run 2 in through 12 in including thin and fragile die, across die-to-wafer, die-to-die, die-to-substrate and die-to-PCB configurations.