Editorial Team - PCB Directory
May 18, 2021
Eutectic solder is a type of solder that melts and solidifies at one single temperature. For example, Tin 63% / lead 37 % that melts and freezes at 183°C (see figure below). Most solder starts to soften at a certain temperature and only fully melts at a higher temperature. For instance, the Sn96.5Ag3Cu0.5 solder starts to melt at 219°C (426.2°F), but only reaches its full liquid state at 221°C (429.8°F).
So any solder alloy that melts and solidifies at one single temperature is called Eutectic solder. When we change the composition from Tin 63% / Lead 37% to Tin 60% / lead 40%, then the melting point becomes a melting range. The solder alloy having a melting range is known as non-eutectic solder.
What is the advantage of Eutectic Solder?
Since Eutectic solder melts and solidifies at a specific temperature, it is better for the solder reflow process than non-eutectic solder. It speeds up the solder reflow process which results in a faster PCB assembly process and a higher throughput which in turn lowers the effective cost of PCBs.
Other advantages include:
A list of a few Eutectic Solder materials can be seen in the table below.
Lead-free Eutectic Solder Composition
Solder Alloy composition
True eutectic determined by National Institutes of standards and Technology (NIST)
US NEMI consortium recommends this solder for reflow soldering. Used in BGA balls.
Specifically designed to replace the lead solders in copper and stainless steel plumbing.
Used in photonics device and cryogenic applications
Very high strength. Used for die attachment
Zinc - Aluminium
Used for Soldering aluminium.
Tin – Zinc
Specifically used in Aluminium to Aluminium and Aluminium to copper soldering.
Indium – Tin
Suitable for low temperature soldering.
Bismuth – Tin
Extensively used in through-hole technology assemblies in IBM mainframe computers.
How do you select eutectic solder composition?
There are various compositions of eutectic solder available. Choosing the right composition for an application is based on several factors. But, the solder melting point of the process at hand is the main factor to consider.
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