Friday is here again, and with it the weekly "A Taste of Physics" column — number 36.
This week: melting points, eutectic mixtures, and the special properties of tin.
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The video shows a mixture of tin and lead, an alloy commonly used for soldering electronic circuits.
The numbers represent the percentage of tin relative to lead.
As you can see, a ratio of 63% tin to 37% lead delivers the best results.
To understand why, we first need to understand what a melting point is and how it affects the soldering process.
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The melting point of a substance is the precise temperature (at one atmosphere of pressure) at which the substance exists on the boundary between solid and liquid.
At the melting point, adding energy will melt the substance into a liquid, while removing energy will turn it back into a solid.
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A material used for soldering must have a melting point lower than that of the electronic circuit it is being soldered to.
If their melting points were equal, the electronic circuit itself would also melt during the process and be damaged.
Tin's melting point is considered low (232°C), which means it can be melted without harming the electronic components on the board.
Tin is also well suited to the task because it is a good electrical conductor, protects against corrosion, and bonds well to other metals.
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The addition of lead is intended to turn the tin into a eutectic mixture.
A eutectic mixture is a mixture of two substances at a specific ratio at which their combined melting point is at its lowest.
In this case, for example, adding 37% lead to tin lowers its melting temperature from 232°C to 183°C.
In addition, the lead makes the mixture more stable and flexible, and since it is also inexpensive, it reduces the overall cost of the alloy.
Shabbat Shalom 😊
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