What are the disadvantages of lead-free solder vs. lead solder?

Most electronics use solder to attach components to printed circuit boards (PCBs). Traditional solder is made of lead and tin. For many years, this mixture has been the standard used across the electronics industry.

In the recent past, concerns have been raised about the health and environmental effects of leaded products. Lead is poisonous and it can build up in the body due to repeated exposures. It is hazardous waste and can contaminate soil and ground water.

In 2006, the EU implemented the Restriction of Hazardous Substances directive. This directive limits the use of lead solder in electronics produced in the EU.

What are the differences between them?

Lead solder is a mixture of 60% tin and 40% lead (or 63/37). It is popular thanks to its low melting point (183°C). They are easy to work with, flow well and form strong bonds with other metals.

Lead-free solder formulations have a varied percentage of metals. Components can include tin, copper, silver, nickel and zinc. The most common lead-free mix is tin-copper, which has a melting point of 217°C. Lead-free solders have properties that are distinct from traditional lead-tin mixes. Manufacturers often need to adjust to these peculiarities by making design and process changes on products.

What are the disadvantages of lead-free solder?

The higher melting point and different composition of lead-free solders have several side effects.

• High melting point: Most lead-free replacements for leaded solder have higher melting points. This oxidizes the solder quickly. It can also lead to component stress.  Components with plastic package or electrolytic capacitors will be more affected. Electronics with low dielectric constant may be vulnerable to failures.
• High cost:  It is cost-effective, compared to lead-free. Lead is about ten times cheaper than tin. Thus, a higher tin content means a higher product cost. Some lead-free solders contain silver, which is expensive.
• Low wettability: Lead-free solder does not flow as well as lead-based solder. It undergoes wetting slowly.  Joints tend to be less effective in self-regulation ability, tensile power, and shear capacity.
• Formation of deposits:  Lead-free solder forms surface oxides, flux impurity and alloy deposits. These can impair component performance. Proper maintenance is required to prevent and remove deposits.
• Formation of tin whiskers: Lead-free solder has high tin levels. This can create tin whiskers between adjacent pins. Tin whiskers are thin, conductive structures a few millimeters long growing away from a metal surface. They can cause short-circuits and electronic system failures.
• Formation of metal dendrites: A problem similar to the one described above. A dendrite is a tree-like structure of crystals growing as solder solidifies. Dendrites lead to malfunctions and failures.

To prevent such problems, manufacturers have developed several types of lead-free solder with unique properties. Among them are:

1. Tin-Silver:  Silver reduces oxidization and improves conductivity. Tin serves as a base metal, providing strength to the solder.
2. Tin-Copper: Copper improves mechanical strength and improves conductivity.
3. Tin-Zinc: Zinc lowers the melting point of the solder. It is also a cost-effective material.

Leaded and lead-free solder products

ConRo Electronics, as an electronic manufacturing and soldering systems distributor, offers a wide choice of Leaded and lead-free solders, from major manufacturers such as Indium and Surclean.

We’ll show you how to improve product reliability while increasing performance and lowering costs. Our team of technical support specialists will provide your company with dependable global supply, unrivalled efficiency, and superior technical support.

Feel free to contact us on 0208 953 1211 or send us an email to info@conro.com