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What Is Solder Mask - PCB Manufacturing & Assembly

Posted:02:37 PM November 15, 2022 writer: NextPCB

Solder melting Point is worth considering as soldering is an essential feature in the PCB industry. Without the application of Solder on Printed Circuit Boards, components would fall off the circuit board leading to design failure.

A Solder joins two or more components on the circuit board firmly. Also, the Solder melts upon heating and resolidifies when cooled upon application. This guide provides details regarding solder melting point.

What is the Melting Point of Solder

Solder is a metal alloy comprised mostly of Lead and Tin. Typically, the melting point of solder could range from 90ºC to 450ºC. These differences are due to varied alloy compositions in the Solder.

However, due to the varied applications of Solder in the PCB industry, solders consist of other alloys of metals such as copper, Silver, Antimony, and Zinc. This different combination of metals gives rise to differences in the melting points of Solder.

Here is a Table that shows the different alloy compositions of Solders and their melting point ranges that are common in PCB manufacturing.

Solder Alloy Compositions (% weight) Metal Composition Range of Melting Point (°C)
95.5% Sn/3.5% Ag/1% Zn Tin-Silver-zinc 218°C – 221°C
95% Sn/5% Ag Tin-Silver 221°C – 240°C
96% Sn/4% Ag Tin-Silver 221°C- 225°C
97.5% Sn/2.5% Ag Tin-Silver 221°C – 226°C
97% Sn/2% Cu/0.8% Sb/0.2% Ag Tin-Copper-silver 226°C – 228°C
97% Sn / 3% Cu Tin-Copper 227°C – 300°C
95% Sn /5% Sb Tin-Antimony 232°C – 240°C
91.5% Sn /8.5% Sb Tin-Antimony 232°C – 240°C
95.6% Sn/ 3.5% Ag/ 0.9% Cu Tin-Silver-copper 217°C
95.5% Sn/ 3.9% Ag/ 0.6% Cu Tin-Silver-copper 217°C
97% In/ 3% Ag Indium –Silver 143 °C
65% Sn/ 25% Ag/ 10% Sb Tin-Silver- Antimony 233°C
95% Zn/ 5% Al Zinc - Aluminum 382°C
91% Sn/ 9% Zn Tin – Zinc 199°C
58% Bi/ 42% Sn Bismuth – Tin 138°C

Types of Solder Melting Point

Solders used in Printed Circuit Board Manufacturing are in two categories based on their melting points. They are:

  1. Eutectic Solder
  2. Non-Eutectic Solder

Eutectic Solder

Eutectic Solder melts and solidifies at a single temperature. It means that the alloy compositions of the Solder melt at a particular temperature and cool down at a specific temperature.

Non-Eutectic Solder

Non-Eutectic Solder cannot melt nor solidify at a given temperature. These alloys of metal require melting at temperature ranges. This Solder starts to melt when it reaches its minimum melting point. It continues to melts until it reaches its maximum melting point, thereby becoming molten (liquid form).

Types of Solders

The following types of Solder used in PCB manufacturing and assembly process include

  1. Lead-based Solder
  2. Lead-free Solder
  3. Flux core solder
  4. Silver Alloy Solder

Let's consider them one at a time

Lead-based Solder

In this type of Solder, Lead is significant in its alloy composition. As such, Lead is usually mixed with other metals to form alloys to reach higher solder melting point. The composition also improves other physical properties of the Solder, like Tensile and Sheer Strength.

The standard type of Lead-based Solder is a mixture of Lead and Tin. Their alloy composition is about 60% Tin and 40% Lead. This Tin-Lead Solder melting point is around 180°C to 190°C, with Tin being the cause of its lower temperature. However, Tin makes up for it with better tensile strength.

Lead-free Solder

Lead harms the environment and human health. While lead-based alloys started the solder revolution in PCB electronics, environmental regulations restricted the inclusion of lead in electronics design. As a result, several compositions of Alloy became lead-free.

In the United States, PCB manufacturers that utilize lead-free solders get considerable tax benefits. As a result, there are incentives from the government to own and apply lead-free solders in the PCB Industry.

Generally, Lead-free have higher solder melting points than lead-based.

Flux core solder

Flux core solder is a spool of wires around a cylindrical device. At its core, there is a reducing agent. During the soldering process, the flux is released, which removes the oxidized layer formed on the metal surface upon contact.

This process allows a cleaner surface and electrical connection. It also improves the wetting properties of the Solder. Under the flux core solder, there exist two different types of Solder: Acid core and Rosin core solders.

Acid Core Solder

The core of this Solder is an acid-based flux which is aggressive and strong in removing the layer of metallic oxide formed on the metal surface. Its joints are solid and do not break.

Acid core solders are helpful for welding steels and other metals. Also, they are applicable in plumbing to join copper pipes together. However, cleaning the flux residue after soldering is crucial to prevent corrosion.

Rosin Core Solder

While the Rosin core solder is similar to the Acid core solder, its difference is that it uses mild flux rosin as its core. Rosin residue does not cause corrosion which earns it an excellent advantage over Acid core solder.

It is commonly applied in soldering electronic components on Printed Circuit Boards.

Factors To Consider when choosing the best Solder.

While your choice of Solder may vary according to the process you want to utilize soldering, here are some prevalent factors to consider when selecting the best Solder.

Subsequent Thermal Process

In PCB assembly, your PCB may require a reflow process after applying a paste mask on the circuit board. This process requires heating the PCB to a higher temperature. Hence, there is a need to use a higher solder melting point.

However, if there is no need for subsequent heating of your PCB, you can choose solders with lower melting points.

Use of Lead of No-lead Solder

While Lead-based solders set the trend in the electronic industry, heavy EU regulations on using Lead are rising. They could bring several lawsuits if you use lead-based Solder. When considering the kind of Solder you want to use for your printed circuit board, ensure you use lead-free solders or other alloy solders that are free of lead.

Application of solder flux

Flux helps clean the surface area that needs soldering, making it easier to sell on a clean surface and ensuring proper solder joints between components. Rosin core flux is enough If your manufacturing process does not exceed printing circuit boards.

However, suppose your design prices range depending on the customer. In that case, it is necessary to have several kinds of solder flux in your manufacturing space.

Conclusion

As this guide has shown, Solder is an essential process in design and manufacturing, especially in the PCB industry. Based on their alloy composition, these solders have varied melting points. Some have their melting point set at a given temperature (Eutectic), others at temperature ranges (non-Eutectic).

It would help if you considered the needs of your PCB and discern what kind of Solder you need (Lead-based or lead-free), the required solder melting point, and the type of solder flux applicable to your process.

At NextPCB, we offer reliable PCB services and solutions to provide you with the best PCB designs for your electronics. In maintaining global PCB standards and compliance with EU regulations, we strive to use safe materials for the environment and your health.

Tag: Solder
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