Challenges of soldering heat dissipating elements

High-copper metallized components and PCBs act as heat sinks: they create a heat dissipation effect that draws heat away from the soldering tip, making it difficult to deliver to the solder point.

17.11.2021
 

In consumer and industrial electronics, solders made of tin, silver and copper (SAC) alloys have become the industry standard for lead-free soldering. In combination with multilayer PCBs and components made for heat dissipation based on metallized lead frames, today's electronics require special, powerful solutions for manual soldering.

Metallized components and PCBs act as heat sinks: they create a heat dissipation effect that draws heat away from the soldering tip, making it difficult to get it to the solder point. To better understand the heat dissipation effect, think about a large copper pan - if the heat is applied to one small point in the pan (the equivalent of a soldering iron tip to a copper sheet) it spreads until the entire pan is hot enough for cooking.

Similarly, the heat dissipation effect makes soldering difficult by drawing heat away from the soldering tip, which requires a special solution to heat both the component and the PCB and consequently melt the solder.

The heat dissipation effect is visible with high power transistors such as TO-220, as well as multi-layer printed circuit boards and PCBs with large, metallized ground planes. Another type of PCB that exhibits a heat dissipation effect is the insulated metal substrate (IMS), commonly used in LED lighting and other applications that generate significant amounts of heat. They are created by applying layers of conductive and non-conductive adhesives to a metal plate, effectively removing heat from components that generate large amounts of it. However, manual soldering of IMS boards can be extremely difficult due to their massive metal backing.

 
 

Other components difficult to solder

RF shielding (often in the form of metal cans), coaxial cables with a metallized earthing or electronics embedded in glass are other items on the list of the 10 most difficult to solder components. Bonding electronics and glass (such as windshield defroster electronics), RF shielding, and grounding are typically made of metals that conduct heat very efficiently, act as large heat spreaders, and are particularly difficult to solder.

Compensation methods and potential risks

To overcome the problems inherent in brazing metallized components and PCBs, operators try to compensate for heat dissipation by extending the time to apply the heat source, i.e. the tip. You can also try to increase the temperature of the tip. These compensation methods not only shorten the life of the tip, but can also compromise reliability or damage both inserts and components.




Burnt solder caused by excessive heat input

Source: Inductive Soldering for High Thermal Demand Applications. © OK International

Another method of compensation is to preheat the PCB and try to solder the component while the PCB is still hot. This, in turn, is not safe for the operator himself, who often have a tendency to keep their face close to the PCB and sometimes rest their hands on it, which causes discomfort at work and may even result in a painful burn.

Induction soldering and resistance soldering

Induction brazing offers a number of advantages over resistance brazing, in particular, the generation and transfer of heat is fast, efficient, repeatable and accurate. Induction soldering irons use an induction coil wrapped around a magnetic core. When alternating current flows through the coil, a field is created that generates heat. With induction heating, the temperature of the magnetic core is controlled by the current flowing through the coil around it. Induction heating is more efficient and easier to control than resistance heating and only allows temperature to be reached when it is needed in the process ('on demand').

In induction soldering irons, the heater and temperature sensor are built directly into the soldering tip, creating a closed heat exchange circuit that is fast, efficient, repeatable and accurate.

Resistance soldering irons heat the entire tip by conduction. Utilizing resistance heating technology, the tip acts as a heat reservoir, with higher thermal resistance and lower thermal efficiency than induction heating. This means that it heats up slower and it is more difficult to maintain a constant temperature of the soldering tip without dangerously exceeding the temperature.

Resistance soldering irons with less efficient heat transfer properties will require higher temperatures to achieve the same result while risking potential damage to components and circuit boards.

The benefits of induction brazing

With today's delicate and complex electronics, accuracy and temperature control are a constant challenge. Metallized components and printed circuit boards combined with temperature-sensitive electronics and the need for lead-free soldering create a complex complex of process control requirements.

To meet these challenges, manufacturers can use high performance induction brazing systems. Induction brazing produces heat 'on demand' quickly and efficiently. And because induction brazing produces heat in a precise and controlled manner, it can be used for the smallest and delicate components as well as for demanding components with high heat capacity.

Summary

Electronics keep getting smaller, faster, smarter and more functional. As the size of the systems becomes smaller, more and more heat is generated in smaller spaces. To aid in heat dissipation, designers use well-conductive materials such as glass and metal in their designs. Lead frames, multilayer PCBs, metallized substrates and grounding surfaces will continue to be widely used, which will require proper soldering solutions.

While resistive soldering systems are evolving towards using more power by producing and transferring more heat to the soldering tips, induction soldering systems take a different approach.

Using a standard power supply and increasing the power frequency around the magnetized core turns out to be a much more efficient way to generate and keep the tip warm.

Source: Inductive Soldering for High Thermal Demand Applications. © OK International & https://tek.info.pl

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