WHAT IS SOLDER DROSS AND BENEFITS OF RECYCLING IT?

With the growing need for sustainable manufacturing practices, industries are looking to reduce their dependence on scarce natural resources and attempting to optimize existing processes for better use of materials being consumed. This trend towards eco-friendly operations has also touched upon the electronics manufacturing industry where changes are being made to ensure proper utilization of solder metals being used and prevent wastage from occurring. This is how solder dross and the benefits derived from recycling it have come to light.

What is solder dross?

Wave soldering processes are usually carried out in the presence of air, owing to which there are always chances of the metal alloy being rendered unusable because of oxidation. This unusable alloy is known as solder dross which is usually thrown away as process waste. In reality however, dross is more than 75% pure alloy, which just needs processing and refining to render it reusable again. The process of recycling solder dross, removing its inherent impurities and contaminants and making it pure enough for reuse in PCB assembly process is therefore, needed to make electronics manufacturing and assembly more sustainable and eco-friendly.

What are the benefits of recycling it?

The most obvious benefit of recycling solder dross is the reduced strain on the Earth’s natural resources. When manufacturing processes are optimized for maximum consumption of raw materials through dross recycling, the need for further mining of natural ores is reduced drastically, thereby making these operations easier on the planet. Dross recycling offers additional revenue to the manufacturer as the unusable solder waste can be sold off at reasonable process to recycling companies. The process also helps reduce the amount of electronic waste that makes its way into landfills and garbage dumps in the form of solder dross. Overall, it offers a win-win situation for all stakeholders involved in the PCB manufacturing process.

THREE MAIN FUNCTIONS OF LEAD (PB) SOLDER PASTE

Lead solder paste is essentially a well-engineered mixture of a flux, which acts as the medium, and a solder powder. There is not just one kind of solder paste; since it can be engineered, it can be made to display any rheological property by changing the flux and the metals in the solder powder. For different soldering applications, a different consistency of flux is required. Here are three primary functions of lead (Pb) solder paste.

Function #1: Cleaning
Solder paste, with liquid flux as a medium, is semisolid and has another very important function – to clean the area of oxides. Stenciling typically deposits solder paste over the intended areas only, therefore cleaning achieved is also very accurate and effective.

Function #2: Adhesion

Solder paste application on a printed circuit board is also intended to act as an adhesive to hold the components in place until the board is heated to start soldering. Solder paste is capable of keeping the components immobile until a connection is forged.

Function #3: Connection

Solder paste consists of metals that assist in bonding of two surfaces. When heated during soldering, the solder paste melts and achieves a mechanical and electrical connection on the board between the intended components.

Solder paste is an integral part of soldering process and should be executed with care and precision if an effective bond is to be achieved and soldering defects avoided.

A QUICK INTRO GUIDE TO THE PCB ASSEMBLY PROCESS

Manufacture of printed circuit boards is a highly complex process, which does not look very difficult on the surface. However, it actually requires high attention to detail if a good printed circuit board is to be produced. All the surface mount components to be placed on a circuit board need to be assembled and soldered in precision. This blog is designed to provide you with a quick introduction to the PCB assembly process.

Step #1: Solder stencils

In the first step, a stencil is placed over the circuit board. Stencils help in application of solder flux and paste to the areas where soldering is to be done. Stencils are used for precision works.

Step #2: Placing

Back when mechanization of processes was still a thing of the future, placing the surface mount components onto the board after fluxing was done manually. However, today, machines do all the component placement work, and everything is automated. PCB designs are fed into computers which then run the pick and place machines.

Step #3: Reflow

After placing the components onto the board, the job is to keep them at their designated places. This is achieved by passing the board through a reflow oven, wherein the PCB is heated to temperatures higher than 200°C. This melts the metal in the solder paste. Further ahead in the oven there are cooler heaters which work to solidify the molten metal in the paste. This controlled heating and cooling ensures that all the surface mount PCB components are permanently joined with the board.

Step #4: Quality examination

Checking placement and connection errors is a necessary step in the manufacture of PCBs, otherwise all the exercise above would have been for naught if the boards were to come out faulty. The checks can be manual or automated.

Assembly of PCB can be done in many ways. Manual assembly is time consuming. Automated process, if maintained and run well, is always better.

SOLDER: WHAT IS IT AND HOW TO USE IT

Electronics are the stars of this time and age. Daily routine seems impossible to go through without the everyday conveniences that various electronic devices make possible. The electronics industry today is one of the most thriving and happening industries in the world. Thanks to a certain technique that makes it possible to develop devices that can do practically anything, now the populace can sit back and enjoy the fruits of all of it. This technology is soldering. In this blog, you will learn about this revolutionary technique and the soldering materials that have changed the way electronics are perceived in this world.

What is solder?
Solder is typically an alloy used to create an electrically conductive bond between two metals. This alloy makes fusing two metals possible by melting and connecting the two surfaces. In order for this bond to be permanent and efficient, it is necessary for the connection surfaces to be clean and free of oxidation. There are many types of soldering materials available in the market, so that you can choose the one best suited for your needs.

•    Lead solder – This solder is composed of tin and lead, and is one of the most commonly used solders out there.

•    Flux-core solder – this solder is packed with convenience. It has flux material at its core so the users don’t have to apply it prior to soldering.

•    Hard solder – these solders are typically made from copper fused with either zinc or silver. This alloy melts at high temperatures and is used for brazing.

•    Lead-free solder – this solder is an alloy that was developed to be lead-free and environment friendly. These alloys are made up of bismuth, indium, coppers, silver, etc.

How to use solder?
Solders are usually available as coils of solder wire. After you have heated up and cleaned the soldering iron, touch the solder wire to the tip of the iron and tin it – it helps achieve a better soldered joint. One can also find solder spheres in the market. To use solder balls, you need a stencil and flux paste. Alternatively, you can employ BGA JIG that already have embedded solder balls. If any of the above solder use is not suitable for your process, you can also employ fully automated machinery.

MATERIALS AND TOOLS NEEDED FOR SOLDERING

Soldering is one of the most commonly used methods to fix components on a board while assembling an electronic circuit. The process is time-tested and, if used effectively, can create highly reliable, strong, resilient and electrically conductive joints between surfaces. So, if you are currently working on a circuit assembly, you will need a host of materials and tools in order to achieve proper joints between components and surfaces. This blog post provides you with a list of soldering materials and tools that you will need for your circuit board assembly process.

For soldering, you will need:

• Soldering iron for heating the solder wire for making it wettable so that it can be applied to the surfaces to be joined to create a connection between them.

• Solder wire, which is basically a thin strip of appropriate alloy which when heated, becomes the metal filler that connects the two surfaces that are being soldered to each other.

• Flux that will be used to clean the surfaces being soldered as well as the tip of the soldering iron. Its function is to remove impurities, especially oxidation, from the surfaces to ensure the creation of a reliable solder bond.

• Solder balls, in case your circuit assembly involves Ball Grid Array (BGA) packaging.

• Solder paste, in case your circuit assembly requires the use of through-hole soldering for printed circuit boards.

• Tweezers for moving, lifting and placing miniature electronic components that are needed to complete the circuit board with precision.

• Rubbing alcohol or a similar solvent for cleaning circuit board surfaces as well as for removing flux residue after the soldering process is complete.

• De-soldering tools like solder suckers and solder wicks that can help remove excess solder material from the circuit surface. It can also come in handy in case you make a mistake and need to start the soldering process over.

• Wire cutter or shears for cutting solder wires or stripping away the ends of components/wires being joined.

• USB microscope, in case your circuit assembly involves use of fine-pitch components and to discover tiny solder deposits of solder that shouldn’t be there.

• Safety glasses and gloves, for protecting your eyes and skin from the damage that contact with molten solder and solder fumes can cause.

PROS AND CONS OF SOLDER PASTE STENCILS

All electronic devices have a printed circuit board fit into them. It is the most basic component, needed for all electronics to function the way they are meant to. Printed circuit boards are manufactured with high precision, which, today, is made possible through the usage of solder paste stencils. A stencil is a device which is made from a thin foil or filament, which is cut either manually or robotically, in accordance with the design of the printed circuit board. This stencil is especially useful for application of solder paste onto the board, which aids further processes. This blog discusses the pros and cons of solder paste stencils.

Pros
 
•    Stencils are extremely easy to set-up and use. For a mass-manufacturing process, stencils are extremely useful and economical because a single stencil can be reused for multiple solder paste applications.

•    Stencils allow on-contact and off-contact printing on printed circuit boards.

•    Stencils allow usage of a wider range of viscosities of solder pastes.

•    Stencils are extremely easy to clean.

•    Stencils do not plug up easily.

•    Stencils are extremely convenient to use in cases of multilevel printing of circuit boards.

Cons
 
•    Stencils may increase cost of production where the design of circuit boards changes frequently.

•    They require proper maintenance and storage in order for them to keep functioning properly as the material they are made of may bend and disturb the aperture or openings, which may create problems while printing and result in defected products.

Stencils enable a highly efficient production of printed circuit boards. If you own a PCB manufacturing facility, using stencils will be highly profitable for you.

SMT & SMD APPLICATIONS OF SOLDER PASTE

For those who are new to the world of electronic assembly, solder paste is that grey goo-like material that comes in a tub or tube and has the consistency of cake frosting. For those who want to get into the details of this substance, solder paste is power metal solder that is suspended in a thick viscose medium known as flux. This medium does two things – it holds together the components that are being soldered and it scours the surfaces of impurities to ensure that a strong and reliable solder joint is formed between them. Let’s explore solder paste further and understand its application in SMT and SMD processes.

Applications of solder paste

Solder paste is extensively used in industrial scale for SMT and SMD production where accurate application of solder alloy to components needs to be managed efficiently and effectively. It is especially advantageous for miniaturized circuit assemblies that are used in handheld electronic devices like smart phones, tablets, computer motherboards, military electronics, automotive systems, medical equipment and more. It is also used in through-hole, pin-in-paste components where the paste is applied and spread in/over the holes in a printed circuit board with the help of a squeegee. This flux medium, being sticky, holds the components in place while the PCB is heated or baked till the metal components in the solder paste melt and form strong mechanical and electrical joints between intended surfaces.

Composition of solder paste

The composition of solder paste varies based on the properties expected from it for the specific SMT and SMD processes where it will be used. For example, soldering plastic component packages to glass epoxy circuit boards requires the use of solder paste with Sn/Pb or Sn/Ag/Cu compositions. High shear strength requirements are suitable to Sn/Pb combination alloys. The solder melting temperature suitable for a particular PCB assembly process also has an impact on which solder paste will work best for your requirements. Solder paste also differs in accordance with the size of the alloy particles that are suspended in the flux paste. The specific features of your PCB printing process and print quality expected from the paste will determine the metal particle size that will best work for your application. The type of flux medium used in the paste (rosin based, water soluble or no-clean) also categorizes the product, again impacting the way your PCB printing and manufacturing process will work.

Hope this information helps further your understanding of solder paste and its importance in the world of PCB manufacturing.