What Every PCB Engineer Should Know About PCB Stencils

The world of electronics manufacturing would be considered pretty much incomplete without PCB stencil technology. While printed circuit boards or PCBs have become the foundation for all kinds of electronics devices and applications, stenciling is the catalyst that has made its production process more commercially viable and effective on an industrial scale. So if you are an engineer, it is your utmost duty to know as much as you can about PCB stencils. This blog post will provide you with an initial glimpse.

The process of PCB manufacturing involves application of solder paste on the circuit board or substrate upon which the electrical connections and components will later be placed and secured. This solder paste creates a firm and reliable bond through which electricity will flow, making the PCB functional, thereby getting the electronic device in question to run.    

As an engineer, you will definitely appreciate the challenge that this step of the manufacturing process poses. Whether for a single PCB creation or for industrial scale manufacturing, an engineer needs to ensure that the solder paste goes exactly where it is intended to be on the substrate. Even the slightest straying from the decided path or inadvertent leaks/spreads can cause unintended bridging and faults in the circuit, causing the PCB to fail. PCB stencils are designed and printed to avoid these issues, allowing for accurate, effective and reliable production of circuit boards on a mass scale.

Using PCB stencils in the electronics manufacturing process is quite easy to understand. The stencil is crafted in accordance with the PCB design relevant to the application. For paste application, the stencil is placed on the substrate and the fluid-like solder is squeegeed onto its surface. The pathways and holes in the stencil dictate the exact position where the solder paste needs to be at. The components of the circuit are placed next onto the substrate in a way that the solder paste secures them firmly in place. The stencil is then carefully removed and the process is complete.

PCB stencils have, in a way, improved the precision and effectiveness of the surface mounted technology manufacturing process singlehandedly. The importance of stencils can therefore, never be over-emphasized for a PCB engineer.

Things to Know About Surface Mount Adhesives

Soldering is now the standard method of making an electrical connection in all kinds of electronic devices. The printed circuit boards that are used to set up circuit for these devices are created after much effort. The printed circuit board is an assembly of components which make up a circuit. While setting up a circuit, there is something required to hold the components in place before they are soldered on. Surface mount adhesive serve this purpose very well – it holds all the components in place while soldering is performed.

Surface mount adhesive is highly effective in wave soldering techniques. In fact, it is highly popular in wave soldering. With the transition of soldering techniques from through-hole to surface mount soldering, it became increasingly important to keep the components in place while they are soldered. Just about any glue could not be used for the fear of impurities and oxidation. Surface mount adhesives are a special glue that does not interfere with soldering process.

The interesting fact is that surface mount adhesives are evolving, and have been developed further to be compatible with lead-free soldering as well. In addition to wave soldering, these adhesives can also be used with surface mount technique. Compatibility of these adhesives with liquid fluxes has also been achieved.

Surface mount adhesives can be deposited on the printed circuit board using many methods – jetting, needle dispensing method and stencil printing. Research is still ongoing regarding performance of these adhesives with various fluxes and flux-cored solder wires.

These adhesives have greatly improved accuracy of printing circuit boards. Pasting the components accurately in place ensures error-free connections.

Know When to Use Cored Solder Wire in Your Application

Whether you follow a hand soldering or a robotic soldering process in your PCB manufacturing facility, the importance of flux for the success of your operations and creating reliable solder bonds can never be understated. Flux is necessary to remove impurities from and prevent oxidation of the surfaces being joined together through soldering. Cored solder wires are basically soldering alloy wires with a flux core – that allow for automatic application of flux on the desired surface with minimum chances of oxidation. So, the answer to “When to use cored solder wire in your application?” lies in the amount of efficiency and economy that you are trying to achieve through your PCB manufacturing process.

Cored solder wire, as explained above, is a hollow metal alloy wire with rosin or water based flux in its core. Heating the wire itself will activate its flux core, which has a different viscosity as compared to the alloy and will thus spread on the surfaces in a faster and easier way, thereby forming a protective shield against impurities, contamination and oxidation. The separate step of flux application is eliminated from the process altogether this way.

Using flux cored solder wires, therefore, helps in saving both time and money. It can directly improve the efficiency and productivity of your manufacturing process and ensure a reliable solder bond every time. They have a much higher deposition rate as compared to solid solder wires. Plus, they create strong, reliable solder joints that function exactly as expected. The extra step for flux application is eliminated from the PCB assembly process, thereby making your operations more efficient, faster and economical.

You can choose from no-clean, water soluble and activated rosin flux core types in accordance with your process requirements. These are easily usable for component attaching, rework as well as touch up soldering applications in through-hole and surface mounted tech production operations. The choice is yours!

Effectiveness of Liquid Soldering Flux in Soldering Applications

Flux is a chemical used in soldering, for the purpose of cleaning the surface of printed circuit boards. Cleaning is necessary to prevent oxidation of metal as oxidized metals create problems in bonding and soldering – which makes fluxing the most important activity in soldering. There are many soldering wires available which are cored with flux, so it becomes unnecessary to flux before soldering when cored solder wires are used. However, when there is no flux-cored wire, cleaning surfaces is very important. In this blog, we will discuss the effectiveness of liquid soldering flux in solder metals.

There are many kinds of flux available in the market. The two major categories are rosins and water soluble fluxes. Both fluxes need to be cleaned from the board after application. Rosins require a solvent to get washed, while water-soluble fluxes can be cleaned with water. Liquid soldering flux is majorly used in surface mount soldering processes. It is a precision flux which works well with small components. It can be used with needles, syringes, orflux pens for application onto surfaces, facilitating accuracy in application. This is a necessary requisite which ensures there is no residue after the flux has done its work. Liquid solder has one more colossal benefit over its counterparts – it spreads well. If you are mounting components with high difficulty level of soldering, using a liquid flux will allow you to achieve more effective cleaning as compared to other forms.

Liquid soldering flux is not recommended for through-hole soldering, though, for the practical difficulty of it.

Electronic Solder Paste and the Process of Using It in SMT Assembly

Electronic solder paste is invariably used in both mass SMT assembly as well as prototype circuit board creations. The material becomes one of the most viable solutions for creation of reliable, lasting and cost effective electrical interconnectivity bonds between different surfaces in a circuit assembly. The process followed to create this bond consists of a number of steps and stages. This blog post gives a brief insight to each step, helping you better understand the SMT assembly process and the intricacies involved.

The paste is made up of powdered metal that is mixed with a viscous substance known as flux. This flux usually acts as a temporary adhesive that allows the solder alloy to take position on the PCB surface. The metal in the paste is later melted as part of the soldering process thereby, creating the firm bond needed for circuit assembly.

The process begins with the application of the electronic solder paste onto the printed circuit board. In most manufacturing operations, electronic solder paste is applied to the PCB surface through the stencil with the help of a squeegee. The squeegee blade spreads the solder paste evenly on the surface while the stencil makes sure that the paste reaches only those parts of the circuit where a bond is required.

Once the application stage of the SMT assembly process is complete, the electronic solder paste covered circuit board is passed onto a pick-and-place machine. Here, different components of the circuit design are added to the board which are held in pace by the inherent surface tension of the electronic solder paste. The board is then heated to the solder alloy’s melting point so as to activate the metal in the paste and get it to firmly bond to the surfaces it is supposed to be joining. Subsequent cooling of the board results in the formation of a solid metal joint between surfaces with electrical and thermal conductive capabilities. This bond is reliable, resistant to thermal and mechanical fatigue, and can easily withstand issues like sheering.

And that is how electronic solder paste is used to create solid, lasting surface bonds between different components of a SMT assembly.

Liquid Solder Flux – Its Role in the Circuit Assembly Process

Soldering components together is a key part of the electronics manufacturing process. However, there are many facets that can hamper the bond between circuitry components, causing defects and malfunction in the surface mount device (SMD). An improperly formed solder joint is unreliable, brittle and may even be incapable of surviving through the thermal and mechanical fatigue that it will be subjected to, as a result of everyday use of the circuit. Preventing such occurrences is therefore, a prime concern for PCB manufacturers. Liquid solder flux plays an exceedingly important role in maintaining the integrity of any soldered bond and ensuring high quality of the circuit board produced.

What Does Liquid Solder Flux Do?

The process of soldering requires the formation of a metallurgical bond between two surfaces which chemically react with each other to achieve a stable and reliable bond. This bond is only possible when:

a.    The solder alloy is chemically compatible with the surfaces being bonded together, and
b.    The surfaces are free of any impurities that may physically and chemically hamper the formation of a good bond.

Point (b) in the assembly process is the responsibility of the liquid solder flux. Flux is a chemical that is applied to the surfaces being bonded together before application of the solder paste. Flux reacts with the impurities and contaminants on the circuit surface (particularly oxides, dust and grime) and cleanses the surface of the board so the metal is primed for creating a good solder bond.

How Is Liquid Solder Flux Used?

Oxides are generally formed on circuit board surfaces when the metal they are made of reacts with oxygen. Presence of these oxides can make soldering a virtually impossible job. Application of flux is therefore, a preparatory step in the soldering process whereby the surfaces being bonded are first cleaned and primed with this chemical. The flux remains as a protective layer on the surface of the metal, preventing further oxidation until the soldering process is complete. Soldering, by definition, is a task carried out at high temperatures which are hot enough to vaporize any liquid flux residue on the surface, leaving the metals free and pristine for a proper chemical bond formation. Most SMT assembly processes also follow the practice of pre-heating the metal surfaces prior to solder paste application to prevent any liquid solder flux residue from being left behind.

You can get in touch with Alpha Assembly Solutions to find the type of liquid solder flux and recommended application process that is best suited for your SMT assembly operations.

Solder Stencils – Design Factors to Consider for Perfecting Your SMT Assembly Process

In the world of SMT assembly, solder stencils function as your gateway to a flawless process. Accurate and repeatable solder paste application on the circuit board can only be possible through properly designed and fabricated stencils that precisely follow your assembly specifications. The apertures in the stencil are responsible for dictating how the solder paste will be printed through them onto the circuit board, how well it will hold the SMT components in place and how well it will secure them to the substrate. So clearly, solder stencils are a BIG priority if you are planning to perfect your SMT assembly process. Here are some design factors that you should keep in mind to achieve an exemplary assembly process:

•    The size, shape, thickness and composition of your solder stencil apertures will have a major effect on your assembly process yield. These factors are responsible for how the solder paste will be deposited on the circuit board. Be very careful while finalizing these parameters.

•    During the SMT printing process, the moment when the solder stencil is separated from the substrate happens to be the most crucial. Competing surface tension will determine whether the solder paste will get accurately transferred to the substrate or if it will remain stuck to the stencil aperture walls, thereby ruining the result of your circuit printing. Aperture design is crucial to minimize losses here.

•    It is recommended that the substrate pad area be greater than 66% of the aperture wall surface area. Any lower ratio than this will dramatically decrease the efficiency of your solder paste transfer process, making your circuit print erratic and unusable.

•    Solder stencil design dependability also depends on the technology used to finish its aperture walls. Stencils with laser cut and electro-polished apertures have higher chances of improving the solder paste transfer efficiency of your assembly process.

•    The more miniaturized your circuit design is, the more attention you will have to pay towards solder stencil accuracy and precision. Ultra-fine pitch applications usually require very small amounts of paste deposition on the substrate for completing the circuit print – therefore, deviation of even a fraction of a millimeter can impact your SMT assembly.

Keep these basics in mind when designing and evaluation your solder stencil – it will eventually help you in getting the best results from your SMT assembly process.

PV Ribbon – The Application of Solder Alloys in the World of Photovoltaics

Use of solar panels for electricity generation is becoming a mainstream phenomenon with each passing day. This increased dependence of people and industries on photovoltaic energy generation has necessitated the development of more reliable and high performance components – PV Ribbon being the most important one of them. In this blog post, we will explore the role of solder-coated PV Ribbons in photovoltaic applications and examine the emerging trends in this industry.

A PV Ribbon is an interconnect/tabbing ribbon created as a hot dip tinned copper conductor for installation in solar panels and other photovoltaic devices. This interconnect ribbon wire is directly soldered with the silicon crystals in a solar panel and its function is to carry the electric current generated by the solar cells to the PV bus bar. The PV bus bar also requires the use of the same hot dip tinned conductor for connecting the ribbon with the solar panel junction box. This ribbon wire is usually 1 – 6 mm wide and 0.08 – 0.5 mm thick with a tin/solder coating of 10-30 microns for minimizing copper erosion.

The process of manufacturing PV Ribbon involves annealing and cleaning of copper wires followed by hot dipping them into a solder alloy. The solder alloy used for dipping the copper wires has to be high performing, reliable and capable of effectively preventing copper erosion in accordance with the photovoltaic industry standards. Another important consideration here will be minimized oxide formation or drossing of the alloy during the coating process.

Tin-Lead based alloys have long been the material of choice for coating PV ribbon capable of matching the needs of photovoltaic applications. However, the introduction of the RoHS directive has necessitated the complete avoidance of lead based solder alloys – an industry development that is now leading alloy manufacturers towards developing lead-free alternatives. Alpha Assembly Solutions has been a pioneer in this field, bringing forth a revolutionary product known as ALPHA® EcoSol – a lead-free and low melting point solder alloy that offers performance attributes that are comparable with tin-lead alloys, is cost effective and is specifically designed to meet the needs of PV Ribbon Tinning and cSi Module Assembly. You can trust this product for your photovoltaic manufacturing requirements.