Understanding the Concept of Electrical Reliability

Soldering is a process that establishes an electrical connection between two components on a printed circuit board. How effective this connection is ultimately depends on the quality of solder and the soldering process. A good solder joint has a good electrical reliability that does not give out even if the application is subjected to situational extremes. This blogpost will help you in understanding the concept of electrical reliability.

What to expect from solder joints?

Solder joints are designed to last long. In sensitive applications like computers and surveillance systems, solder joints must outlast the life of the device in order to make sure the device keeps working until the last moment. The electrical reliability of a good solder joint enables:

• Good conductivity of current across the joint

• Homogeneity of the joint to offer less resistance to current flow

• Durability and endurance for long life and optimal performance

Joint reliability – tests performed to understand it

Solder joints need to perform on certain parameters if they are to be considered reliable. The thermal cycle test is performed on a solder joint to determine its reliability based on fatigue. In this test, a transition rate of 20°C per minute or less is applied to a solder joint to assess failure. When 63% failure has occurred in the solder joint, graphs are plotted to understand the patterns.

In moving applications of printed circuit boards, it is necessary that electrical conductivity of a joint be maintained with full integrity even if the board experiences vibration loads, which typically happens in automobiles, avionics and other transportation PCBs. Solder joints also need to have certain mechanical strength in order to save the connection in case the device experiences mechanical shock.

Electrical reliability of a solder joint determines how well current passes through the joint, which impacts the overall functioning of the device.

Ensure Smooth Solder Flow with Water Soluble Paste Flux

We all know how beautifully water flows. Now imagine, if this property was to come into the flux you use for all your soldering processes, wouldn’t that be nice? It would prove to be such a convenience in fluxing your board – things would become a lot easier. Today, in the soldering market, there are water soluble paste fluxes available which make the soldering process extremely convenient. In this blog, you will come to know why you should ensure smooth solder flow with water soluble paste flux.

Reason #1: Wetting properties

Water soluble paste flux is completely soluble in water. Since water has good wetting properties, it ensures that the flux dissolved in it comes in contact with even the most difficult areas on the printed circuit board. Good wetting property ensures good cleaning achieved during fluxing. This is the principal reason people prefer water soluble paste fluxes these days.

Reason #2: Easy cleaning

Water soluble paste flux provides easy cleaning of even the toughest of surfaces. Since water can reach practically any corner or niche of a printed circuit board, it makes for a highly effective medium to achieve quick cleaning which is meticulous as well.

Reason #3: Flowage

Flowage property of water makes the flux also equally flowy. This serves two purposes – it helps spread the flux evenly onto the surface of the printed circuit board, and when it is time to clean, it gets easily washed away with water as well. The flowage of water soluble paste fluxes makes them popular.

Soldering alloy mixed in with this form makes for an easy application of alloy onto the surfaces to be soldered together. You get a highly flowy liquid containing all the necessary elements required for good soldering. 

The Reliability and Solderability Factors of Lead-Free Soldering Bar

Soldering bars are bars of metal alloys used for soldering. Normally, for home soldering purposes, people prefer to purchase wires instead of bars. The reason is simple – domestic applications may not need as much alloy as a bar has to provide. Bars contain more metal, while a wire does not. In this sense, lead-free soldering bars are a convenient option for those who are looking at high volume soldering applications.

Lead-free soldering bars have this amazing convenience – they are available in weight ranges from anywhere from a few hundred grams to almost two kilograms. If there is a process which needs lead-free soldering alloy in high volumes, bars would be the best option. A wave soldering process, for example, requires molten solder alloy to work with – which automatically makes it a high solder volume procedure. If you are going to be undertaking wave soldering, purchasing lead-free soldering bars would be a good choice.

Lead-free soldering alloy bars are highly reliable as they have lower working temperatures. As compared to standard metal alloys used for soldering, lead-free soldering bars melt at relatively lower temperatures. There is lesser danger of burning the components while soldering them, which makes these bars highly reliable. This establishes a property of good solderability to lead-free soldering bars. Lead-free soldering bars also give a matte finish to the bond, which is highly desired for the cosmetics of the soldered joint.

Owing to such high environmental hazards that lead, as a metal, has displayed, lead-free soldering bars are becoming more and more popular as the safer and more environmentally responsible choice for soldering processes.

If you are still working with standard soldering alloys, switch to lead-free soldering bars today.

Choosing High-Performance Lead-Free Solder Pastes for Electronics Assembly

Environmental concerns have led the electronics industry to migrate from using leaded solders to lead-free solders. Various directives and regulations have been notified which make it mandatory for some electronics assemblies to be free of lead – which leads the industry enthusiasts looking for good lead-free high-performance solders. Here is a blogpost on choosing high-performance lead-free solder pastes for electronics assembly.

Lead-free solder paste alternatives are still in their burgeoning stages of development, which means there are certain errors or defects associated with them if not used mindfully. The first thing you need to consider is printability of the solder paste. Printability of a lead-free solder paste determines the magnitude of the defects arising at the end of the process – which is why it is important to get a solder paste with good printability. Printability factors such as recovery, printing speeds and durability need to be as high as possible.

The ratio of paste-to-metal in lead-free solders is another important factor to choose a high-performance solder paste. This ratio affects the cold slump of solder at drastic levels, which, if ignored, can lead to bridging defects in the finished product.

The lead-free solder paste can function optimally and form a good bond only if it has good wetting properties. The solder paste should be able to achieve maximum contact between components to be soldered. Cleaning should be easy – there should be no residue left behind upon examination. It would also work to your benefit if you perform a solder-balling test on the lead-free solder paste, just to be sure. Solder balls can be an extremely difficult defect to deal with.

Keep the above points in mind to choose a lead-free solder paste that is meant to perform during demanding situations for your printed circuit board assembly.

TIPS AND TRICKS TO USE LEAD (PB) FREE SOLDERING

The electronics manufacturing industry is changing, taking the world towards an eco-friendlier and sustainable future. The new initiatives of adopting lead-free solder in place of the conventional leaded alloys is a bold move, yes, but the sheer benefits it will generate for preserving the health and wellness of our natural environment definitely outweigh the challenges posed by this switch. By following certain tips and tricks, you can always make use of lead-free soldering alloys with your existing circuit board manufacturing tech and hardware to create good quality solder joints. Here are some points for you to follow:

Heat requirements

Whether your process involves hand soldering or machine soldering of components on your circuit board, the first and most important factor for you to take into consideration is the heat resistance threshold of all elements involved. You should make sure that your soldering iron, circuit substrate and electronic components – all can take increased heating temperatures (typically 70-110°F higher than leaded solder) necessary to make the lead-free solder a liquid. If not, the extended temperatures and longer dwell time might end up damaging these surfaces irreparably.

Suitable liquid soldering flux

Lead-free soldering necessitates that the flux used to clean, de-oxidize and decontaminate surfaces before carrying out the soldering process should also be capable of dealing with the higher temperatures involved. The flux shouldn’t burn or turn corrosive and damage the components on the circuit board. In most cases, liquid soldering flux with chloride compounds are considered to be most preferable and suitable for lead-free alloys.

Different aesthetics

Lead-free solder joints look substantially different from those created using leaded alloys. These joints will look duller and coarser as compared to their counterparts, but that doesn’t mean that they are lacking in strength, durability, resilience or performance matters. Take some time to understand its properties, both aesthetical and otherwise, before you decide to rework a joint.

Patience, patience, patience…

Lead-free solder behaves differently from its leaded alternative. It will take a longer time to achieve requisite flow consistency owing to its higher melting temperature. Its dwell time will also be significantly longer. Rushing the soldering process will only result in the creation of weak and unreliable joints with the alloy. Patience is the key here and you will need time to adjust your understanding of the soldering process in accordance with this new lead-free alloy. Take your time to understand before moving ahead.

HOW TO AVOID SOLDER BALLS AND BRIDGING DEFECTS DURING THE SMT REFLOW PROCESS

Solder balling and bridging are some of the most common defects that occur in the SMT assembly process carried out using solder reflow. In most cases, these issues are caused as a result of flaws in the PCB assembly operations or poor understanding of materials involved in the manufacturing process. This blog post explains some of the reasons for solder ball creation and bridging defects, and explores different corrective actions that can be taken to resolve these issues.

Solder Balls

Solder balls are usually created due to air or water vapor that may be left trapped in the solder paste. When this air/vapor escapes too quickly, it may take a small amount of liquid solder from the joint to create a ball like structure that violates the minimum electrical clearance principle.

Corrective Action for preventing solder balls:

•    Manage the solder reflow profile by increasing the pre-heating temperature of the PCB so that the flux evaporates properly before solder paste application.

•    Tweak the pad size for the PCB in accordance with your operational recommendations to prevent space that may trap air inside.

•    Manage solder flux application to prevent excessive amounts being plastered onto the board.

•    Bake the PCB before beginning the SMT printing and reflow process.

•    Ensure that the thickness of the copper plating holes on the PCB is greater than 25μm to prevent water from getting trapped inside.

Solder Bridging

Solder paste may form unwanted connections on the circuit surface if it flows abnormally and unexpectedly on the board. These connections usually connect adjacent surfaces, thereby making a conductive path which may eventually ruin the circuitry. This defect is known as solder bridging.

Corrective Action for preventing solder balls:

•    Add a solder mask between adjacent pads and surfaces to prevent abnormal flow of solder paste.

•    Tweak the design of the PCB stencil and change hole-aperture to better control solder paste application.

•    Avoid old and new flux being used together in a single application

•    Adjust the pressure of solder paste printing as well as the pick-and-place nozzle to prevent splashing.

•    Ensure there is a zero print gap between the PCB and the stencil.

Hope these inputs will help you in getting better results from your SMT reflow processes. If you are still experiencing solder balls or bridging defects in your PCBs, make sure you consult an expert for corrective action.

GOOD OR BAD: SOLDER BALLS ON A PCB

PCB manufacturing process follows a specific progression of steps that have to be executed perfectly in order to create reliable and electrically viable joints using solder paste. However, certain process flaws and inadvertent errors may lead towards creation of random small spherical particle-like shapes in or away from the main solder pool after the reflow process is complete. These spheres are known as solder balls. While some manufacturers may choose to ignore such an occurrence, the IPC A 610 standard deems a PCB with more than 5 solder balls (<=0.13mm) within 600mm^2 as defective. This is because solder balls that have a diameter of 0.13mm or within 0.13mm of traces can adversely impact the reliability of a PCB since they violate the minimum electrical clearance principle. So, the answer to the question of whether solder balls on a PCB are good or bad is clear – they are definitely bad.

Formation of solder balls in reflow or wave soldering operations is generally the result of uneven solder particle melt which may happen because of the presence of an oxide layer or improperly wetted surfaces. The creation of these balls can be random, non-random or may be to the result of a solder splash back. Trapped air or water vapor inside or below the surface of solder paste may try to escape when the circuit board is heated to get the paste to flow. When this happens, the air ends up creating a bubble like structure while taking some amount of solder paste from the surrounding surfaces. This spherical shape usually has a void inside where the solder paste hasn’t been able to reach. This occurrence can have an adverse effect on the reliability and functioning of the circuit board.

Considering these factors, it is important to analyze your PCB assembly process and find out the root cause behind the creation of solder balls. This analysis will help you determine the actual problem that needs to be corrected to prevent solder balls from forming. Consulting an expert organization like Alpha Assembly Solutions can help you in determining defect causes, from conveyor speed to surface contamination, and find cost effective ways to correct the same.

So don’t let solder balls hamper the quality of your PCB product. Go ahead and seek expert assistance to combat this issue today!