Properly soldering components onto printed circuit boards is crucial for assembling electronic devices. However, mastering PCB soldering requires skill and the right techniques to create reliable, high-quality solder joints. This guide explores tips and best practices to help develop expertise at hand soldering and achieve flawless results every time.
We’ll cover everything from understanding the PCB soldering process, to having the proper tools and workspace, to techniques for soldering various components. Additionally, we’ll discuss methods for inspection, troubleshooting common soldering problems, and steps to create robust solder joints that stand the test of time. Follow these tips to take your PCB soldering skills to the next level.
Overview of PCB Soldering Process
Before diving into tips, let’s quickly understand the PCB soldering process and what occurs when heat is applied to form solder joints:
- Rosin core solder wire contains flux and melts at around 380°F when heated
- The flux initiates solder wetting by removing oxide layers
- Solder alloy melts and adheres to the metal surfaces it contacts
- Heat dissipates away from the joint allowing solder to rapidly solidify
- The resulting joint forms both an electrical and mechanical bond
This basic process must be optimized through proper technique, tools, and work environment to achieve high reliability soldering.
Have The Right Soldering Equipment
Success begins with having quality soldering tools appropriate for PCB work. Investing in the right equipment prevents frustration and makes soldering far easier.
Soldering Iron Tips
Use a temperature controlled iron with interchangeable tips:
- Conical tips from 1/16” to 1/8” for general purpose use
- Fine point tips for precision soldering
- Chisel shaped tips quickly transfer heat to large pads
Well maintained tips prevent damaging PCBs and components.
For electronics use, 63/37 or 60/40 rosin core solder with 0.020” diameter works best. Match alloy to pad metallization.
Needle nose pliers, tweezers, flux brushes, and diagonal cutters handle delicate rework.
Solder Sucker and Wick
Essential for removing solder and fixing mistakes. Spring loaded suction bulbs work quickly.
Tip Cleaner and Stand
Conical brass wool and tip tinner keep tips shiny and wettable. A stand prevents tip damage.
Microscope or Magnifier
Inspecting solder joints under magnification ensures quality. Get at least 10x magnification.
The right tools enable successfully soldering even challenging connections.
Create an Efficient Workspace
Your soldering workspace greatly impacts efficiency, organization, and minimizing errors:
- Have good task lighting with no shadows on your work area
- Position the board securely in a vise or PCB holder at a comfortable angle
- Keep soldering iron safely in a holder when not actively soldering
- Organize tools, solder, flux, wick, etc. neatly within reach
- Use antistatic mats on working surfaces
- Sit comfortably at a desk or bench at the proper height
An organized workspace makes soldering relaxed and enjoyable rather than a chore.
Apply Proper Soldering Technique
Consistently creating quality solder joints requires proper technique. Follow these guidelines when hand soldering components:
- Use the minimum heat necessary to avoid PCB damage
- Ensure surfaces are clean and fluxed to facilitate wetting
- Heat pads and leads simultaneously before applying solder
- Allow a couple seconds of preheating to avoid cold joints
- Feed solder smoothly onto joint in a continuous motion
- Use just enough solder to fully coat the joint
- Keep soldering iron moving to avoid overheating
- Let each joint fully cool before moving the board
- Inspect all solder joints thoroughly under magnification
Proper technique comes with practice but prevents many issues up front.
Solder Components in the Right Order
For multilayer boards with mixed technology, follow this general sequence:
- Through-hole (THD) connectors first
- Other THD components from smallest to largest
- Fine pitch surface mount devices (SMDs)
- Other SMDs from smallest to largest
- Flat pack ICs last
This ensures heat absorption of larger components doesn’t impact small sensitive ones.
Apply the Right Amount of Solder
Judging how much solder to use takes practice. Follow these guidelines:
- THD joints should look slightly convex with a small fillet
- SMD pads only need enough solder to wet the termination
- Larger pads and ground planes need more solder volume for thermal transfer
- Avoid excessive solder that puddles, blobs, or produces bridges
Applying too little risks a cold joint. Too much causes bridges and difficulties cleaning up joints.
Solder Components at the Right Angle
Position the soldering iron tip so that the solder flows towards the tip and heated area. This allows:
- Better view of the joint while soldering
- Directs flux/vapor away from the work area
- Allows drawing the solder along as the iron moves
- Minimizes risk of solder splatter
Approaching joints at the proper angle gives more control and better wetting.
Tack Down Tricky Components
For ICs, connectors, or components needing precise alignment, first tack down one corner pin with a small amount of solder to hold it in place. This allows repositioning if needed before fully soldering remaining pins.
Use Both Hands When Possible
Using one hand to hold the PCB and the other to solder makes working easier. The board can be quickly reoriented as needed. This takes practice but improves precision tremendously.
Let Joints Cool Properly
Allow at least a few seconds after soldering for joints to fully cool and stabilize. Jostling or moving boards before joints harden can weaken or crack the connection.
Clean Flux Promptly
Clean any remaining flux residue immediately after finishing soldering each joint using alcohol, swabs, and brushes. This prevents oxidation or electrical leakage issues down the road.
Inspect Every Joint
Visually inspect each solder connection under magnification after cooling completely. Check for proper adhesion, fillet shape, discoloration, and pinholes. Reflow any faulty looking joints.
Troubleshooting Common Soldering Problems
Despite best efforts, problems can occur. Recognize and fix these common defects:
Cold Joint – Weak bonding from insufficient heat. Reheat joint fully and apply more solder.
Dry Joint – No solder adhered between surfaces. Flux and reheat fully before applying solder.
Bridge – Solder shorting between pads or pins. Wick away excess carefully.
Overheated Joint – Burnt flux, charred pads from excess heat. Allow area to cool before retrying.
Icicle – Conical solder shape from moving before cooling fully. Remain motionless as solder hardens.
Insufficient Wetting – Entire pad area not covered in solder. Reflow with added flux.
Catching defects early allows easy rework before problems occur in end products.
Some applications require moving beyond the basics:
Drag soldering involves depositing a trail of fresh solder along a row of pins as the iron slides along. This quickly tinning pins.
Similar to drag soldering but the iron is rolled along the joint to maintain optimal tip contact angle. Prevents bridging.
Pretinning Leads or Pads
Coating component leads and pads with a thin solder layer prior to soldering allows faster heat transfer and wetting.
Applying Solder to Iron Tip
Briefly apply a small amount of solder directly to the iron tip and allow it to melt onto the joint for faster soldering. Avoid excess.
Fume extractors remove harmful vapors and smoke during soldering. Important for health and avoiding chemical buildup on PCBs.
Working with molten metal and high temperatures warrants safety:
- Use eye protection against splatter
- Fasten loose hair and sleeves when soldering
- Handle hot irons with care – allow cooling before changing tips
- Keep flammables like alcohol away from work area
- Wash hands after handling solder, avoid touching face
- Ensure good ventilation to remove fumes
Making safety a priority prevents accidents and damage when soldering.
Mastering PCB soldering requires quality tools combined with proper techniques. Following these tips will help develop expertise at smoothly creating reliable solder joints. With practice, soldering components can become quick, rewarding, and enjoyable. Your perfectly soldered boards will function flawlessly for years to come.
Frequently Asked Questions
Q: What is the ideal soldering iron tip temperature for electronics PCB work?
A: Around 700°F (371°C) offers a good starting point. Adjust up or down depending on component size. Use lower heat for semiconductors or small SMDs.
Q: What diameter solder wire works best for soldering most PCB components?
A: 0.020” diameter 63/37 rosin core solder is a good general purpose size for hand soldering. For SMDs, 0.015” may be easier to manage.
Q: When soldering a pad, should the solder be applied to the pad or the iron tip?
A: Touching the solder to the pad generally gives superior results, allowing the heat to properly soak into the joint and achieve thorough wetting.
Q: What magnification is ideal for inspecting solder joints?
A: A stereo microscope or high quality magnifier around 10x power should suffice for clearly examining solder fillets, adhesion, and detecting bridges or cold joints.
Q: How can excess solder be removed safely from bridged or contaminated joints?
A: Solder wick or a vacuum solder sucker allow removing unwanted solder. Be careful not to lift pads or overheat components when desoldering.
3 PCB Soldering Tips During SMD Solder Process
PCB soldering is used for both through-hole printed circuit assemblies, and surface mount. In the latter case, the electronic components are glued by the placement equipment onto the printed circuit board surface before being run through the molten solder wave.
PCB Soldering services: Printed circuit board soldering that RayMing effectively functions to offer this services in China. Most of the buyers who wish to have quality soldering services with competitive prices can contact us for their requirements. We cater to majority of the specifications through our own PCB soldering plant in China.
Regardless, other electronic contract manufacturers, we possess own production facility in Shenzhen, China to offer effective soldering services as per your necessity. We have engaged experienced staff of 310 employees to undertake soldering of circuit board for different type of technologies.
We offer PCB lead free soldering process as per the necessity. We have employed experienced personnel and created two additional production lines specially for giving this service. We follow exceptional soldering processes in accordance to RoHS soldering prescribed guidelines and use modern techniques for quality inspection.
3 Tips Used for PCB Soldering :
1. The principle of soldering is to heat and melt the solid solder wire by a heated soldering iron, and then flow into the metal to be welded by the action of the flux, and form a firm solder joint after cooling. When the solder is tin-lead alloy and the soldering surface is copper, the solder first wets the soldering surface, and with the wetting phenomenon, the solder gradually diffuses toward the metal copper, forming an adhesion layer at the contact surface of the solder and the metal copper, so that the two Firmly combined.
2. The main functions of the flux are: removing oxides on the metal surface, removing impurities and dirt on the metal surface, and preventing the metal surface from being oxidized again. The role of solder resist is mainly used to prevent soldering between components.
3,A good solering point should meet the following standards: solder points into an inner arc; solder joints should be round, smooth and shiny. Clean no thorns, pinholes, voids, dirt, rosin stains. It should be ensured that the soldering is strong and no looseness.
Different Types of PCB Soldering Processes
When it comes to Printed Circuit Board (PCB) design and fabrication, soldering is of great importance. This is because, soldering is the process through which all components are placed on to board and if it is not of high quality, then PCB performance is also compromised. Soldering can be considered in a similar way to welding. This is process of bonding components on to board. Solder is basically an alloy which is placed among different components and modules over a board and are bonded together to achieve a specific purpose. Solder is being melted through a gun or soldering iron and when solder cools down it joins together copper track with components. There are various types of soldering depending on method and quality. This article is dealing with information related to soldering processes.
Soft PCB Soldering: The process of soft soldering is very popular and widely adopted in electrical and electronic industry. This method is creating an electrical connection among the components over circuit boards. The connection is also sometimes joined together through connectors or copper pipe. The solder used for this method is made of combination of tin with some other metals. For better bonding of the components on to the circuit board through soft soldering, an acidic substance known as flux is added for ensuring tight soldering connects. A gas or electric powered soldering iron is used for soft soldering process and the bond created as a result is often weaker than other types of soldering.
Hard Soldering: The hard soldering is known for the creation of a stronger bond than soft soldering as it incorporates use of higher temperature for melting of soldering materials. The soldering material used is usually silver or brass and blowtorch is utilized for melting purposes. The metal which is bonded as result is known as the base metal and is heated till a point in which silver or brass solder is melted for creation of stronger joints. Sometimes when soldering material used is silver, it is referred as silver soldering. Silver is much expensive when compared to brass even it melts at lower temperatures.
Brazing: Brazing is actually involving higher temperatures than that of both soft and hard soldering. The process of brazing is very similar to that of hard soldering process as the metal pieces or components are bonded with each other through heating. In this process by the time when you have heated the base metal, then the soldering material is placed on to it which is then known as the brazing filler metal among different surfaces. The material is instantly melting and the molten filler is joining components or base metals with help of capillary action.
The Reflow Soldering: The process of reflow soldering is one in which the soldering paste is heated. After heating now soldering paste is turned to molten state for connecting pins and pads of different electronic components with each other. The bond created through reflow soldering is permanent.
There are total of 4 steps in this process which are also known as zones. The zones are named as cooling, reflow, soaking, and preheating. All of the four zones are explained below in detail.
- The Preheating Zone: The preheating zone is usually referred to the increase in temperature from normal rang till 150-180 degree Celsius. The jump of temperature from normal to that of the 150 degree Celsius is in mere 5 degrees per second. Therefore, the total time required for going from a normal range to 150 degree Celsius is around 220 seconds or 3 and half minutes. The advantage of this slower warmup is that the solvent and water both are allowed to come out from the paste vapor in no time. This is also allowing the bigger components to be heated up constantly along with smaller components.
- The Soaking Zone: The soaking zone is ranging from the period of preheating from 150 degree Celsius to the time when alloy is molten. This means that the flux is getting active whereas the oxidized substitute is removed over the metallic surface and is ready for making a very good solder joint among pins of components and the printed circuit board pads.
- The Reflow Zone: The reflow zone is also known as the time above liquidus. The time above liquidus is abbreviated as TAL and is considered as the part of the process where highest ever temperature is reaching. A very common peak temperature adopted is in range of 20 to 40 degree Celsius above the liquidus state.
- The Cooling Zone: The temperature is slowly and gradually decreasing in the cooling zone till the time when solder becomes solid on the joints. It is to be noted that maximum tolerable cooling slope is required to be considered for avoiding defects to occur in the process. Therefore, a standard cooling rate of about 4 degree Celsius is recommended to be adopted.
Profiles for Reflow Process
There are two basic profiles which are involved in the reflow process i.e. the slumping type and soaking type. The soaking type is very alike to the trapezoidal in shape whereas the slumping type is similar to the delta shape. In case if the board is very simple and there is use of no intricate components e.g. BGAs or components of bigger size, then it will be best to choose the slumping profile else soaking profile is optimum to choose.
The following image is illustrating the difference of curves among the trapezoidal type and the delta type. It can be seen that trapezoidal type is having more curves while the delta type is growing in linear way till it reaches its maximum point and then drops down. Curve for both delta and trapezoidal is divided in to four parts. Part A is achieving 150 degree Celsius. Part B is till temperature elevates to 180 degree Celsius. Part C is when temperature goes beyond 230 degree Celsius and part D is when temperature drops down again from 230 degree Celsius. It is to be noted that peak temperatures for both types are same i.e. 230 degree Celsius.