How to Surface Mount Solder: Critical Steps in Surface Mount Technology

Every electronic circuit board you interact with features hole components and surface mount devices. 

But do you know how to surface mount solder components? 

Also, is there a unique way to create strong solder joints without solder bridges in surface mount technology? 

Join us as we look at the specifics of surface mount technology and the primary solder processes involved in installing parts. 

We’ll discuss everything in detail, leaving all your questions answered. 

Types of SMD Soldering Process

There are two main traditional soldering methods for SMDs. 

The primary reflow soldering process that has been in use for an extensive time is IR soldering

So why has it stood the test of time?

  • Primarily, the yield from infrared soldering is remarkably high. 
  • Also, infrared soldering is among the best low-cost individual soldering processes with good results. 

The other popular reflow soldering process is Vapor phase soldering

While it is less popular than convection soldering (IR soldering), it applies to special soldering applications. 

Other common surface mount soldering techniques include hot bar resistance and laser soldering

When deciding on the ideal soldering method, your primary consideration should be your intended outcome and the materials. 

Also, the perfect method should have the most minor solder defects. 

SMD Soldering Process for Mass Production

Numerous PCBs. 

Numerous PCBs. 

Applying the typical soldering techniques in an industrial setting is uneconomical as it would waste a lot of time. 

Therefore, soldering is mechanized, and manufacturers use special SMT machines such as reflow ovens. 

It helps boost the overall throughput, and there are very few to no cold solder joints because the technology is perfect for delivering solder particles to the joints. 

Manual SMD Soldering Process

Soldering Iron. 

Soldering Iron. 

The alternative to the above option is to go the manual way, using conventional soldering techniques.

 It means that before getting started, you will need to have the following in place: 

  • Solder Wire
  • Soldering station/soldering iron
  • Solder paste
  • Hot Air SMD Rework Station
  • Solder Flux

Due to the necessary manual input and the lack of mechanization, this technique best suits repair works. 

Also, it makes sense to use it for individual rework processes. 

Selection of Soldering Process

An engineer soldering parts in the workshop. 

An engineer is soldering parts in the workshop. 

Despite the convenience of the surface mount technology, we are yet to entirely phase out the application of through-hole technology. 

Why? Because using surface mount soldering in tandem with the hole counterpart is complementary. 

Therefore, the choice of the ideal soldering method depends on the components we’re looking to solder.

 Hence, we won’t advise you to pick on one specific technique, as all methods matter in various scenarios. 

Advantages and Disadvantages of Surface Mount Soldering

Industrial Surface Mount of PCB components. 

Benefits of Surface Mount Soldering 

  • The use of automated machines to pick and place the SMT components, this technology makes it easy to create closely packed circuit boards. This close-packing of adjacent components is critical in creating small form factor devices. 
  • Also, it is possible to identify the correct component location even at high-density packing while ensuring significantly low resistance and inductance at the joints. 
  • The technique results in significantly lower emitted radiations primarily because there’s a relatively smaller radiation loop area. 
  • Moreover, you can use small components with this method, as the packing is not an issue. This factor is critical in lowering the cost of the materials, which is imperative, especially in industrial production. 
  • For mass production, a surface mount solder station is arguably the fastest and most straightforward technique for industrial PCB assembly. It can produce up to 2000 parts in one minute, making it excellent in realizing production throughput requirements. 
  • Finally, it results in small mass devices, which means a lot, especially if you want to create portable units such as pocket-size phones. 

Disadvantages of Surface Mount Soldering

  • It’s not the ideal method to create strong joints, especially for devices in demanding conditions such as military work. 
  • Also, the technique’s success primarily relies on the solder paste’s surface tension to create a strong bond at the joint. Therefore, while it’s best for miniature components, it’s not a preferable technique for large electronic parts. 
  • Again the high throughput rate of the method is a significant problem because it can lead to defects, solder bridges and weak joints. 

How To Surface Mount Solder

Manual Soldering. 

Manual Soldering. 

Let’s explore the solder mounting components procedure for a simple PCB assembly process. 

We’ll guide you on achieving a 0.5mm spacing between the individual component pins. 

Parts and Components

  • Various SMD (Surface Mount Device) components should ideally fit on the custom PCB you’re using. 
  • An antistatic cloth
  • Soldering Iron
  • Water Soluble Solder
  • Rosin Flux. You can still use liquid flux if the other is not available. 
  • Water/ Rubbing Alcohol
  • PCB for assembly. 
  • Desoldering braid
  • A pair of tweezers

Prepare the PCB

The most crucial aspect is ensuring your PCB solder pads align with the SMD pins. 

Again ensure that the PCB is clean because dust will hinder bond formation. 

So wipe it off with the antistatic cloth gently. 

Also, at this stage, it’s essential to set up the soldering iron at the right temperature, at approximately 600 degrees. 

Take caution during this process, as at high temperatures, you risk getting a burn if you touch the hot iron. 

Position the Components

Set up the components on the circuit board, ensuring that you place the pins at their positions on the solder pads. 

After setting it up, tack in one pin at the corner pad. Make sure you’re firmly holding the pin in position using your tweezers. 

Once you place the pins, bring the hot solder iron onto the PCB and gently heat up the pad to melt the solder and form a bond. 

Apply Flux

You will need to apply flux, preferably using a brush to avoid messing your clothes. 

Ideally, place it on the opposite side of the component pin you’ve just soldered. 

The essence of the flux here is to hinder solder beading and improve the solder flow process.

Solder 

Soldering process. 

Soldering process. 

Now it’s time to apply the soldering wire to form a permanent bond. So place a wire adjacent to the component pin. 

Next, place the soldering iron on the opposite side to melt the wire. The solder will evenly flow around the area, forming an excellent bond. 

Remove Soldering Bridge

Desoldering Braid. 

Desoldering Braid. 

The desoldering wick we listed on the components list is for use in this step.

 It is essential because solder bridges are inevitable in any soldering process. 

And solder bridges can significantly affect the performance of your circuit board, so you have to fix it. 

Here’s how to desolder: 

  • First, lay the desoldering wick on top of the excess solder. Next, place the hot soldering iron on top of the wick to heat it up. It will, in turn, melt the solder underneath. Gently pull the desoldering wick, and it’ll peel off the solder. 
  • The critical bit when desoldering is to ensure you are careful not to destroy the solder parts. So be gentle when removing the wick; if the solder proves challenging to remove, consider adding more heat to the wick. 

Also, remove the extra solder in the other parts. 

Clean With Rubbing Alcohol or Water

This process will depend on the solder type you used above. For water-soluble solder, alcohol is not necessary. 

In this case, simply wipe the soldered part with the antistatic cloth dabbed with water. 

Concentrate on the parts with extra flux to ensure you remove it all. 

Summary

You need the expertise to apply even the tiniest bit of solder on a PCB because if you get the process wrong, you’ll mess up the PCB assembly process. 

Luckily, in an industrial setting, automatic systems handle this process. This guide will come in handy for your DIY soldering of surface mount components. 

The steps are straightforward; if you follow each step, you can form a strong joint. Also, we’ve equipped you with the know-how to deal with excess solder.