How to Test Solder Joints with A Multimeter

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Have you ever experienced solder joint problems in the past? How did you take care of the concern? Did you get the help you need? If not noticed instantly, a solder connection on your circuit board could become a huge disaster. 

After you have finished a solder joint, you must check it to ensure the joint is good. Inspect it closely and look at it under a magnifying glass. Slowly wiggle the component to determine if the joint is stable or not. 

Keep in mind that a good solder joint must be shiny and full but does not overflow the pad. 

Soldering is a procedure that enables you to fuse or attach two metal pieces together through heat, a hot iron, and a metal alloy filled made of tin and lead, also referred to as solder. This method is widely utilized in electronics and engineering professionals for the making and repairs of products.

Nevertheless, this work productivity and the process could be severely obstructed if you find that your solder won’t stick and result in bad solder joints. 

All bad solder joints are commonly caused by one of three things:

  • melting the solder with the soldering iron instead of with the wire lead
  • applying too much solder
  • not letting the pad and wire heat sufficiently 

Reasons Why Your Solder Joint is Not Working as You Planned It to Be 

Bad solder joints can take place for many different reasons. Sometimes, the cause lies in the fact that the thickness and design of the stencil used in SMD (surface-mount technology) reflow determine the amount of solder paste deposited on the PCB (printed circuit board). 

Nothing is more stressful in the soldering process than to melt solder over your project and find that it is not sticking or fusing. 

Before you successfully try again, here are some of the typical indications of why a bad solder joint happens: 

  • The solder runoffs the pad, and it touches an adjacent pad

This situation can occur if you apply too much and if the pad did not get hot enough to accept the solder. That occurrence can cause your solder to flow off the pad and into the adjacent pad. 

Do you notice the solder spilling over from one pad to the adjacent pad? Then it’s a clear indication your circuit is not right. 

  • The solder itself is not shiny 

Did you know that shiny solder often means the solder is heated, flowed, and cooled appropriately? The solder will be dull when it cools, especially if it gets barely hot enough and flows over a paid or wire, which is not sufficiently heated. 

Unluckily, the new lead-free solder nearly always cools fully. Therefore, it often looks like a bad solder joint when the joint is not that good. 

  • The solder is not inflexibly connected to the pad, or the lead is loose in the hole

One clear reason for this is because you transferred the lead before the solder had totally cooled down. 

  • The lead and pad are not 100% covered with solder. That allows you to see through the hole’s one side through which the lead passes 

This happens because you did not apply enough solder, or the pad was not hot enough to accept the solder. 

Solder joint test that uses a multimeter is the best and often the only way to locate faulty joints. 

Should You Test Your Solder Joint? 

It is crucial to check your PCB assembly supplier to learn the technology included in their welding and solder joint tests. If your supplier does not invest in a sophisticated tool or only depends on manual inspection like a bare eyes test, you could be on a rocky ride. 

When the PCB is not inspected properly, short connections and bad solder joints might go undetected, causing serious challenges in the final product. Sometimes, those issues become obvious during QA testing. Worse, short joints may lead to burning out an IC (integrated circuit) or two. 

So, How Do You Test Solder Joints through a Multimeter? 

A multimeter offers many different ways of measuring different things. One of the things it can measure is voltage and DC circuit. It can also measure AC voltage, the amount of current flowing through a circuit, and do some work on transistors.

  1. To use a multimeter in your solder joint, begin by setting the dial to the next value up from the value you are expected to see. Connect the probes: the black goes to the COM while the red probe goes to the VΩHz. 
  1. Grab your probe and put it on the end of your resistor. It doesn’t matter which the red goes. Just make sure it’s touching one resistor and hold it there. Put the black probe on the other resistor. You will then get a reading. 
  1. Try to touch the multimeter’s positive lead to some parts of the wire ahead of your solder joint. Touch the negative lead to the end of the connector port on the other side of the solder joint. 

At this point, the meter must read zero. Do you see any sort of resistance? Then that indicates a bad solder joint. 

  1. The good thing about testing with a multimeter is that you can always use the continuity function. All you have to do is to set the continuity mode on your device, then touch the leads together and ensure there’s a beep on the multimeter.

Touch the leads to two points on your solder joint’s opposite sides. Your device will make a beep sound when there’s a detected continuity. That also suggests that conductive material connects the points between the leads, not to mention the solder joint is great from a continuity perspective. 

Meanwhile, if you don’t hear your multimeter beep, then you don’t have continuity. 

To sum up, using a multimeter to test solder joints can certainly help avoid bad solder joint issues before they actually happen. We hope you find this article informative and helpful. 

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