10 Issues We Need to Pay Attention to in PCB Soldering

When it comes to PCB soldering printed circuit board components, hand soldering has been considered an iconic skill owned by the manufacturer for long. If you are manufacturing high-level PCBs, for instance, then there are high chances that you'll be soldering using specialized machines.

Anybody can try his/her hand to solder components on a printed circuit board. But with such parts becoming more compact and smaller by the day, the chances of encountering issues to do with soldering seem to have increased significantly.

But regardless of whether there's the involvement of machinery or hand soldering, errors are prone to occur. This article points out the top ten PCB soldering issues to note.

(Be keen on possible solder issues with your PCB，Problems in PCB soldering)

1.Tombstone (Lifted Components)

If you have a marker or lifted components on your printed circuit board, it means that these components are higher than the PCB. Such mainly take place during the process of wave soldering, ending up resembling a tombstone.

• Lifted components is a common printed circuit board issue that a lot of PCB manufacturers face. Some of the most basic causes of lifted parts include the following:
• Using components that consist of varied lead or thermal solderability requirements.
• Wave is PCB soldering flexible PCBs that tend to bend as the components remain flat.
• An incorrect length of lead that happens to lift as it enters the solder bath.

（PCB soldering process Lifted components on a damaged PCB)

2.PCB Soldering Solder Bridging

When PCB soldering components on a printed circuit board, you may encounter cases of solder bridging. Solder bridging takes place the moment two solder joints connect. When the two solder joints connect, they form an undesired connection that might eventually lead to short circuits on the board.

When two or more pins bridge together, you'll encounter trouble with your boards. Some of the significant causes of solder bridging include the following:

• We can not fail to orient the same types of components in the same direction.
• We can not fail to leave enough space between the pads and the solder mask layer.
• Designing and manufacturing printed circuit boards without paying attention to weight distribution. Such happens, especially when small components all sit on one side of the board.

(PCB soldering A pic of a diode bridge)

3.PCB Soldering Excess Solder

Excess PCB solder on printed circuit boards is a big challenge that manufacturers face when producing these boards. If a board PCB passes through a wave soldering machine but takes too much solder, they'll be an excess solder build-up. Excess solder on a printed circuit board will eventually have an impact on its functionality.

Just like Lifted Components and Solder Bridging, there several major causes of excessive solder. Some of them include the following:

• We can not use Failure to orient the same type components in the same direction during wave soldering.
• Employing the use of incorrect lengths to pad ratio when designing the printed circuit board.
• Conveyor belt running fast on the manufacturer's side.
• For you to avoid cases of too much solder, it's advisable not to get too enthusiastic to the extent of applying a lot of solder on the pins.

(A PCB damaged due to excess PCB soldering)

4.PCB Soldering Solder Balling

Solder balls also come in as common soldering issues worth noting. Solder balls appear as small spheres of solder that adhere themselves to the conductor surface or the laminates. Solder balls typically take place either during reflow or wave soldering.

Several causes may bring about solder balling. The most common ones include:

• Solder peeling, falling back, and splashing onto the board during the process of wave soldering.
• We did not use solder paste printing correctly.
• The use of already oxidized electronic components.
• Incorrect reflow temperature settings.
• The soldering temperature in wave soldering machine or equipment is high.
• Solder liquid spitting back onto the board upon heating the flux.

(PCB Solder balls on a PCB)

5.PCB Soldering Cold Joints

On a printed circuit board, cold joints appear somewhat pock-marked, lumpy, and dull. But what is a cold connection? In short, a cold junction takes place when the solder doesn't melt completely, resulting in a lumpy or rough surface. Cold joints are highly unreliable, and a common printed circuit board soldering issue facing plenty of manufacturers.

Cold joints occur due to some reasons worth noting. Primary reasons for cold joints are:

• The soldering iron or the solder joint itself is not heated enough until it is needed.
• Ground the pad directly without considering heat dissipation.
• Accumulation of flux under the circuit board causes the solder to adhere incorrectly to the connector.
• Use uneven SMD components in the design process.
• Use an inappropriate wave height between the circuit board and the solder wave.

(cold joints on a PCB)

6. PCB Soldering Overheated Joints

Similarly, too little heat brings about wonky connections; a lot of heat also leads to a splitting headache on your end. With overheated connections, your printed circuit boards will not play the role that you would intend. However, burn flux resulting from overheated connections can be removed by carefully scraping a toothbrush or isopropyl alcohol.

Some of the causes of overheated joints are:

• Setting high temperatures to the soldering iron.
• Solder failing to flow as desired.
• We can not fail to clean dirty looking pads and joints.

To further avoid overheated joints instances, then it's advisable to use a clean, and hot PCB is soldering iron. Additionally, the ideal preparation and cleaning of the joint help prevent instances of overheated joints.

(Overheated PCB joints)

7.Solder Skips

Just as the name suggests, solder skips occur when solder get to skip over some surface mount pads. Solder skips are undesirable as they leave unconnected pads or areas. Solder skips are more of unsoldered surface mount joints on a printed circuit board.

Causes of unsoldered surfaces or solder skips can include aspects such as:

• A manufacturer using incorrect wave heights between the board and the soldering wave.
• Using uneven pad sizes for Surface Mount Devices (SMD) during a manufacturer's design process.
• Gassing of flux beneath a printed circuit board, causing the solder to adhere to the board improperly.
• Having excess resist thickness.
• Contaminated flux.
• Blocked nozzles or uneven foamers during the wave soldering process.
• Flux getting blown off.

8.PCB Soldering Solder flags

On their own, solder flags are ideal as they ensure that a printed circuit board enjoys proper connection. However, solder flags or spikes may be indicators of insufficient or incorrect flux application. Such may end up "flagging" or bringing about solder issues in other places of the board.

Solder flags are common PCB issues whose major causes include:

• Inconsistent application of flux.
• Improper control of solder drainage coming from the wave.
• The oxidation of printed circuit board components due to poor storage and transportation.
• Inconsistent lead lengths that may exceed the recommended 2.00 mm.
• The occurrence of shorts.

9.PCB Soldering Solder Discoloration

While this printed circuit board issue may appear somewhat cosmetic, nevertheless, it's still worth noting. Solder discoloration is frustrating, and your manufacturer needs to take some time to discover its root causes. A solder resists on the printed circuit board, or a conveyor belt may find a mask discoloration.

Some of the most well-known causes of solder discoloration include:

• PCB manufacturer chooses to use different flux materials or high temperature during soldering.
• PCB manufacturers choose to use different flux materials or high temperature during soldering.
• PCB Manufacturers are mixing batches of the circuit board in the same process of wave soldering.
• Longer dwell times.
• Changing a printed circuit board supplier.
• We need to run the printed circuit board more than twice in a tray.

Luckily enough, you can do away with instances of solder discoloration. Among other things, you need to partner with a company with significant and working quality assurance protocols.

10.Blow Holes and Pin Holes

Pinholes and blowholes are easy to identify on a printed circuit board. All you have to do is to look for any holes in the solder joints. In most cases, these holes extend from the layer that you are observing to the internal layers. Also, they may extend to the bottom of the board, bringing about connectivity issues.

The main causes of blow and pins can include:

• Excess moisture that builds upon the circuit board.
• The components cannot be oriented in the same direction during welding.
•  In the design stage, the via ratio is too small or too large.

(Blowholes and pinholes in a PCB)

Summary

So there you have it, some of the top 10 soldering issues that may bring damaging effects to an excellent PCB design. But you need to remember that if you encounter any of the above problems, they aren't necessary due to your fault.

If you want to ensure that you do away or significantly minimize PCB soldering issues, we at OurPCB have a few recommendations. Ensure that you follow the required PCB soldering steps in addition to keeping a DFM checklist on hand.

If you find hand-soldering somewhat tasking on your end, then feel free to contact us. We can easily source all your components and subsequently assemble them a full board for you. With more than a decade of experience in PCB soldering, you can trust us to deliver. Call us today, and let us handle your printed circuit board soldering challenges as you sit and relax.