Knocking Down the Bone Pile: Eliminating Solder Balls in Hand Soldering

Cause of the Problem
While solder balls can be produced during both SMT reflow and wave soldering, PCB hand soldering during touch-up or rework can result in solder ball formation. When moisture or other impurities entrapped in or on the surface of the PCB or component outgas during the hand soldering process, solder balls form. Baking out or cleaning the PCB or the component and comparing the results can help determine if this is the case. Soldering irons used to reflow solder paste during rework may also heat the paste too quickly and prevent the flux from fully activating, which causes the solder to oxidize and form solder balls.

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Solutions to the Problem
Solder balls form when the flux becomes molten and fails to clean all the soldering surfaces, which prevents the solder from coalescing into a single mass. The oxide coating that forms around smaller solder balls inhibits the solder from coming back together. Turning down the temperature of the soldering tip or using a lower tip temperature cartridge may solve the problem.

Because the soldering tip can only activate so much of the flux in each amount of time, slowing down the wire solder feed rate (Figure 2) or reducing the amount of solder being fed to create the solder joint (Figure 3) can also help prevent solder balls from forming. Fully activating the flux is the key to preventing oxide layers from forming.

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Utilizing a slightly more active flux that can withstand this temperature ramp is another option for preventing oxide layer formation. Using a hot air or IR reflow source with a slower defined ramp rate can eliminate the solder balling problem when using paste for rework. A slower ramp rate ensures that the flux is fully activated, thus preventing solder balls from forming.

Soldering techs need to be adequately trained in hand soldering and the variables affecting outcomes to reduce the chances of solder ball formation. Training should include adequately reinforcing the correct materials, choosing the correct tip as a heat bridge between the lead and the land, maintaining the correct tip temperature, and keeping the soldering tips clean. Inexperienced soldering technicians may feed in too much solder too quickly (See Figure 1).

Another area to consider when assessing the likelihood of solder contamination is component lead contamination. Potential sources of contamination include improper storage of the components, improper MSD controls of the component, and the cleanliness of the tape, tray, or stick the components are stored in.

With the proper solder training, or in some cases retraining, soldering technicians can pick up better habits and help diagnose problems as they happen.

Reminder of the IPC-A-610 Spec on Solder Balls
A refresher is in order on what the inspection standard says about solder balls. Solder balls (IPC-A-610H 5.2.7.1) become a defect when:

  1. The presence of a solder ball reduces the distance between the solder ball and another conductive surface to below the minimum electric clearance.
  2. The solder ball is not entrapped, encapsulated, or attached, or can become dislodged in the service environment. A solder ball rolling around in an electronics enclosure is not acceptable.
  3. The solder ball is entrapped in coating or flux residue such that other form, fit, or functions of the electronics assembly cannot be maintained.

Removing Solder Balls
Solder balls can be removed by several means. For solder balls entrapped in flux residue, an orangewood or plastic stick can dislodge the solder balls. The challenge is making sure that solder balls dislodged in this manner do not get "lost" in the assembly and create a future reliability issue. Large solder balls can be removed with a soldering iron, flux, and soldering braid. If entrapped by a conformal coating or other material layer, the coating will need to be removed prior to eliminating the solder balls.

While solder balls typically appear in other PCB assembly processes, those formed in hand soldering can be mitigated through a variety of methods including proper flux usage; proper soldering tip and temperature selection; and by keeping the materials in the soldering process free from moisture and contaminants.

This column originally appeared in the December 2022 issue of SMT007 Magazine.

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2022

Knocking Down the Bone Pile: Eliminating Solder Balls in Hand Soldering

12-07-2022

While solder balls can be produced during both SMT reflow and wave soldering, PCB hand soldering during touch up or rework can also result in solder ball formation. When moisture or other impurities entrapped in or on the surface of the PCB or component outgas during the hand soldering process, solder balls form. Baking out or cleaning the PCB or the component and comparing the results can help determine if this is the case. Soldering irons used to reflow solder paste during rework may also heat the paste too quickly and prevent the flux from fully activating, which causes the solder to oxidize and form solder balls.

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Knocking Down the Bone Pile: Opening a Trace on the Surface of a PCB

09-28-2022

Because of PCB layout problems or required circuit modifications, at times a trace on the surface of a PCB needs to be severed. In this procedure a small section of the trace is removed, thereby forming a “break” in the circuit. In general practice, the length of this trace cut is as least as wide as the minimum conductor spacing. In most cases, a very sharp-edged knife or high-speed mill will make the cut. After cutting the areas is tested and then sealed with epoxy.

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Knocking Down the Bone Pile: Soldering for QFPs and Other Gull Wing Leaded Parts

08-16-2022

There are multiple methods for hand soldering QFPs as outlined in the IPC 7711.21 Rework and Repair of Printed Circuit Assemblies process guidelines document. QFPs have several challenges related to their hand soldering especially when the component has a high lead count. While these are a head-spinning number of techniques, this discussion will concentrate on some of the more widely used techniques: drag, and point-to-point soldering as well as the adhesive-backed stencil technique.

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Knocking Down the Bone Pile: Reworking of SMT Connectors with Center Ground Connection

05-18-2022

Connectors such as those pictured in Figure 1 are challenging to rework as they generally have a high density, tight spacing of connector pins as well as a ground connection running through the center of the body of the part. The generic term for these types of connectors are surface mount center ground connectors. These surface mount connectors are designed for parallel board-to-board, flex-to-board, and cable-to-board configurations, and are generally compatible with both infrared and forced air convection rework heating methods. Specifically, a popular type of this connector configuration is a mezzanine connector which connects two parallel printed circuit boards in a stacking configuration.

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Knocking Down the Bone Pile: Solder Mask Repair Techniques for PCB Repair

03-08-2022

One of the most common physical repairs (restoring functional capability of a defective PCB while not complying to meet original specifications) on a PCB is the repair of solder mask. Solder masks’ purpose is to prevent solder from flowing from one point to another during the original assembly process. Damage to solder mask can be aesthetic or functional in nature such as the case when the mask preventing solder from flowing down the “dog bone” of a BGA causes the BGA ball solder joint to be “starved” thereby causing a defect.

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Knocking Down the Bone Pile: Humidification for ESD Control in PCB Rework/Repair

01-05-2022

The amount of charge generated in an electronics rework and repair area is affected by a variety of factors including but not limited to the materials used, the amount of frictional interaction between materials as well as the relative humidity of the environment. During the cold winter months in northern climates when the heating systems dry out the plant air and the relative humidity falls, higher electrostatic charges develop all other things being equal. Lower humidity can increase the number of ESD events so theoretically it stands to reasons that keeping the rework area at higher humidity levels will reduce the chances for charged-induced damage to components.

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2021

Knocking Down the Bone Pile: Methods for Underfilled Component Rework

11-17-2021

Products such as engine control modules, drones, smartphones, and other handheld communication devices, which are designed for high reliability and require high processing power, often have a BGA or CSP package as the processor. Underfill has been a solution at the package level protecting these devices from the coefficient of thermal expansion (CTE) mismatch between the device and PCB or between the die and the component substrate for flip chip packages. Stress caused by CTE mismatch redistributes the stress from the bottom of the solder spheres to the entire component.

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Knocking Down the Bone Pile: X-ray Imaging and BGA Rework

09-08-2021

X-ray imaging prior to the removal of a BGA for rework will help the rework technician point out potential issues which may be challenges to successfully removing and replacing the BGA.

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Knocking Down the Bone Pile: Cleaning of ‘No Clean’ Fluxes in PCB Rework

07-26-2021

The original intention of a “no clean” solder was to eliminate the post PCB assembly cleaning process while still not risking any performance or long-term reliability degradation. Some industry surveys indicate that about one-half of assemblers using no clean flux chemistries clean the PCB after assembly.

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Knocking Down the Bone Pile: Solder Excavation and Rework

05-10-2021

In order to properly perform rework—the removal and replacement of a component on a PCB—the remnant solder needs to be properly removed after the component has been desoldered and removed. Bob Wettermann breaks down the methods.

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Knocking Down the Bone Pile: Salvaging Components for Other Uses

03-04-2021

Electronic components and their availability (or rather their lack of) have been in the news recently. Automotive suppliers are struggling with their supply chain as electric vehicle production, and the associated consumption of electronic components continues to expand.

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Knocking Down the Bonepile: Fixing Vertical Hole Fill in Plated Holes

01-10-2021

For PCBs with larger thermal mass—such as found in high layer count boards or boards with higher weight copper layers—proper and consistent hole fill can be a challenge. It is critical to make sure that these non-visible defects do not become quality escapes while also making sure the proper rework techniques are applied; to get these plated holes properly filled is important.

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2020

Knocking Down the Bone Pile: 5 Habits to Make Your Soldering Iron Tips Last Longer

11-02-2020

Poorly maintained soldering iron tips have real costs associated with their lack of care. To maintain the integrity of the soldering joints and prevent the tips from becoming a runaway consumable expense, Bob Wettermann shares several areas of tip care that can prolong their life.

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Knocking Down the Bone Pile: PCB Rework of 0201 Packages

09-07-2020

As electronic passive components continue to shrink in size, methods for their rework need to be developed by electronic manufacturers to maintain and support PCB assembly processes. Bob Wettermann compares and outlines a few of these rework methods.

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Knocking Down the Bone Pile: Removing Conformal Coatings for PCB Rework

07-27-2020

When the removal and replacement of components due to field failures or manufacturing defects needs to occur, the overlaying conformal coating layer first must be removed before being able to remove and replace a component. Bob Wettermann explains.

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Knocking Down the Bone Pile: Getting to the Root Cause of BGA Assembly Problems

05-04-2020

When potential process defects begin showing up underneath BGAs in electronic assemblies, there are numerous failure analysis tests that can be used to troubleshoot process problems. These investigative methods begin with non-destructive test methods and progress to destructive methods as some of the possible root causes are eliminated.

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Knocking Down the Bone Pile: Underfill Rework and Solder ‘Squirt Out’

01-02-2020

One of the toughest rework challenges is removing and replacing components on PCBs with underfilled components. Many times, underfill is used to provide a shock barrier to component solder joints of handheld electronics, such as notebooks, tablets, and phones. This underfill is added post-test in the assembly process and is dispensed underneath components, such as BGAs, QFNs, and LGAs.

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2019

Knocking Down the Bone Pile: Electronics Assembly Industry Outlook

12-17-2019

Geographically, our products go directly into the market around the world, our rework and repair services are a harbinger of the EMS build market, and our training services are hyper-focused in the Midwest of the United States. Therefore, we see much of the activity in the global electronics supply chain. There are numerous PCB rework/repair challenges being faced by North American customers. One trend has to do with increasing package sizes, which are being driven by the market desires. In the past five years alone, the state-of-the-art semiconductor package has gone from approximately 10 to 30 billion transistors on a single package.

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Knocking Down the Bone Pile: Process Methods for Reworking High Lead Count SMT Parts

10-09-2019

There are numerous methods for getting the solder onto the right pads in the right volume during SMT rework of high pin count or very small footprint SMT devices. The most common types of solder deposition include printing, dispensing, and hand soldering. Each of these methods has pros and cons, depending on a variety of factors in the rework process.

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Knocking Down the Bone Pile: BGA and PCB Warpage—What to Do

07-10-2019

Warpage of BGA packages or PCBs can occur when any heating and subsequent cooling cycle is gone through. This may leave the package to bow in the middle. Pushing the corners up or downward will show up in bridging (caught on X-ray) or cause opens that would show up on endoscopic or visual inspection. Here's what you need to do.

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Knocking Down the Bone Pile: Straightening Out Those Corners

05-22-2019

A PCB can be dropped, dinged, or mishandled as it is placed into a board carrier in the PCB assembly operations area. When the laminated material is damaged in this manner, can it be repaired? The answer, like most engineering answers, is that it depends. Read on.

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Inspection of BGAs After Rework

03-21-2019

After removing and replacing a ball grid array (BGA), the acceptability of the interconnection of the solder balls to the PCB should be assured, because this assurance and the criteria for that assurance are the customer’s outgoing inspection criteria.

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How Much is Too Much?

01-09-2019

One of the typical questions process engineers pose regarding the PCB rework process is, "How many heat cycles are too much?" Asked in another way, the question is, "How would one define a limit on the number of times a PCB can be reworked while still being reasonably assured that the reliability has not been impacted based on its operational environment?" Find out how.

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2018

Proper Thermal Shielding Yields Highest Rework Results

11-21-2018

There are numerous "gotchas" if the rework technician does not care for components and materials neighboring the component rework area. However, careful planning, shielding, and sometimes removing a neighboring device or material will ensure the highest possible rework yield.

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Filling the Gap: Underfill Rework

09-21-2018

Rework technicians must take into account a variety of factors when considering whether or not to rework underfilled components, such as BGAs, CSPs, flip chips, and other component packages on handheld devices. But without a full understanding of the underfill characteristics, expect the outcome to be low yields unless the board was designed with reworkability in mind.

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Replating of Gold Fingers: Getting the Shine Back

07-30-2018

There are several instances where the gold contacts on PCBs need to be replated, and IPC A-610 discusses several of these cases. This column by Bob Wettermann discusses gold replating of defective contacts caused by processes such as wave or selective soldering, or plating.

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Masking of Conformal Coating During Assembly and Rework

06-11-2018

Masking of printed circuit boards post rework/repair as well as for initial PCB assembly is often required if the PCB is to be conformal coated. If a board that has conformal coating on it needs to be reworked or repaired, the conformal coating needs to first be removed before the operation of rework or repair can take place. This article centers around the various options for conformal coating masking via a liquid application process.

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Device 'Dead Bugging'

04-20-2018

"Dead bug" attachment of electronic components is a way of building functioning electronic circuits by soldering the parts directly together or by soldering miniature jumper wires between the component leads and the PCB lands instead of the traditional surface mount or through-hole soldering of components onto a PCB.

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PCB Pad Repair Techniques

01-08-2018

There are a variety of reasons behind pads getting "lifted" completely or partially from the laminate of a PCB. Per the just revised IPC-A-610 Revision G, a defect for all three classes occurs when the land is lifted up one or more pad thicknesses. Lifted pads can occur when a device has been improperly removed or there is a manufacturing defect in the board construction. In any case, as with any repair, the ultimate decision on the ability to repair the pad lies with the customer.

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