Knocking Down the Bone Pile: 2023’s Top Challenges in BGA Rework

Over seven years ago, I put pen to paper to enumerate the top challenges needing to be overcome for a successful BGA rework. With the continued advancement of BGA technology, it’s time to apply a fresh coat of paint to that list. Read on to find out my revised take on today’s top BGA rework challenges (in no particular order).

Challenge #1: Very Large BGAs
As devices become more complex and computing power requirements increase, the maximum physical size of BGA packages has continued to increase. Currently, some devices in development are planned to be 125 mm x 125 mm in size. These large package sizes present some very challenging scenarios for rework process technicians.

Today, the placement systems for such large packages are limited by the split vision prism systems that align the components during placement. To successfully handle such large packages, BGA rework equipment vision systems will need to be upgraded.

Bottom heaters, which ensure that the board onto which the package is placed is uniformly heated, need to be upgraded to handle these large component package sizes. Undersized underside heating sources may cause an inconsistent temperature gradient from the top of the component to the underlying area, thereby sending different areas of the component into reflow at different times. This results in component balls that are stretched or elongated; “cold peels” due to improper temperature profiles can also damage BGA pads on the board.

Maintaining a consistent temperature over the entire component surface area presents another challenge in reworking these large packages. Air flow turbulence in the hot air rework nozzles can make it difficult to maintain a consistent reflow temperature coming out of the nozzle, which limits its ability to uniformly reflow and remove these large packages. Similarly, many commercially available IR rework systems do not have a spot size which can cover the entire size of these packages heat the component uniformly.

Custom-machined board supports for these larger packages, stay-in-place stencils to open the process window through solder paste printing, and a thorough understanding of proper thermal profiling can all be used to allow older machines to accommodate these larger packages—albeit only to a certain extent.

Challenge #2: Neighboring Device Damage
Components in and around the rework area can be damaged during the rework process, as the heat sources typically used—both IR and hot air—can thermally damage neighboring components. Nearby components such as aluminum, tantalum and ceramic capacitors, crystals, oscillators, plastic-bodied components, and others need to be properly thermally shielded. LEDs and cameras can also be damaged at reflow temperatures.

Not only can these neighboring components be damaged when exposed to heat, they can also be sent into reflow if heating areas and temperature cycles are improperly controlled. This can cause heavier components to fall off the underside of the PCB during BGA rework. Furthermore, when solder is reflowed, the intermetallic formed in the solder fillet can grow, causing the component to form a weaker mechanical bond to the PCB.

With the use of the proper thermal shielding materials, these problems can be avoided1. Newer materials are now available to help protect components from both damage and reaching reflow temperatures. Thermal shielding materials such as water-absorbing cool gels, as well as ceramic non-wovens, are the most effective thermal shields.

Challenge #3: Underfilled BGA Rework
Underfill has made its way into a variety of industries, including automotive, military, and aerospace applications. Underfill boosts the reliability of the component, which is subject to mechanical impacts and shocks by distributing the forces. Thermal stresses caused by the coefficient of thermal expansion mismatch between the component and the PCB are also 

BobW_Feb_Fig1.jpglessened by using underfill. However, the proliferation of underfills has increased the need for solutions to underfill component rework. With underfill usage expected to grow over 5% per year through the next five years, finding appropriate solutions for underfill component rework issues will remain challenging2.

BGA rework locations neighboring the same or opposite side of the PCB can be damaged during the rework process. Since the underfill softens before reaching the solder’s liquidus temperature, underfills near the rework location can “push out” solder from its desired location, thereby creating soldering anomalies such as shorts or other soldering defects.

Another major rework challenge is breaking the BGA free from the underfill during the component removal process. During reflow, the tack of the underfill holds the BGA tightly to the PCB. Removing the BGA requires the rework technician to either “cut through” the underfill using a knife or to use specially designed nozzles to pull the BGA off the board. Either of these operations can result in damage to the PCB pads or solder mask. Once the BGA has been removed, this underfill material, as well as the remnant solder, needs to be manually cleaned from the board. This labor-intensive process is necessary to ensure that the site is adequately cleaned prior to replacement of the BGA.

Newer methods such as cold removal using a highly controlled milling process or laser ablation of the component can overcome some of these rework challenges. These advanced methods, while faster and repeatable, require both capital and higher-end programming and processing skills on the part of the rework supplier.

Challenge #4: Mirrored BGAs
When BGAs are placed “back-to-back” directly opposite one another on both sides of a double-sided PCB, the configuration is known as “mirroring” (Figure 2). This is a continuing challenge in BGA rework as board densities increase. In BGA rework, it is necessary to preheat the PCB from the opposite side of where the BGA is to be removed and replaced. This necessitates heating the BGA underneath the rework location causing the underside BGA to be exposed to a minimum of 125°C. In addition, this causes the underside BGA to be exposed to a longer duration heat cycle, which increases the potential for damaging or warping the BGA. It may also cause the underside component to go into reflow resulting in soldering anomalies and solder joint embrittlement. Another danger is the potential for larger more massive BGA components to “fall off” the oppositely located BGAs as the surface tension may no longer be able to overcome gravity, which is pulling down on the component.


The challenges for BGA rework will continue to evolve. Large BGA packages, BGAs in close proximity to neighboring devices, underfilled BGAs, and mirrored BGAs currently present the greatest challenges in BGA rework today.


  1. “Shielding Effectiveness of Polyimide Tape During Rework,” by Adam Gaynor and Bob Wettermann, Circuits Assembly Magazine, Oct. 1, 2014.
  2. “Electronic Board Level Underfill Material Market,” by Future Market Insights Global Consulting, 2022.

This column originally appeared in the February 2023 issue of SMT007 Magazine.



Knocking Down the Bone Pile: 2023’s Top Challenges in BGA Rework


Over seven years ago, I put pen to paper to enumerate the top challenges needing to be overcome for a successful BGA rework. With the continued advancement of BGA technology, it’s time to apply a fresh coat of paint to that list. Read on to find out my revised take on today’s top BGA rework challenges. As devices become more complex and computing power requirements increase, the maximum physical size of BGA packages has increased as well. Currently, some devices in development are planned to be 125 mm x 125 mm in size. These large package sizes present some very challenging scenarios for rework process technicians.

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


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


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


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


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


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


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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Knocking Down the Bone Pile: Methods for Underfilled Component Rework


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


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


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


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


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


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


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


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


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


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’


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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Knocking Down the Bone Pile: Electronics Assembly Industry Outlook


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


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


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


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


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?


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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Proper Thermal Shielding Yields Highest Rework Results


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


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


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


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'


"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


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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