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. X-ray imaging of the actual BGA location, as well as the surrounding area, is used to confirm rework challenges such as the proximity of neighboring devices, starved solder joints, and solder balls causing electrical shorts. These images can point to potential root causes for the BGA rework including broken bond wires,  or the popcorning or delamination of the package. Furthermore, soldering anomalies such as head-in-pillow or graping defects, which may be causing intermittent connections, can be the cause of the failure. Devices on the opposite side of the BGA location will determine potential problem areas due to heat effects of the rework process.

For example, if a BGA is underneath a shield, X-ray will help determine the location of the BGA and the neighboring devices, as well as the margins for getting a nozzle into the rework location (if using a hot air rework reflow source). X-ray imaging will also provide clues to the physical board problems such as lifted pads or solder that has wicked down the dog bone of the PCB due to mask damage, as well as other anomalies.

Not only does X-ray imaging provide some clues prior to rework of some of the challenges that may lie ahead, but it also confirms that the rework was completed correctly. After visual and endoscopic inspection has been completed, the BGA rework location is inspected by manipulating the controls of the X-ray to where the component of interest is seen in a large field of view. The technician then manipulates the X-ray system to where numerous solder balls can be seen on the screen as the rows are scanned back and forth. The technician reviews the overall ball sizes to make sure they are consistent in size and shape.

Wettermann_Fig1_cap (2).jpgAnomalies such as small balls (Figure 1), oversized balls (Figure 2), and misshapen balls all will be caught by an experienced X-ray operator. Especially critical to observe are the corner solder ball locations. If these locations are full and round, then as a rule the overall ball collapse is sufficient. Smaller-sized balls may be a direct result of solder wetting down a dog bone pattern where the mask has been damaged, or in cases where a thermal via has wicked the solder down into the via hole. Oversized balls may be a result of neighboring balls having their solder squirt over to a neighboring ball location.

Wettermann_Fig2_cap (2).jpgWettermann_Fig3_cap.jpgObvious anomalies like solder shorts, missing balls, or misshapen balls will also be picked out during this part of the investigation. At this field of view the technician will next investigate areas around the device of interest. Skewed components, solder balls, or handling damage can all be picked up by examining the X-ray image. Solder may have “squirted” out of neighboring locations; such is the case when the board has been conformally coated or neighboring or mirrored devices that are underfilled also show up clearly on X-ray images. Once this larger field of view inspection has been successfully completed, the BGA technician zooms in to review details about the solder balls and their collapse. The technician is looking for misshapen balls, smaller or larger balls, a high voiding percentage, and solder shorts as well as numerous other anomalies. X-ray imaging really is a necessity to “see” these defects and anomalies after BGA replacement.

X-ray inspection of reworked BGAs prior to the rework operation, and both far and near field analysis of the X-ray images, are important to confirm that the BGA rework process has yielded success. Without the use of X-ray imaging, it is very difficult to confirm that the inspection criteria have been satisfied.


IPC-7095 Design and Assembly Process Implementation for BGAs

IPC-A-610H Acceptability of Printed Wiring Boards

This column originally appeared in the September 2021 issue of SMT007 Magazine.



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.

View Story

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.

View Story

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.

View Story

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.

View Story

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.

View Story


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.

View Story

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.

View Story

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.

View Story

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.

View Story

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.

View Story


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.

View Story

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.

View Story

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.

View Story

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.

View Story

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.

View Story

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.

View Story


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.

View Story

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.

View Story

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.

View Story

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.

View Story

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.

View Story

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.

View Story
Copyright © 2021 I-Connect007. All rights reserved.