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, and 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 is “surface mount center ground connector.” 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.

Wettermann_May_Fig1_cap.jpgThe rework of a component such as this requires that the assembly be handled by keeping in mind ESD 2020 guidelines for static control, including but not limited to operator grounding, proper packaging, and proper keep-out zones with respect to insulators that can generate and/or hold an electrostatic charge.

Wettermann_May_Fig2_cap.jpgWhen components such as this (Figure 2) are connected to a ground plane, it is imperative that the right amount of heat be imparted to the component during the removal process, especially when connected to a large ground plane. After properly supporting the assembly in the rework system, apply paste flux with your preferred chemistry to the component leads. The next step is making sure that the neighboring components are shielded to make sure all the components which need to be are thermally shielded. Components to be particularly watchful of include (but are not limited to) plastic-bodied connectors, ceramic capacitors, LEDs, glass bodied fuses, and others which are near the rework area. Make sure to examine the side opposite of the component to protect neighboring components from thermal damage prior to using heat to remove the component.

Prior to removing the component, it is always good practice to develop a profile board. In a profile board, thermocouples are embedded in key locations at and around the component location (on a process development board) to measure board and soldering temperatures at various locations. Typical locations to place these thermocouples are at the ground plane pad and at least two locations opposite one another on the connector. More thermocouples may be added at locations near heat-sensitive devices.

The rework removal profile can be more aggressive than typical reflow norms since in most cases, the component will be scrapped. Make sure the bottom side of the board is between125–150°C through heating of a bottom heater. Both IR and hot air sources can be used as a rework heat source. When profiling, make sure that the solder has turned into the liquidus phase by carefully observing the component either on the video feed provided by the rework station or by carefully peering at the solder/board interface using a flashlight. Once you can observe that the solder has obtained the liquidus state, activate the removal cycle and pick up the connector.

As in other area array or more complex component rework processes, after the assembly comes down to room temperature it is time to prep the site by wicking solder from the pads and cleaning the location. Finally, the pads should be inspected for damage.

For these component body styles it is best to use a miniature stencil or a programmable solder paste dispenser to affix the replacement connector to the PCB. The adhesive-backed stencil method is the least time-consuming method for selectively re-applying solder paste to the pads. The center ground pattern may need to be “window paned” to prevent too much solder from “lifting up” the connector leads. After peeling off the release liner from the stencil, align the stencil apertures, starting at one of the corners. Make the final fine alignment adjustments taking advantage of the repositionable adhesive which will keep also serve to affix the stencil into place once aligned. Using a small squeegee, roll solder paste through the apertures and then slowly peel up the stencil making sure it is perpendicular to the board surface. Examine the solder “bricks” formed on the PCB to make sure the solder paste has been applied to all locations consistently.

Another approach for stenciling is to use a “mini” stainless stencil that mimics the original stencil design at the rework location. This technique takes a great deal more skill to get right and not “smear” the solder paste. A programmable dispenser, while taking some time to set up and program, will also provide for a consistent solder paste volume at each of the pads. After the solder paste is deposited, place the PCB onto the rework station making sure the PCB is properly supported. Recall the proper reflow profile in the rework station and begin the reflow cycle.

After reflow, a few more steps need to be taken to compete the rework process. After the board has cooled and the assembly has been removed from the rework machine, the rework area needs to be cleaned and then visually inspected per the IPC-A-610 standards. Since the ground connection is a non-inspectable area of the connector, this rework needs to be placed into an X-ray machine in order to confirm the solder connection of the component to the PCB. Final inspection also includes the “fit up” with a header that will plug into the receptable on the board to make sure that the connector will function properly and has not been damaged in the rework process.

While the rework of high density SMT connectors with ground planes is challenging, the right process with the right controls in place and completed with properly trained personal will provide for a high yield.

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



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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