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. The 0201 package—only 20 by 10 thousands of an inch in size—is one of the components requiring a higher degree of rework skill compared to other larger packages. IPC-7711 and IPC-7721 on the “Rework, Modification, and Repair of Electronic Assemblies”[1] for these resistor and capacitor sizes outlines a variety of methods in sections 3.3.X. Here, I will compare and outline a few of these rework methods.
 
While the 0201 package size has been in the mainstream for several years, assembly soldering defects are common. Tombstone defects, common for this package type, are commonly caused by the pads heating up at different rates. A thermal mass imbalance may cause one of the pads to heat at a different rate compared to the other. For example, if one of the 0201 pads is connected to a thermal ground plane and the other pad is not, the unconnected pad will heat at a faster rate—all others being equal. This thermal imbalance will cause the tombstoning defect as the molten solder pushes up one side of the component. 
 
It is well understood that lighter and smaller components are more susceptible to this tombstoning phenomenon. A similar result is realized if the pads are not the same size, as the larger pad will heat at a slower rate. The pad sizes influence the defect rate; smaller pad sizes result in higher defect rates[2]. The component placement offsets in the X and Y direction are one of the largest contributors to the post-reflow defect rates of these packages. This means that the assembler needs to control these parameters by placement consistency through proper placement programming, nozzle maintenance, and placement pressure. In addition, the very small pad geometries of the 0201 packages make solder paste printing consistency a challenge, which can also cause defects.

A Conductive Soldering Rework Technique
The most common technique used to remove and replace 0201 body style components is through the use of a conductive hand soldering system. This hand soldering rework technique calls for the removal of a passive component by employing a micro body tweezer or a micro hoof soldering tip. For part removal using a micro hoof tip, make sure to first tin the flat surface of the tip as this will aid in heat transfer. For placement, apply the proper liquid flux to the pads and hold the 0201 down with the tip of a tweezer and touch the hoof tip for 2–3 seconds to one side of the pad to allow the solder to reflow. Finish the attachment by doing the same operation on the other side. 

An even faster hand soldering method uses a micro tweezer hand piece. These tweezers can reflow both ends of the 0201 simultaneously for component removal or replacement. The tips themselves are fragile structures and are easily damaged, which means care needs to be taken by the soldering technician. Because of the small geometries involved, the skill and patience of the soldering technician need to be at an advanced level. The site preparation process post component removal, regardless of the tip used, requires great care by the rework technician as the very small pad surface area means that the propensity to damage or lift pads is high. While hand soldering is the fastest method for the removal and replacement of the 0201, it requires a high degree of operator skill and dexterity.

Hot Air Rework
Another reflow method employed by soldering technicians for the rework of these small passive devices is by using a hot air source. Both controlled (closed-loop rework systems) and uncontrolled hot air sources (hot air guns or handpieces) can be used to reflow 0201s. These hot air sources must be designed with low airflow capability so as not to disturb the solder joint or blow the component off the pad. A controlled heat source has limited throughput compared to the hand soldering rework method as there are several process steps, which takes time. A split vision rework system, which assists the operator in aligning the part to the pads, reduces the degree of skill required to rework these small packages. 

The downside of using a hot air reflow source is that components neighboring the component of interest can also be reflowed during the soldering or desoldering process. To prevent the hot air source from disturbing these neighboring components, they need to be thermally masked from the heat source. This further extends the rework process time. When using a hot air rework system, the removal of the component is accomplished by using a hot air nozzle specifically designed to push out low airflow. For replacement of the 0201 component, a high-resolution camera, combined with precision X-Y adjustments of the rework system, means device placement can be more precise and repeatable vis-à-vis the hand soldering approach.

Using an IR Reflow Source
While the hand soldering of 0201 packages requires highly-skilled soldering technicians and the hot air rework sources can easily disturb the solder or placement location of the lightweight 0201s, the use of an IR reflow source is a good alternative approach to reworking these packages. Infrared rework systems do not use any airflow as part of the reflow cycle, thereby preventing the problems associated with the hot air rework sources. The IR heat source can quickly heat these small component body style types before their removal. 

Magnification, as part of the rework system—along with a micro vacuum nozzle—can then remove the component once a liquidus state has been reached. Through the use of an IR BGA rework system and the high skill and dexterity level required for rework of these 0201 packages, without the downside risk of the positive airflow from the hot air source, makes the IR reflow source ideal for these components.  
 
References
1. IPC, “IPC-7351 Generic Requirements for Surface-Mount Design and Land Pattern Standard,” Bannockburn, Illionis, 2015.
2. Paul Neathway, et al. “A Study of 0201’s and Tombstoning in Lead-Free Systems,” Proceedings of SMTAI, 2014.

This column originally appeared in the September 2020 issue of SMT007 Magazine.

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2020

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

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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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