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. The methods for hand soldering QFPs listed under IPC 7711 5.5 include the following:

  • Top of the lead
  • Point-to-point method
  • Solder paste method hot air system
  • Hook tip wire layover
  • Blade tip with wire solder
  • Adhesive-backed stencil with solder paste and hot air method
While these are a head-spinning number of techniques, the following discussion will compare the more widely used techniques: point-to-point, drag, and adhesive-backed stencil.


Point-to-Point Soldering
The point-to-point method is the one with the most history behind it. Point-to-point soldering is a manual soldering process in which individual solder connections are soldered one connection at a time (Figure 1). The method usually consists of using a chisel tip connected to the soldering hand piece. First, locate the correct tip. The size of the chisel tip should be such that it can properly create the “heat bridge” between the land and the component lead. A good rule of thumb is to have the tip 60–70% of the pad width. The component should be properly inspected to make sure the leads are coplanar and that they are not damaged and bent. Upon proper inspection, the component should be aligned with the pads and be held with a pair of tweezers or an orangewood stick. Next, liquid flux appropriate for the assembly is applied at two opposite corners and the component is tack-soldered in place such that it Wettermann_Aug_Fig2_cap.jpgdoes not move off the pads. Flux is applied to the remaining lead/land rows and creates a heat bridge between the land on the PCB, the soldering iron tip, and the component lead adding in solder to form the proper solder fillet. Finally, the fillets are inspected per the class required of the assembly.

Drag Soldering
Drag soldering is a manual soldering process that uses a special soldering iron tip with a concave surface “spoon” or “hoof” shape to hold molten solder (Figure 2). This ball of molten solder is then “dragged” across the leads of the QFP, letting the surface tension and natural wetting forces of the solder deposit the correct amount of solder on each of the leads. When using the drag soldering technique, it is most effective with multi-leaded, very-fine pitched components. As with the point-to-point soldering technique, make sure the opposite corners of a package are tacked into place such that the component is aligned and cannot be moved off the pads. Apply enough solder to cover approximately one-third of the tip. For finer pitch parts apply less solder. Now flux the leads on each side of the component. Start from a row that has not been tacked in position. Bring the tip down at an angle to the point where the tip of the lead meets the land so that the edge with the solder on it is on the land, but the face is tilted away from the component. Hold the tips so the shaft runs parallel to the row of the leads. The angle between the side of the tip and the side of the Wettermann_Aug_Fig3_cap.jpgcomponent can be up to 30 degrees (Figure 3) depending on operator preferences. Start running the tip down the toes of the leads. 

The variables to control are pressure (very light) and speed. The operator should glide across the leads with no pressure, with the speed determined by the thermal mass of the board. Follow this process on all sides, cleaning Wettermann_Aug_Fig4_cap.jpgand inspecting after soldering to the appropriate inspection criteria and class. Make sure the tip is tinned prior to putting it back into the holster. 

Adhesive-backed Stencil

In some applications, less experienced soldering technicians can place an adhesive-backed stencil and solder a fine-pitched gull wing device in place (Figure 4). To begin, make sure the site location is clean and dry prior to placing the adhesive-backed stencil. Peel the stencil from the release liner and align it with the lands on the PCB. Roll solder paste through the apertures of the stencil by using a small handheld squeegee (Figure 5). The squeegee can be moved back and forth several times before removing the stencil. Now carefully place the component onto the Wettermann_Aug_Fig5_cap.jpgbricks of the solder paste printed at the rework location. Reflow the solder paste using a hot air or infrared heat source. Clean and inspect per the guidelines of the work.

In the point-to-point soldering technique, a technician will be soldering each connection individually, which allows for adjustment of the applied heat, dwell time, and solder volume to suit each particular connection. This technique gives the technician a lot of discretion regarding the rework process, but also reduces the uniformity and consistency of the solder connections. The downside of the point-to-point soldering method is that it is time-consuming and tends to burn out tips more quickly.

In drag soldering, a highly skilled technician can move through components much more quickly. However, it is imperative to have a high-quality solder station and iron with active tip temperature monitoring and control, as well as plenty of liquid flux (may not be suitable for all applications). When done properly, the drag soldering technique results in more uniform solder fillets.

Finally, the stencil approach requires the use of a custom-made stencil while reducing the soldering skill level of the technician. Each of these methods can be used to effectively solder a QFP in place. The method chosen is a function of the soldering skill level of the technician and the pitch and lead count of the component.


  1. IPC 7711.21 Rework and Repair of Printed Circuit Assemblies, Revision C 2020.

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



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.

View Story

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.

View Story

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.

View Story

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.

View Story


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.

View Story

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 © 2022 I-Connect007. All rights reserved.