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Insufficient Barrel Fill on Through-hole Components
We are seeing insufficient barrel fill during wave soldering. What could we do to improve the barrel fill?
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Insufficient Barrel Fill on Through-hole Components
We are seeing insufficient barrel fill for one through-hole components during wave soldering. We suspect the problem could due to the pin-hole ratio being too small. Can you point us to a guideline for the recommended through-hole component/hole diameter ratio? What could we do to improve the barrel fill?
CM
Expert's Panel Responses
I only have experience with Intrusive reflow pin in hole. In this case too big of a pin to hole ratio leads to voids. 25 mil pin in 48 and 44 hole leas to voids where 25 pin in 40 and 36 hole was OK. Maybe it is reversed for wave since wave must fill in around pin. For Intrusive reflow the paste is already in the hole.
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Bill Coleman
Vice President Technology
Photo Stencil
For over 18 years, Dr. Coleman has been the vice president of technology for Photo Stencil, working closely with customers to understand their printing requirements. His efforts have resulted in several new stencil products.
It is very hard to answer this question. Board thickness, pin size, thermal relief and more play a role. One company for  small electrolytic caps with a .024 pin size use a 0.049 hole. A large electrolytic with a 0.032 pin may require a 0.070 hole.  

There is an open project by one of the consortia evaluating this question currently.
Jack Fisher
Chairman of the IPC Technology Roadmap Committee
Interconnect. Technology Analysis Inc.
Jack Fisher is a retired IBM executive, chairman of the roadmap since 1994, and member of IPC Hall of Fame.
If you search for generic recommendations on how much over-size your hole needs to be, you'll find a wide range of sometimes-conflicting results. The reason is that some of the recommendations are focused on auto-insertion needs, while others are based on optimizing the soldering operation, and some incorporate both. To complicate matters, the solder alloy to be used has a big impact, as does the pin shape (round, square, flat). For a round lead, if your diameter is 0.008" to 0.015" over the pin diameter, you're probably not in big trouble. Where the optimum lies depends on a lot of variables.

Let's talk about what can impact flow-through:
  • Lack of adequate heat transfer up the lead and barrel. Both the barrel and the lead must reach soldering temperature throughout the PWB thickness, or solder flow up the barrel will be halted. Problems can be caused by lack of lead protrusion, too many ground plane connections to the PTH or insufficient thermal relief on ground connections, too low solder temperature or too-short contact time.
  • Slow or absent wetting. Both the lead surface and the hole wall must be made wettable by  a flux in order for a capillary force to be generated that will cause the solder to flow up the hole. Wetting problems can be caused by poorly-solderable surface finishes, lack of flux penetration, or improper pre-heat (either too-aggressive or insufficient), or contamination of hole walls or leads.
Careful examination of the partly-filled holes can be informative. Are holes on ground pins more problematic? Is there evidence of wetting (low contact angle)to the hole wall, but a high contact angle to the lead, or vice versa? Are particular components more susceptible? Can flux penetration be verified? The answers may guide you toward one or more root causes.
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Fritz Byle
Process Engineer
Astronautics
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.
This is a difficult number to find in the "standards."

I can tell you that board designers have a "rule of thumb" for the finished hole diameter which is: 0.016" (0.4mm) larger that the component lead. This gives 0.008" (0.2mm) clearance around the component lead for solder to wick.

As for the standards, the IPC would be the best place to search for this information.
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Paul Austen
Senior Project Engineer
Electronic Controls Design Inc
Paul been with Electronic Controls Design Inc. (ECD) in Milwaukie, Oregon for over 34 years as a Senior Project Engineer. He has seen and worked with the electronic manufacturing industry from many points of view, including: technician, designer, manufacture, and customer. His focus has been the design and application of thermal process measurement tools used to improve manufacturing processes like: mass reflow and wave soldering, bread baking, paint and powder curing, metal heat treatment and more.
Circuit community recommendations range from .005" to .020" with .015" being commonly listed as a target.

Given that you need to play the hand you are dealt, I would suggest a couple of strategies for the existing boards:
  1. Preheat the board if possible to eliminate thermal lag
  2. Pre-tin the component to improve wetting speed
  3. Use additional flux to improve capillary action and improve wetting.  
Additional flux may be accomplished by pre dipping the component leads in flux prior to board placement.
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Nick Koop
Product Manager
Minco Products Inc
Nick has been in the circuit industry since 1985, in technical and management roles. Nick is the Vice Chair of the IPC Flexible Circuits Committee, and Chair of IPC 6013 Flexible Circuits Perfomance Subcommittee. Nick holds a Bachelors Degree in Mechanical Engineering and a Masters Degree in the Management of Technology from the University of Minnesota.
Guidance from IPC-2222 Revision A
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For better fill, some possible solutions are: a slower conveyor speed on the wave solder a higher operating temperature more flux
Mike Green
Design Engineering
Lockheed Martin Space Systems
Mike Green is co-chairman of the IPC Terms and Definitions Committee. He has been working with board design and manufacturing for 33 years.
I am sure you will get plenty of practical advise from wave soldering experts. One thing I would like to introduce is the thought that it may not be necessary to wave solder the component. It may be possible to reflow solder the through hole component at the same time as the SMT components, using printed solder paste.

There are a few things to consider, such as peak temperature capability of the component and component standoff height to provide clearance for the solder paste. Press fit or near press fit connectors don't reflow solder well, since the solder needs a reasonable clearance to flow freely during reflow. The advantage is that 100% hole fill can be routinely achieved, since issues such as temperature gradients top side verses bottom side, barrel connections to internal planes that act like heat sinks no longer apply, since the entire board achieves the same temperature while in the reflow oven.

If there isn't enough board real estate to print sufficient solder volume for each pin, solder preforms from tape and reel packaging can be considered as a method to augment the solder volume. The elimination of wave soldering is a significant industry trend, and may represent the most significant cost savings opportunity since low silver solder was introduced. It is worth examining, especially if you have a problematic board that does not achieve sufficient hole fill with the wave process.
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Paul J. Koep
Global Product Manager
Alpha
Mr. Koep is responsible for product planning and technical marketing for the Preform Products at Alpha. He is the co-author of several patents in the areas of soldering applications focusing on reflow and alternative methods.
The answer is 'it depends.'

The IPC has an inspection standard for finished assemblies and I think it is 610 off the top of my head, this will have different pass / fail standards depending on the class of product you are producing, but generally this will range from 60 - 100% depending on what you are producing. You then need to determine how you will measure this and X-ray is the only real way without cutting up the product.
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Richard Boyle
Global Product Champion
Henkel Electronics
Richard Boyle is a Global Product Champion at Henkel Electronics. He has over 25 years experience in the electronics assembly industry and is responsible for the global technical service of all of Henkel's solder materials.
Reader Comment
Check all the above recommendations, perform a solder bath analysis. Consult with your solder, flux and equipment manufactures for assistance. Note: if the copper level gets to 50% of max. - perform a copper removal program. Your solder manufacturer can help you if you have never done this. If it was working find out what changed. Good Luck!
Mark A Maheux Sr., Honeywell
Reader Comment

Inerting and controlling the atmosphere quality will improve wettability (less metal corrosion) and improve barrel filling. Hot nitrogen gives an extra help. Less flux and so cleaner PC boards at the end. Better heat transfer will give you the possibility to improve yield. More speed for conveyor, less pressure for solder pumps.

Luiz Felipe Rodrigues, Air Liquide, Brazil
Reader Comment

DIVSYS laboratory is frequently asked about flow-thru on component holes. Most of our customers have come from forensic testing that we have performed on such issues as flow-thru. In a majority of the cross sections we have performed on assemblies (at customer request), the number one cause for flow-thru issues has been insufficient copper in the plated hole. As a current seller of printed circuit boards, and an extensive background in the PCB Fab and Assembly world, I am floored by how many boards are sent to our lab for testing by customers that have low copper in the holes or poor hole wall construction from their present supplier. Let's eliminate the board as a reason for your issues before you go chasing problems on your manufacturing floor.

Tammie Fish, DIVSYS International, LLC, USA
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