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December 18, 2018

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 Panel Responses

I only haveexperience with Intrusive reflow pin in hole. In this case too big of apin to hole ratio leads to voids. 25 mil pin in 48 and 44 hole leas tovoids where 25 pin in 40 and 36 hole was OK. Maybe it is reversed forwave since wave must fill in around pin. For Intrusive reflow the pasteis 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, pinsize, thermal relief and more play a role. One company for smallelectrolytic caps with a .024 pin size use a 0.049 hole. A large electrolyticwith a 0.032 pin may require a 0.070 hole. There is an openproject by one of the consortia evaluating this question currently.

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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-sizeyour hole needs to be, you'll find a wide range of sometimes-conflictingresults. The reason is that some of the recommendations are focused onauto-insertion needs, while others are based on optimizing the soldering operation,and some incorporate both. To complicate matters, the solder alloy to be usedhas a big impact, as does the pin shape (round, square, flat). For a roundlead, if your diameter is 0.008" to 0.015" over the pin diameter, you'reprobably not in big trouble. Where the optimum lies depends on a lot ofvariables. Let's talk about what can impact flow-through:
  • Lack of adequate heat transfer up the lead and barrel. Both thebarrel and the lead must reach soldering temperature throughout the PWBthickness, or solder flow up the barrel will be halted. Problems can be causedby lack of lead protrusion, too many ground plane connections to the PTH orinsufficient thermal relief on ground connections, too low solder temperatureor too-short contact time.
  • Slow or absent wetting. Both the lead surface and the hole wallmust be made wettable by a flux in order for a capillary force to begenerated that will cause the solder to flow up the hole. Wetting problems canbe caused by poorly-solderable surface finishes, lack of flux penetration, orimproper pre-heat (either too-aggressive or insufficient), or contamination ofhole walls or leads.
Careful examinationof the partly-filled holes can be informative. Are holes on ground pins moreproblematic? 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 componentsmore susceptible? Can flux penetration be verified? The answers may guide youtoward 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.

Thisis a difficult number to find in the "standards." Ican tell you that board designers have a "rule of thumb" for the finished holediameter which is: 0.016" (0.4mm) larger that the component lead. This gives0.008" (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 39 years as a Senior Project Engineer. He has seen and worked with the electronic manufacturing industry from many points of view, including: technician, engineer, manufacture, and customer. His focus has been the design and application of measurement tools used to improve manufacturing thermal processes and well as moisture sensitive component storage solutions.

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 wouldsuggest 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 improvewetting.
Additional flux maybe accomplished by pre dipping the component leads in flux prior to boardplacement.

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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 temperaturemore flux

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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 willget plenty of practical advise from wave soldering experts. One thing Iwould like to introduce is the thought that it may not be necessary to wavesolder the component. It may be possible to reflow solder the throughhole component at the same time as the SMT components, using printed solderpaste. There are a few things to consider, such as peak temperaturecapability of the component and component standoff height to provide clearancefor the solder paste. Press fit or near press fit connectors don't reflowsolder well, since the solder needs a reasonable clearance to flow freelyduring reflow. The advantage is that 100% hole fill can be routinelyachieved, since issues such as temperature gradients top side verses bottomside, barrel connections to internal planes that act like heat sinks no longerapply, since the entire board achieves the same temperature while in the reflowoven. If there isn't enough board real estate to print sufficient soldervolume for each pin, solder preforms from tape and reel packaging can beconsidered as a method to augment the solder volume. The elimination ofwave soldering is a significant industry trend, and may represent the mostsignificant cost savings opportunity since low silver solder was introduced. It is worth examining, especially if you have a problematic board thatdoes 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 'itdepends.' The IPC has aninspection standard for finished assemblies and I think it is 610 off the topof my head, this will have different pass / fail standards depending on theclass 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 youwill measure this and X-ray is the only real way without cutting up theproduct.

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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


We have a Board Talk segment on this topic. See: http://www.circuitinsight.com/programs/54395.html

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Jim Hall
Principal Consultant
ITM Consulting
Jim has a wealth of knowledge in soldering and thermal technology, equipment and process basics and is a pioneer in the science of reflow technology.

Ensure sufficient flux wicking.
Ensure sufficient top side preheat BUT not too hot so as to burn off all the flux. So typically 100C Topside temperature just prior to wave.
Ensure PCB is deep enough in the solder.
Ensure Solder bath itself is hot enough to improve flow of the Solder while the heat sinks travels through. Typical Lead Free temperature is actually 275C setting on the wave

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Greg York
Technical Sales Manager
BLT Circuit Services Ltd
Greg York has over thirty two years of service in Electronics industry. York has installed over 600 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.

Reader Comment
I agree with most of the Expert Comments. Board thickness, pin to hole diameter ratio, pre-baking of boards, optimizing wave soldering profile play important roles in avoiding voids for making a good solder connections.
Ranganath Mandayam, TQM Consultancy