|Ask the Experts|
February 15, 2021
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?
|Expert 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.
Vice President Technology
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.
Chairman of the IPC Technology Roadmap Committee
Interconnect. Technology Analysis Inc.
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:
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.
Senior Project Engineer
Electronic Controls Design Inc
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:
Minco Products Inc
Guidance from IPC-2222 Revision A
For better fill, some possible solutions are:a slower conveyor speed on the wave solder a higher operating temperature more flux.
Lockheed Martin Space Systems
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 longerapply, 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.
Global Product Manager
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.
Global Product Champion
Check all the above recommendations, perform a solder bath analysis. Consult with your solder, flux and equipment manufactures for assistance.Mark A Maheux Sr., Honeywell
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!
We have a Board Talk segment on this topic.
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
Technical Sales Manager
BLT Circuit Services Ltd
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
Be careful, as too large of a hole, even a few thousands, is much worse than too small. If the aspect ration of the plated hole/lead is too large, the surface tension of the molten wave solder can be greater than the surface tension of the wetted solder, and will pull it right back down. This makes a bad design even worse.Ricardo Stademzuela, ElectroMex Inc.
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