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December 12, 2018

Test for Flux Penetration

What is good test for flux penetration through the plated hole barrel?

J.V.

Expert Panel Responses

Flux penetration isimportant to the flow of solder up into the plated through hole. The elements which need tobe inspected are Flux coverage on the solder source side and flux penetrationthrough the plated through holes. You can use a glass plateto check for flux coverage on the bottom side of the board. For the platedthrough hole penetration, use a raw board and apply a thin sheet of absorbentpaper on the top side of the board and process it through the fluxer system.You should be looking for flux residues on the absorbent paper sheet. Also lookfor flux around the pads on the top side of the board. Aspecific area to be cautious of is the edges, make sure the flux penetrates thehole near the edges of the board to make sure you get good solder flow in thoseholes.

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Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.

Thetried and true method is to lay a flux sensitive paper over an unpopulatedboard and pass it over your machine's fluxer. Good penetration will show on thesensitive paper as a discoloration of the paper over (top side) each hole. Thesensitive paper may be: pH paper, fax paper, or even a thin brown cardboardstock to see if wetting occurred over the desired holes. The fax and pH papersare nice because they hold the color change while the simple card stock paperwill dry fast and thus NOT be a permanent record. The type of paper depends onthe flux used and its characteristics: acidity (pH), IPA content, etc. There are generaltools available for testing flux penetration such as the Fluxometer(r), whichuses the method described above, with a "mesh" board to check for uniform fluxpenetration over the entire fluxed area.

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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.

What we used to do was to use a plate with perforations ofvarious sizes arranged in a pattern that repeated on a grid. Over the plate isplaced a sheet of paper(1) which is sensitive to the flux and provides a visualindication of contact with the flux. Over that sheet is placed a solid sheet tokeep the paper in contact with the perforated plate. The entire "sandwich" issent through the fluxer, but not the rest of the process. The paper is examinedfor penetration. The variation in penetration with respect to hole size(2) andin across-conveyor and along-conveyor directions, can be analyzed.Devices similar to the above may be available as a package; wedeveloped and built or own, based on our specific needs.
  1. For alcohol-based fluxes, FAX paper(thermal paper) was used, as the alcohol triggered a blue-black colortransition that was clearly visible. This paper is not as common as it used tobe, but should still be available. For water-based fluxes, typically apH-reactive paper is used.
  2. The range of holesizes used must include holes that are small enough to simulate the behavior ofa larger hole with a lead inserted. While the behavior of a smaller, open holeis not identical, it is an acceptable proxy.


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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.

Youcan use a paper on top of the board that is reactive to your specificflux. This is the same method as we (ECD) uses on our Fluxometer product,and paper can be sourced from us directly.

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Mark Waterman
M.O.L.E. Line Product Manager
Electronic Controls Design, Inc. (ECD)
Mark Waterman is a trainer and field engineer with 17 years experience in service and applications specialties. Intimate knowledge of soldering processes and measurement systems. Six sigma and statistical process control generalist.

Yes there is a simplevisual test, unfortunately the test is only completed on bear PCB boardsso it will not produce 100% the side effects of having components in a hole.But the test is useful and helpful to users. The test uses eitherthermal fax paper for alcohol based fluxes or pH litmus paper for water basedfluxes. The user would then place and secure the test paper down to thetopside of a bear assembly and process the vehicle through the fluxer process. The flux atomized spray that penetrated the holes in the PCB would leavea visual imprint on the appropriate test paper that was used. Also thereis a test vehicle offered today in the market place by ECD called aFlux-O-Meter. This unit consists of a test vehicle PCB, a pallet with ahold down unit and the proper tets papers. I hope this information ishelpful to you.

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John Norton
Eastern Manager
Vitronics Soltec
John Norton started his soldering career in 1983 for Hollis Engineering. He has also worked with Electrovert as a technical training manager and Vitronics Soltec for the last ten years. He has held various technical development and sales positions.