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April 27, 2021

Acceptability Standard for Plated Hole Barrel Fill

We are increasingly required to place devices with mixed pin technology having both surface mount and through hole pins onto boards that are thicker than the through hole pin length.

An example of this is a connector with a 0.75mm through hole pin length onto a 1.6mm board thickness.

What is the acceptability standard for barrel fill for this type of situation?

M.E.

Expert Panel Responses

J-STD-001 is the exact guidance for your requirements and will answer all of your questions.

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David Cormier
Engineering Manager
Circuit Technology Center, Inc.
Manufacturing Engineer of 20+ years. Involved in Industries relating to all sectors of defense, Commercial product Industries, RF - Microwave and Semiconductor industries. Vast knowledge and experience relating Mil-STD’s, IPC-STD’s, EAI-STD’s, GEIA-STD’s, J-STD’s and MIL-PRF-STD’s.

I recently had this situation. IPC specifies 100% barrel fill is the target, the minimum is 75% depending on the classification. I used a pin and paste stencil to provide fill from the "component" side and then backfilled with selective solder or hand solder.

With all the high frequency assemblies, anything less than 100% can vary the impedance and affect performance. I was fortunate, the connector in this case was offered with longer leads so I changed to that part. You may want to check if longer leads are offered.

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Larry Harman
SMT Engineer
ACDi
Mr. Harman is an SMT Engineer at ACDi and worked at Oven Industries as a Manufacturing Engineer. H's worked at Philips manufacturing ultrasound probes/circuitry. He holds three patents, one for an ultrasound probe design, and two for innovative rat/mouse zapper circuits. He attended Pennsylvania State University for Electrical Engineering.

Per J-STD-001F; "For components having pre-established lead lengths that are less than the board thickness, and the component or lead shoulders are flushed to the board surface, the lead end is not required to be visible in the subsequent solder connection."

Please consider that this statement will need to be discussed with your end customer. There is a potential for performing additional tests to determine reliability.

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Edithel Marietti
Senior Manufacturing Engineer
Northrop Grumman
Edithel is a chemical engineer with 20 year experience in manufacturing & process development for electronic contract manufacturers in US as well as some major OEM's. Involved in SMT, Reflow, Wave and other assembly operations entailing conformal coating and robotics.

This looks like a condition referenced by IPC-A-610 paragraph 1.5.1.7 on Specialized Designs, "where an industry consensus document cannot address all of the possible component and product design combinations." Customer involvement or consent may be needed for a definition for acceptance.

The PTH connections that go through the board and lock are retention features, but a metallic pin going through a plated through hole is likely there for alignment and maybe some reinforcement. 75% hole fill will be more difficult to achieve without the lead protrusion assisting the flow of solder into the hole.

Selective or Wave solder processes should be able to fill the hole adequately, though if these are connected directly to a ground plane it may take a longer dwell time. Evidence of wetting in the hole should hold the pins securely, but agreement with the customer on criteria may ultimately be required.

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Kevin Mobley
PCBA Engineering Liaison
General Atomics Electromagnetic Systems Group
Kevin has over 30 years of experience in process and manufacturing engineering serving in both EMS and OEM companies. Expertise includes all aspects of SMT as well as wave solder and CCA materials such as PCBs, solder material, and component finishes. Kevin has developed processes for thousands of assemblies from stencil printing to conformal coating and testing.

Your question raises many more questions: What acceptability standard (and class) are you required to use? IPC-A-610 and J-STD-001 are the most common. Does your customer have their own workmanship standard or specification? Your customer's specified requirements will generally supersede the industry standards. Are the through-holes supported or unsupported?

What is the lead-count of the components? Barrel fill requirements can vary based on lead-count and class. You should also consider that you may get 100% barrel fill with short leads, but not meet requirements for lead protrusion. I would recommend that you ask the customer or design owner to create a specific workmanship requirement for the product.

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Rick Kompelien
Principal Product Engineer
Benchmark Electronics, Inc.
27 years experience working with electronic and electro-mechanical manufacturing and design (medical, automotive, military, computer, and industrial controls). Military veteran - served as a Combat Engineer with the United States Marine Corps.

Since the connector have mixed pin technology - you probably aim to use pin-in-paste as a means to mount and solder them. While there are no standard specifically handling PiP, the closest we get is IPC-A-610 and their note about manufacturer's pre-established lead lengths that are less than board thickness.

Now, even if PiP are through-hole components, their solder source side are the opposite side compared to normal through hole wave soldering and the PiP process doesn't really need the protrusion of the pin for the initial wetting.
Since the component pins does not protrude, the optimum condition would be that they are covered inside the barrel (no need to fill the open part of the hole) with good wetting and no voids.

If it is the first time implementing this I would also apart from normal x-ray also verify it by cross-section and maybe a pull test (especially if the connector is a type that is continuously plugged in and out).

In many cases it can be beneficial to use pins that is shorter than the board thickness and there are several studies done that shows an acceptable reliability.

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Anki Forsberg
Senior Quality Engineer - PCB Assembly
Axis Communications
Over 27 years of experience within the PCB assembly area. Hands on experience troubleshooting SMT on a global basis as well as implementing and setting up new processes/technology/equipment. ESD questions is also a key area.
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