|Ask the Experts|
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?
|Expert Panel Responses|
J-STD-001 is the exact guidance for your requirements and will answer all of your questions.
Circuit Technology Center, Inc.
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.
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.
Senior Manufacturing Engineer
This looks like a condition referenced by IPC-A-610 paragraph 188.8.131.52 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.
PCBA Engineering Liaison
General Atomics Electromagnetic Systems Group
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.
Principal Product Engineer
Benchmark Electronics, Inc.
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.
Senior Quality Engineer - PCB Assembly
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