|Ask the Experts|
September 17, 2020
Exposed Copper Defect
Is exposed copper considered a class 3 defect per IPC-610 or J-STD documents?
|Expert Panel Responses|
That would depend on where the copper is exposed. Some component types normally have exposed copper where the packages are excised from lead-frames during fabrication.
Ex: QFNs. For the PCBs, copper exposed by solder mask or laminate defects would not be acceptable.
Principal Product Engineer
Benchmark Electronics, Inc.
No. Exposed copper is not considered a defect in J-Std-001 or IPC-A-610. It used to be defects ways back when - years ago.
A good example is use of OSP surface finish. All the copper pads don't get covered with solder even when the solder joint is perfect.
Ray Prasad Consultancy Group
Basically, so long as exposed copper or basis metal is not part of the required solder fillet area or the result of damage to leads, conductors, or lands that exceeds other requirements for lead or PWB damage, it is at worst, a process indicator for Class 3.
Exposed copper that is the result of cut leads or on vertical edges of a PWB conductor or land-not the result of damage and not part of the required solder fillet-is acceptable. If the exposed area is the result lead deformation or PWB damage that exceeds other requirements (section 7 for leads, section 10 for PWBs), it is a defect.
Manufacturing Process Engineer
No this is not considered a defective condition for any class of product. There are many conditions in the documents that state exposed basis material is an issue however this is all based upon damage to the components leads and the plating on the component leads, regardless of the basis material. Exposed copper is only a defect when it impacts the creation of the solder joint. Additionally is exposed copper was an issue then OSP coated boards would be a thing of the past and they are not.
Section 4.18.1 Exposed Surfaces, references the impact of basis materials, i.e., copper or equivalent, shall not impact the formation of acceptable solder connections.
The Space Addendum 001 GS states the same thing but also adds that the only materials which are not to be exposed are Alloy 42, Kovar, or any iron based materials. This is all due to the potential corrosion, i.e., rust.
IPC-A-610 references exposed ends of wires shall not be exposed in section 4.5.4, and this is due to potential exposure of the conductor to cause a short.
Section 5.2.1 Soldering Anomalies - Exposed Basis Metal states, "...Exposed basis metal or surface finishes should be considered normal under these circumstances, provided the achieved wetting characteristics of the solder connection areas are acceptable." This basically states the solder joint cannot be impacted by the expose material, however exposed copper is allowed on pads and the vertical edges of all conductors traces do not have to be covered and can be left exposed.
Exposed copper was not allowed the military years ago, however this was changed and it is now an acceptable condition. Some examples of exposed copper we should be aware of is the copper piping in homes and copper roofs on buildings. Many of those have been around for many years.
Vice President, Technical Director
IPC-A-610F section 5.2.1 Soldering anomalies - Exposed basis metal states that exposed base metal is acceptable for Class 1, 2, and 3 assemblies under certain conditions. The conditions include: vertical conductor edges, cut lead and wire ends, OSP coated pads, and exposed surface finishes that are not part of the required fillet area.
Nicks and scratches are a defect if they exceed the requirements of 18.104.22.168 and 10.3.1 which detail reduction of the conductor dimensions. If you don't have copies of IPC-A-610F and J-STD-001G then I suggest getting these standards.
YES: Exposed copper is a class 3 defect per IPC-A-600 EXCEPT for card edge connectors. Remember those?
Circuit Connect, Inc.
This could also be an assembly question. From IPC-6012 For areas that are not to be soldered, 1% of the conductor surface can be exposed copper (class 3) and 5% for class 1 and 2.
For solderable surfaces, exposed copper is not acceptable. Visible coverage and solderability must pass J_STD requirements.
Director of Marketing
Per IPC 610G 5.2.1 "Soldering Anomalies - Exposed Base Metal"
Some printed circuit board and conductor finishes have different wetting characteristics and may exhibit solder wetting only to specific areas. Exposed basis metal or surface finishes should be considered normal under these circumstances, provided the achieved wetting characteristics of the solder connection areas are acceptable. This applies to Class 1,2,3.
Technical Marketing Manager
Leaving exposed copper on a printed circuit board assembly is not recommend for any end application environment since copper quickly corrodes in most environments, potentially precipitating a failure. A solder mask touch-up can be used if the exposed copper is only in a very small area.
A better alternative is to apply conformal coating to eliminate the exposed copper using a conformal coating system since these systems have better control over the coverage area and thickness as opposed to manual brushing or manual aerosol spraying.
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