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中文The copper tape (copper foil) in the PCB (Printed Circuit Board) is the key carrier of current transmission, and its dislodgement will directly lead to circuit breakage, functional failure, and even lead to short-circuit or burnout.Copper strips are not accidental, but rather a concentration of design, material or process problems.Below are the three main causes that have been technically verified, dismantling each of the key factors from production to use.
1. Insufficient bonding between base material and copper foils
The bonding of copper tape to the PCB substrate relies on the adhesive layer (semi-cured sheet or special adhesive) between the substrate (e.g. FR-4 epoxy glass cloth laminate) and the copper foil.If the bonding force does not meet the standard requirements, the copper tape is prone to detachment in production or use.
Specific reasons:
- Improper surface treatment of the substrate: residual grease, oxide layer or dust on the surface of the substrate during production, the adhesive can’t fully infiltrate the surface of the substrate, resulting in a decrease in the bonding strength;
- Mismatch of semi-cured sheet parameters: the resin content, fluidity or gel time of the semi-cured sheet is not selected according to the requirements of the lamination process, and the adhesive layer is unevenly distributed or not fully cured after pressing;
- Lamination process out of control: Pressing temperature, pressure or time do not meet the process standards (e.g., insufficient temperature leads to insufficient melting of the resin, insufficient pressure leads to air bubbles), resulting in the formation of localised weak bonding areas between the copper foil and the substrate.
Typical performance: During drilling, milling or subsequent assembly, the copper strip peels off from the edge of the substrate or a specific area, exposing the substrate itself.
2. The performance of copper foil itself is not up to standard
The physical properties of copper foil (thickness, purity, ductility) directly affect its resistance to mechanical damage.If the quality of copper foil does not meet the design requirements, even if the process is correct, it may still fall off due to insufficient strength.
Specific reasons:
- Insufficient thickness of copper foil: the design documents require 1oz (about 35μm) of copper foil, but 5oz (about 18μm) of copper foil is actually used, resulting in insufficient mechanical strength of the copper strip, which is torn when drilling, welding or assembling;
- Internal defects in copper foils: cracks, holes or trapped metal impurities are created during the rolling process of copper foils, which break from the defects when subjected to force;
- Wrong type of copper foil: For example, flexible circuit boards (FPC) require the use of highly ductile calendered copper foils, but if hard electrolytic copper foils are mistakenly used, they are prone to cracking and peeling off in bending or vibration environments.
3. External damage during processing or use
The direct causation of copper strip detachment often comes from external mechanical action or environmental stress, especially high temperature, vibration or physical shock scenarios.
Specific causes:
- Drilling / milling damage: excessive speed of the drill when drilling, too large a feed, or milling tool wear, resulting in local overheating or mechanical stress concentration, the copper foil is scratched or torn;
- Welding high temperature impact: wave soldering or reflow soldering temperature exceeds the tolerance limit of copper foil and substrate (e.g. FR-4 substrate temperature resistance of about 280 ℃), the substrate and copper foil due to the difference in the coefficient of thermal expansion (CTE mismatch) resulting in internal stress, leading to delamination;
- Assembly/use stress: PCB installation screws are too tight, collision during assembly, or the product is in a vibration environment for a long time (e.g., automotive electronics, industrial equipment), the copper tape is fatigued off due to repeated stress.
Summaries
The core reasons for PCB copper strip shedding can be summarised as follows: insufficient combination of base material and copper foil (material and process problems), substandard performance of copper foil itself (material quality problems), external damage (processing or use problems).To solve the problem, it is necessary to control from the source – the surface cleanliness of the substrate, the matching of the parameters of the semi-cured sheet, and the parameters of the lamination process need to be in strict compliance with the standard; the procurement of copper foil needs to be verified for the thickness, type, and quality certification; the processing process needs to be standardised (e.g., controlling the drilling parameters, welding temperature), and the use of the process to avoid mechanical shock or extreme environmental exposure.Only by controlling the whole process can we effectively reduce the risk of copper strip shedding.
