Copper foil detachment (commonly known as "copper throwing") is a defect in PCB production. PCB manufacturers often attribute this issue to problems with the laminate and may request that the laminate supplier cover the losses. Based on customer complaint handling experience, the common causes of copper foil detachment in PCBs include:
I. Process Factors in PCB Manufacturing
1. Excessive Copper Foil Etching: Electrolytic copper foil used in the market is typically single-sided zinc-plated (commonly known as gray foil) or single-sided copper-plated (commonly known as red foil). Copper foil detachment is more common in zinc-plated copper foils thicker than 70µm, while red foil and gray foil thinner than 18µm generally do not experience widespread detachment.
- If the etching parameters are not adjusted after changing the copper foil specifications, the copper foil may stay in the etching solution for too long. Since zinc is an active metal, prolonged exposure to the etching solution during the PCB process can cause excessive side etching, leading to the detachment of thin copper lines from the substrate.
- Another scenario occurs when there is no issue with the etching parameters, but poor post-etching cleaning and drying cause the copper lines to remain surrounded by residual etching solution. Over time, this leads to excessive side etching and copper detachment, particularly in fine lines.
2. Mechanical Impact During Production: Localized collisions during the PCB manufacturing process can cause copper lines to detach due to external mechanical forces. This defect is characterized by copper lines with visible distortion or directional scratches and impact marks. The copper foil's adhesion strength is usually normal, and there is no sign of side etching.
3. Unreasonable PCB Design: Designing overly fine lines with thick copper foil can result in excessive etching and copper detachment.
II. Laminate Process Causes
Under normal conditions, once the laminate's hot-pressing stage exceeds 30 minutes, the copper foil and the prepreg combine completely. Therefore, pressing generally does not affect the bonding strength between the copper foil and the substrate. However, if the prepreg is contaminated or the copper foil's roughened surface is damaged during the laminate stacking process, the bonding strength may be insufficient, leading to localized or sporadic copper detachment.
III. Raw Material Causes of the Laminate
1. Issues with Electrolytic Copper Foil: Standard electrolytic copper foil is typically treated with zinc or copper plating on the rough side. If there are abnormalities in the copper foil's production or defects in the zinc/copper plating, the copper foil's peeling strength may be insufficient. When subjected to external forces during electronic assembly, copper lines may detach.
2. Poor Compatibility Between Copper Foil and Resin: Some special laminate materials, such as HTg (heat-resistant) laminates, use different resin systems, typically PN resins with simpler molecular structures and lower crosslinking degrees. These require copper foil with specific properties. If the copper foil used in the laminate production is not compatible with the resin system, the metal foil's peeling strength may be insufficient, leading to copper detachment during assembly.
