Electrolytic copper foil is a copper foil formed by the reduction and deposition of copper ions on the surface of the cathode in a solution containing electrolytes such as copper sulfate, using copper as the anode and stainless steel or titanium as the cathode in a specialized electrolysis equipment, under the action of an electric field. It is a thin pure copper foil with a thickness typically ranging from a few micrometers to over a hundred micrometers.

Electrolytic copper foil lamination is an important process in the manufacturing of printed circuit boards (PCBs). It is the process of tightly bonding electrolytic copper foil with other materials (such as insulation layers, inner circuit boards, etc.) under certain temperature, pressure, and time conditions through bonding materials (such as resins, etc.).

The main reasons for small holes in electrolytic copper foil during the lamination process are:

1、 Copper foil quality issues

1. Pinhole defect

During the production process of electrolytic copper foil, if there are impurities in the electrolyte, such as metal ion impurities (such as iron, zinc, etc.), these impurities may co deposit with copper during the electrolysis process. When the copper deposition around impurity particles is uneven, pinholes are easily formed.

During the compression process, these pinholes may develop into small holes due to pressure and compression from other materials. In addition, uneven current density during the electrolysis process can also lead to uneven crystallization of copper foil. The rough areas of local crystallization may have small gaps, similar to pinholes, which are prone to rupture during compression.

2. Insufficient toughness of copper foil

The purity of copper foil raw materials and production process will affect its toughness. If the purity of the copper foil is not high enough and contains a lot of harmful impurities (such as high oxygen content), it will reduce the toughness of the copper foil. During the lamination process, copper foil with poor toughness is prone to cracking and forming small holes due to the pressure of the lamination machine and friction with other materials.

3. Uneven thickness of copper foil

During the production process of electrolytic copper foil, differences in copper foil thickness may occur due to factors such as equipment accuracy issues or uneven electrolyte flow. During the compression process, thinner areas have relatively weaker ability to withstand pressure and are prone to rupture under pressure, resulting in small holes.

2、 Pressure bonding process issues

1. Excessive pressure

If the pressure setting of the laminating machine is too high, exceeding the ultimate strength that the copper foil can withstand, the copper foil will be crushed and small holes will appear. Especially when laminating multi-layer boards, if the distribution of pressure between each layer is uneven, this situation is more likely to occur in areas with excessive local pressure.

2. Improper temperature control

During the lamination process, an appropriate temperature facilitates the flow and curing of bonding materials such as resin, allowing copper foil to better bond with other materials.

If the temperature is too high, the resin may flow excessively, resulting in uneven stress on the copper foil during the bonding process. At the same time, high temperature may also cause changes in the properties of the copper foil itself (such as being more prone to deformation and cracking after softening); When the temperature is too low, the resin cannot flow fully, which will affect the bonding effect and create gaps between the copper foil and other materials. In the subsequent processing or use process, due to external forces, the copper foil at these gaps is prone to rupture and produce small holes.

3. Unreasonable pressing time

The pressing time is too short, and the bonding materials such as resin cannot be fully cured, resulting in insufficient bonding strength between copper foil and other materials. In subsequent processing steps or when subjected to external forces, copper foil is prone to separation from other materials, and small holes may occur during the separation process. On the contrary, a long pressing time may cause the copper foil to be exposed to high temperature and pressure for a long time, increasing the risk of copper foil cracking.

3、 Matching issues with other materials

1. Adhesive material issues

If the resin material used for bonding copper foil is of poor quality, such as bubbles, impurities, or incomplete curing in the resin, it will affect its bonding performance. When the bonding strength is insufficient, the copper foil is prone to delamination with other materials during the lamination process, resulting in small holes.

2. Poor compatibility with the inner circuit board

If the surface roughness and thermal expansion coefficient of the copper foil and the inner circuit board do not match, internal stress will be generated between the two during the pressing process due to temperature changes and other factors. When the internal stress exceeds the strength limit of the copper foil, it will cause small holes in the copper foil. For example, the thermal expansion coefficient of the inner circuit board is relatively high, and it will shrink during the cooling process after compression, causing pulling force on the copper foil and easily causing it to break.

Article source: Internet