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How to solve the problem of warping of double-sided FR-4 copper clad laminate substrate

ZTELEC Insulation Materials | 18-11-15

With the rapid development of the Internet age, electronic products have become a necessity for people’s daily lives, and therefore promote the development of the pcb industry. But the basis for the development of pcb is the improvement of copper clad laminates. However, in the production of double-sided FR-4 copper clad laminates, the problem of substrate warpage often occurs. If you don’t solve this problem, it will increase the cost of the product.

How to solve the problem of warping of double-sided FR-4 CCL laminate substrate?

1. Start with the resin formula

The use of a relatively long molecular chain, relatively good flexibility and curing agent, which is an important means to overcome substrate warpage. FR4 CCL has effectively solved the problem of substrate warpage since the use of tung oil modified phenolic resin.

2. Carefully select the substrate

In the practice of double-sided FR-4 copper clad layer production, we found that the same glue, the same production conditions, using different factory-produced FR-4 to produce copper clad laminates, using some of the factory’s FR-4 made a single The face-to-face copper-clad competition changed from positive to negative. Fiberglass cloth-based single-sided copper clad laminates We have not found that the copper clad laminates produced by different manufacturers’ substrates will change from anti-warping to positive warping, but the copper clads produced by different manufacturers’ fiberglass fabrics have obvious differences in warpage.

3. Strictly control the technical parameters of each production link

In the production process of FR4 copper clad laminates, the technical parameters of each production process are strictly controlled to ensure the consistency of resin content, fluidity and gelation time of the prepreg, which is a necessary measure to improve the flatness of the copper clad laminate.

4. Tension control

When the epoxy glass fiber cloth is glued, the tension of the glue machine should be small and not large. The latitude and longitude of the stacking materials should not be crossed. Do not mix the cloths of different manufacturers. Do not mix the different specifications of the cloth. Different glue machines should be used. It is best not to mix the prepregs produced by different manufacturers.

5. Temperature control

When the product is hot press formed, if the heat transfer oil is used for heating, the temperature difference between the hot press plates is smaller than that of the steam. The heating rate should be moderate, not too slow, and should not be too fast. Pay attention to the fluidity and gelation time of the prepreg, and adjust the amount and thickness of the laminate product to minimize the amount of glue.

6. Laminated menu rational design

Proper design of the preheating temperature and temperature rise rate during the lamination process is a key point for pressing the plate and reducing warpage. The amount of paper and the degree of softness of the paper are also very large and must be applied flexibly.

7. Slow cooling rate

In the hot press forming of double-sided copper clad laminates, it is found that the outer layer of each BOOK has a greater warpage than the inner layer, which is related to the lowering rate of the outer layer than the inner layer. After the end of the hot-pressing and heat-curing stage, some CCL plants adopt a staged cooling and cooling production process, that is, first use warm water or warm oil (for the heat-conducting oil heating system) to cool the first stage of the product, and then use cold water or cold. The oil cools down.

8. Reduce molding pressure

Try to use vacuum press hot pressing, the higher the vacuum, because the low molecular weight is easier to discharge, the lower pressure can make the insulation materials reach higher density, the lower the pressure, the lower the internal stress of the product, so the low pressure molding is adopted. Helps reduce product warpage. Low pressure molding, reducing flow glue is one of the important means to improve the flatness of the copper clad plate and reduce the white corner.

9. Packaging and storage

FR-4 fiberglass cloth should be sealed when stored. Many CCL factories have adopted moisture-proof sealed packaging, which is beneficial to reduce the warpage of the substrate storage process. When the substrate is stored, it should be laid flat. It should not be placed vertically, and it is not suitable to press heavy objects upwards.

10.PCB circuit graphic design balance

PCB circuit graphic design cannot be very balanced. If large-area conductive patterns are encountered, they should be meshed as much as possible to reduce stress.

11. PCB before the process

Before the substrate is put into use, it is best to dry the board (bake at a temperature near the substrate TG for several hours) to relax the substrate stress and reduce the warpage of the substrate during the PCB process. Lower processing temperatures are used in the PCB process to reduce strong thermal shock.

12. Processing direction consistency

The direction of the trademark characters on the CCL substrate indicates the direction of force applied during the processing of the product, commonly known as portrait. In the PCB process, the direction of the lines in the line pattern should be as close as possible to the longitudinal direction of the substrate to reduce stress and reduce warpage of the product. When making multi-layer boards, care should be taken to make the prepreg longitudinally aligned with the longitudinal direction of each layer of PCB.

ZTELEC introduces international advanced production lines and produces high quality double-sided FR-4 CCL laminates in strict accordance with international standards.

Ztelec Group