Overview of PP films commonly used in PCB

one. Introduction

In the field of electronic manufacturing, printed circuit boards (PCBs) are a key component of electronic products. In the PCB manufacturing process, PP film (Prepreg, semi-cured film) plays a vital role. It is an indispensable material in the pressing process of multi-layer PCB boards, and it has a profound impact on the performance, quality, reliability, etc. of PCB boards. The correct understanding and selection of suitable PP film is essential to produce high-quality PCB boards that meet the needs of different applications. This article will give a comprehensive overview of the PP curing sheets commonly used in PCB, including their definition, common models, characteristics, and selection principles.

two. What is PP film?

PP film is a glass fiber reinforced epoxy resin semi-cured film. In the uncured state, it has a certain viscosity and softness, and can be easily operated and laminated. In the PCB pressing process, when the temperature rises to a certain extent and a certain pressure is applied, the epoxy resin in the PP film will undergo a curing reaction, thereby firmly bonding the multilayer PCB board together to form a whole.

The main components of PP film include epoxy resin, curing agent, glass fiber cloth, etc. Among them, epoxy resin provides good adhesion properties and electrical insulation properties; curing agent is used to initiate the curing reaction of epoxy resin; glass fiber cloth plays an enhanced role, improving the mechanical strength and dimensional stability of PP film.

three. Common models of PP film commonly used in PCB

1、Model 106 PP

Model 106 PP film is a more common type. Its glass fiber cloth is relatively thin and usually has a lower thickness. This makes it widely used in some occasions where PCB board thickness requirements are more stringent, such as small electronic equipment and high-density PCB design. Type 106 PP film can provide good electrical insulation properties after curing, and has little impact on the transmission of high-frequency signals. Its fluidity is moderate, and the gap between the PCB boards can be evenly filled during the pressing process to ensure good bonding effect. Generally used in the manufacture of HDI boards and multi-layer ultra-thin PCB circuits.

2、Model 1080 PP

Type 1080 PP film is very commonly used in PCB manufacturing. Its glass fiber cloth has a moderate thickness, which can achieve a good balance between mechanical strength and processing performance. This type of PP film has good adhesion, whether it is combined with copper foil or other layers of PCB material, it can ensure a reliable connection. In terms of electrical performance, 1080 can provide stable insulation performance and effectively prevent short circuits and leakage between circuits. Moreover, its thermal stability is good, and its structure and performance can be maintained stable when the PCB board undergoes a high temperature environment. 1080 PP chips are widely used, such as multi-layer PCB, HDI board, high-frequency PCB, high-speed PCB, etc.

3、Model 2313 PP

Type 2313 PP film has some unique characteristics. Its glass fiber cloth braided structure is relatively special, which makes it advantageous in certain PCB designs. This type of PP film exhibits high fluidity during the pressing process, which can better fill the gaps between the PCB layers of complex shapes and ensure close integration between layers. In terms of electrical insulation properties, 2313 can meet the requirements of most conventional circuits. At the same time, it also has excellent performance in heat resistance. It is suitable for some PCB application scenarios that need to withstand higher temperatures, such as automotive electronics, industrial control and other fields. 2313 is a kind of PP film that is not commonly used, except in special cases, it is generally rarely used.

4、Model 2116 PP

The glass fiber cloth of type 2116 PP film is relatively thick, which gives it high mechanical strength. In some occasions where the mechanical properties of PCB boards are required to be high, such as equipment that needs to withstand large external forces, vibration or shock, type 2116 PP film is an ideal choice. Its adhesion after curing is also very strong, which can ensure that the PCB board will not be layered in a complex use environment. From the perspective of electrical performance, 2116 can provide reliable insulation properties and maintain good signal transmission characteristics in high-frequency circuits. 2116 PP is also widely used, and it is commonly used in multi-layer PCB, high-frequency PCB, high-speed PCB and other products.

5、Model 1506 PP

Type 1506 PP film has a moderate thickness and good processing performance. While its glass fiber cloth guarantees a certain mechanical strength, it makes this PP film easier to operate during the pressing process. In terms of electrical insulation properties, 1506 can meet the design requirements of general PCB boards, and its dimensional stability after curing is good, which can ensure that the PCB board will not have problems due to dimensional changes during processing and use. This type of PP film is widely used in the PCB manufacturing of some low-end electronic products.1506 PP is also a kind of PP film that is not commonly used, unless under certain circumstances, general manufacturers rarely use this type of PP film.

6、Model 7628 PP

Type 7628 PP film is a thicker type of glass fiber cloth. It has very high mechanical strength and is suitable for manufacturing PCB boards that need to withstand extreme mechanical stress, such as in aerospace, military equipment and other fields. Although its glass fiber cloth is thicker, it can still ensure good bonding effect under the appropriate pressing process. In terms of electrical properties, 7628 can also provide reliable insulation properties, but due to its thick glass fiber cloth, its application in high-frequency circuits may be limited.Compared with 1080 and 2116, 7628 PP film has relatively few uses, and is generally used in the fields of multi-layer PCB, high-frequency PCB, and mixed pressure plate with special requirements.

Four, the characteristics of PP curing sheet

1. Electrical insulation properties

Good electrical insulation performance is one of the key characteristics of PCB film. This ensures isolation between the circuits and prevents current leakage and short circuit phenomena. Different types of PP film may have different electrical insulation properties, which mainly depends on the composition of its epoxy resin, the structure of the glass fiber cloth, and the degree of curing and other factors. In the design of high-frequency circuits, PP films that have little influence on high-frequency signals and have a stable dielectric constant need to be selected to ensure accurate signal transmission.

2. Mechanical strength

Mechanical strength is essential for PCB boards to withstand external forces, vibration and shock during use. The glass fiber cloth in PP film provides the main mechanical strength, and the glass fiber cloth of different thicknesses and braided structures determines the mechanical strength characteristics of different types of PP film. Thicker glass fiber fabrics usually provide higher mechanical strength, but may bring some challenges in terms of processing performance and electrical performance.

3. Thermal stability

In the manufacturing process and actual use of PCB boards, different degrees of high temperature environments may be experienced. PP film needs to have good thermal stability to ensure that it will not soften, deform or decompose at high temperatures. PP film with good thermal stability can ensure the reliability and service life of PCB boards in high temperature environments.

4. Liquidity

In the PCB board pressing process, the fluidity of PP film is an important characteristic. PP film with good fluidity can better fill the gaps between the PCB board layers and ensure close integration between layers. However, excessive fluidity may cause problems such as resin overflow, which affects the appearance and quality of the PCB board. Therefore, it is necessary to select PP film with suitable fluidity according to the design and pressing process of the PCB board.

5. Dimensional stability

Dimensional stability refers to the ability of PCB film to maintain its size unchanged under different environmental conditions (such as temperature and humidity changes). PP film with good dimensional stability can ensure that the PCB board will not have installation problems or electrical performance degradation due to changes in size during processing and use.

five. Parameters of commonly used PP curing tablets

In the field of electronic manufacturing, the quality of PCB is directly related to the performance and reliability of electronic products. PP curing sheet is one of the key materials for manufacturing multilayer PCB boards. The parameters of PP film, such as glue content, thickness, DK value, DF value, resin flow, glassy transition temperature, etc., have a decisive impact on the performance of PCB boards. Let's take Shengyi S1000H as an example to take a look at the common parameters announced by the manufacturer.

six. How to choose PP film?

1. According to the design requirements of the PCB board

If the PCB board design requires higher mechanical strength, such as in some industrial equipment, automotive electronics and other fields, then you can choose a thicker glass fiber cloth model, such as 2116 or 7628. For those PCB boards that need to work in a high-frequency environment, priority should be given to PP films that have a small impact on the high-frequency signal and have a stable dielectric constant, such as models such as 106. If the design of the PCB board has strict thickness restrictions, then a thinner model such as 106 or 1506 may be a more suitable choice.

2. Consider the requirements of the manufacturing process

In the manufacturing process of PCB boards, different manufacturing processes have different requirements for the characteristics of PP film. For example, if the temperature and pressure of the pressing process are high, then it is necessary to choose PP film with good thermal stability to avoid problems during the pressing process. If the PCB board has a large number of layers, then you need to choose PP film with good fluidity to ensure that the layers can be closely combined.

3. Meet the needs of the use environment

For those PCB boards used in harsh environments such as high temperature, high humidity, and high vibration, PP film with corresponding characteristics needs to be selected. For example, for PCB boards used in high temperature environments, models with good thermal stability should be selected; for PCB boards used in high vibration environments, models with high mechanical strength should be selected.

4. Comprehensive cost factors

When choosing PP film, in addition to considering performance and quality requirements, cost factors also need to be considered. The price of different types of PP film may vary, and in the process of use, the processing costs of different types may also vary. Therefore, it is necessary to consider the factors of performance, quality and cost comprehensively, and choose the most suitable PP film to achieve the best price/performance ratio.

In short, PP film plays a vital role in the manufacturing process of PCB boards. Through an in-depth understanding of the characteristics and selection principles of different types of PP film, it can help PCB manufacturers produce high-quality PCB boards that meet the needs of different applications.