How to choose solder paste for high-density interconnect substrate (HDI)
1. What is HDI? What is the difference between HDI and non HDI PCB?
As technology develops, the demand for packing more functions into smaller packages is also growing. PCBs designed using high-density interconnect (HDI) technology tend to be smaller and have higher wiring density than traditional PCBs. In addition to thinner spaces, smaller vias, and higher connection pad density, these boards have many advantages over typical prototype boards. Because more components are packaged in a smaller space. HDI PCBs use blind vias, buried vias and microvias, through-holes in pads, and very fine traces to pack more components into a smaller area.
Solder paste is an important material in PCB-PCBA, affecting the quality of PCB component welding. Its printing properties are key factors, including viscosity, fluidity, residence time, and metal content.
2. What is the effect of choosing the right solder paste on the welding of high-density interconnect substrates?
(1). Composition of solder paste: Solder paste is mainly composed of metal powder (tin-based) and flux. For HDI substrates, fine-grained metal powders (such as Type 4 or finer powders) are recommended as they provide better printing resolution and less risk of bridging. In addition, lead-free solder paste has become the standard choice for many high-end applications due to its environmental friendliness and excellent melting characteristics.
(2). Viscosity and printing performance: The viscosity of solder paste is critical to its performance during the printing process. High-density interconnect substrates require solder paste with excellent printing performance to ensure that the solder paste can be accurately printed on tiny pads without overflow or tilting. Selecting a solder paste with moderate viscosity can avoid voids or bridges during printing.
(3). Melting and wetting properties: When selecting solder paste, its melting temperature and wetting properties should also be considered. HDI substrates usually contain multiple layers of delicate circuits, requiring solder paste to melt quickly at a lower temperature and evenly wet each solder joint to reduce the impact of thermal stress on the board. Excellent wetting properties ensure that the solder joint can quickly form a good metal connection after melting, improving the mechanical strength and electrical stability of welding.
(4). Cleaning agent and residue control: Due to the complexity and density of HDI substrates, post-soldering cleaning can be very difficult. Therefore, it is particularly important to select a high-reliability cleaning agent-free solder paste that has extremely low residual corrosiveness after curing and has minimal impact on electrical performance. It can also simplify the production process and reduce cleaning costs.
(5). Compatibility: Finally, the selection of solder paste should also take into account compatibility with substrate materials. Due to the diversity of HDI substrate materials, solder paste needs to be compatible with substrate materials and other assembly materials such as surface mount adhesives to ensure that chemical reactions do not occur during the entire production process. Reliability issues caused by reliability.
Selecting the right solder paste is critical for the welding of high-density interconnect substrates. By considering the above key factors, the welding quality can be significantly improved, thereby ensuring the performance and reliability of the final product. As electronic products move towards higher density and higher performance, the selection of welding materials will also become more professional and rigorous. Therefore, continuous research and development and optimization of solder paste performance will be the key to the future development of the electronics manufacturing industry.
