What you have to know about HDI

2018-11-23 17:47Writer: qyadminReading:
     Do you still remember IBM Simon? It is the "father" of smart phones. It came out around 1995 and was the most creative electronic product at that time. However, it didn't look like what a smart phone looks at present and it weighed 510g with a thickness of 38mm. Can you believe it? It's totally impossible for you to put it in your pocket.
  With the improvement of functions and people's aesthetic attitude towards cell phones, smart phones have experienced a series of changes in terms of size and figure. Figure 1 indicates the thickness change of smart phones in the past years.

 about HDI

  Besides smart phones, manufacturers of pads and desktops are all striving for miniaturization. All these size reductions depend on the design and use of High Density Interconnect PCBs (HDI PCBs). If you just think HDI PCB is only the Herbalife for smart devices, you are definitely wrong. The function of HDI technology aims to make smart devices lighter, smaller, thinner and more reliable.
  HDI PCBs refer to the print circuit boards with high density, fine lines, small drill diameter and super thinness. This kind of PCB enjoys fast development since its occurrence based on the protruding advantages:
  1. HDI technology can help reduce PCB cost;
  2. HDI technology increases the lines density;
  3. HDI technology is good for the use of advanced packaging;
  4. HDI technology has better electrical performance and signal validity;
  5. HDI technology has better reliability;
  6. HDI technology is better at heat dissipation;
  7. HDI technology is capable of improving RFI (radio frequency interference) / EMI (electromagnetic interference) / ESD (electro-static discharge);
  8. HDI technology increases design efficiency;


  Some new requirements are brought to HDI PCB material including better size stability, antistatic mobility and non-adhesive. The typical material of HDI PCB is RCC (resin coated copper). There're three types of RCC, namely Polyimide metalized film, Pure polyimide film, Cast polyimide film.
  The advantages of RCC include: small thickness, light weight, excellent flexibility and flammability, compatibility with characteristic impedance and excellent size stability. In the process of HDI multi-layer PCBs, taking place of the role of traditional bonding sheet and copper foil as insulating medium and conducting layer, RCC can be suppressed with chip through traditional suppression technology. Then non-mechanical drilling method is used such as laser so that micro-via interconnect can be formed.
  The occurrence and development of RCC push PCB products from SMT (surface mount technology) to CSP (chip scale package), from mechanical drilling to laser drilling, and promote the development and progress of PCB micro-via, all of which results in RCC's leading material of HDI PCBs.
  In the practical PCB manufacturing process, as for the selection of RCC, ordinarily there is FR-4 standard Tg 140C, FR-4 high Tg 170C and FR-4 and Rogers combined lamination, which are now mostly used. With the development of HDI technology, more requirements must be met by the HDI PCB material, so the main trend of HDI PCB material should be with:
  1. The development and application of flex material with no adhesive used;
  2. Small thickness of dielectric layer with small deviation;
  3. The development of LPIC;
  4. Increasingly small dielectric constant;
  5. Increasingly small dielectric loss;
  6. High soldering stability;
  7. Strict compatibility with CTE (coefficient of thermal expansion);

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