To make a long story short, it’s not easy to make a good impedance board!
Some model factories give several fixed laminated structures, and then let customers calculate their impedance according to their lamination … To be honest, Xiaobian really wants to swear at these board factories! If you can’t do it, you can’t! How to fool people, but also fool so well!
To make a good impedance board, you must make the following three basic points:
1. Engineering data processing.
For manufacturers who really make multilayer boards, as customers, you don’t need to calculate the impedance yourself. You only need to mark the single-ended and differential lines that need to control the impedance, and put forward the impedance requirements. The board factory will help you calculate it very well according to the parameters of its own factory.
1. The material parameters of each factory are somewhat different.
2. The circuit compensation, etching and electroplating potions of each factory are different.
3. The inspection standards of each factory are different.
The above three points are doomed. It is more reliable for you to give the impedance to PCB factory for allocation! For this, some sample factories ask customers to adjust their impedance and do it directly offline, which is completely irresponsible. For single-ended impedance, individual differential impedance may be fine, but for DDR and other groups of impedance, it is not reliable at all!
Second, line accuracy error control.
Poor line precision control and impedance deviation are the most common problems in many factories! To control the line accuracy, two points must be met:
1. A good line exposure machine. At present, powerful PCB manufacturers use LDI exposure machine. Good LDI exposure machine, one for more than 2 million yuan. This is a threshold for a small factory and a low-end board factory.
2. Vacuum etching machine. Accurate exposure and alignment of the circuit is not enough, and it is necessary to etch the circuit fully and accurately when etching with sulfuric acid solution. This needs vacuum etching machine, especially for some 3-4mil lines. However, vacuum etching machine has a characteristic of low etching efficiency, while satisfying the requirements of accurate and sufficient etching. Low production capacity! This is taboo for the conventional Allegro factory!
Three: pressing.
It is very important to laminate impedance board, especially high multilayer impedance board! Because PP dielectric layer will be in the state of flowing glue under high temperature pressing, at this time, it is very important to control the pressing temperature, process and calibration! Otherwise, the thickness deviation of the finished dielectric layer will seriously affect the accuracy of impedance value! Therefore, to judge whether a board factory can make a good impedance board, we should pay more attention to whether they have their own pressing equipment! (A complete set of pressing equipment starts at 3 million yuan, and the maintenance cost is expensive)
In addition to the above points, this small series also suggests that customers and friends can request to attach impedance report when placing an order to make a board. This cost a little more, but it’s more guaranteed for impedance control. It’s still worth it!
All right! Xiaobian will share so much with you today! I wish you all the best in making boards, thank you!