PCB Technical - Impedance board, it is very important to choose a good PCB board factory

One: Engineering data processing.
For manufacturers who really do multilayer boards, as a customer, 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 value requirements. The board will be based on the parameters of your own factory. It's very ok to help you.
1. The material parameters of each factory are somewhat different.
2. The circuit compensation of each factory, the potion of etching and electroplating are different.
3. The inspection standards of each factory are different.
The above three points are destined, it is more reliable if you hand over the impedance to the PCB board factory for deployment! Regarding this point, some sample factories ask customers to adjust the impedance and do it directly off the assembly line. This is completely irresponsible. This may be no problem for single-ended impedance and individual differential impedance, but for multiple sets of impedances such as DDR. Say, it's not reliable at all!

Two: Line accuracy error control.
The line accuracy is not well controlled, and the impedance deviation is the most common problem in many factories! To control the line accuracy, two points must be met:
1. Good line exposure machine. At present, powerful PCB manufacturers use LDI exposure machines. A good LDI exposure machine, more than 2 million. This is a threshold for small factories and low-end board factories.
2. Vacuum etching machine. The precise alignment of the circuit exposure is not enough, and when the sulfuric acid solution is needed for etching, the circuit is fully and accurately etched. This requires a vacuum etching machine to meet, especially for some 3-4mil lines. However, the vacuum etching machine has one characteristic while satisfying precise and full etching: the etching efficiency is slow. Low production capacity! This is taboo by conventional Allegro factories!

Three: pressing.
Press-fitting is very important for impedance boards, especially high multilayer impedance boards! Because the PP dielectric layer will show a state of glue flow under high temperature pressing, at this time, the temperature, process, and calibration control of the pressing are very important! Otherwise, the thickness deviation of the finished dielectric layer will seriously affect the accuracy of the impedance value! Therefore, to determine whether a board manufacturer can make impedance boards, we must pay more attention to whether they have their own pressing equipment! (The whole set of pressing equipment starts at 3 million yuan, and the maintenance cost is expensive)

Four: The technological process is special.
For example, for a 4-layer impedance board, many customers often tell me that a certain Allegro factory can make it in 4-5 days. Why do you need 6-7 days? There is actually a process problem involved here. Many Allegro factories use multiple different orders to combine their production lines, and their impedance boards are not produced under production control. Customers need to adjust the impedance according to their laminated structure. Directly produced, such an impedance board does save time, but the impedance value is not guaranteed at all.
But when we specialize in multi-layer board factories, when dealing with impedance boards, we use a single board to roll off the line. That is to say, even if you have a sample board, we all configure the impedance separately, down to the production line, and then finish the line and then test the line. Tolerance accuracy. In this way, the time must be much slower, but the impedance value is definitely guaranteed. Therefore, the positioning of different manufacturers is different, and the products they make are also different.
There are also some thick copper plates,HDI plates, half-hole plates, and plate-in-the-hole plates, which will cause different delivery times due to different processes.