In a broad sense, packaging is to combine abstract data and functions to form an organic whole. Generally, ceramics, plastics, metals and other materials are used to seal, place, fix, protect and enhance the electrothermal performance of semiconductor integrated circuits. Through the chip The connection points on the upper part are connected to the pins of the package shell with wires, so as to realize the connection with other circuits through the PCB; an important indicator to measure the advanced technology of a chip package is the ratio of the chip area to the package area, the closer the ratio is to 1, the more good. So what are the precautions for making PCB packaging?

Precautions for pcb packaging

I believe that people who have done hardware design have experienced doing Component or Module packaging by themselves, but it is not very easy to do packaging well. I believe everyone has such experience:

(1) The drawn package pin pitch is too large or too small to cause assembly;

(2) The package drawing is reversed, causing the Component or Module to be installed on the back to correspond to the schematic pins;

(3) The large and small pins of the package drawn are reversed, which causes the component to be turned upside down;

(4) The package of the painting is inconsistent with the Component or Module purchased, and it cannot be assembled;

(5) The encapsulation frame of the painting is too large or too small, which makes people feel uncomfortable.

(6) The painted package frame is misaligned with the actual situation, especially some of the mounting holes are not placed in the right position, which makes it impossible to install the screws. And so on, I believe that many people have encountered this kind of situation. I made this mistake recently, so I wrote a special article today to be vigilant, a lesson from the past, and a guide for the future. I hope that I will not make this kind of mistake again in the future.

After drawing the schematic diagram, the package is assigned to the components. It is recommended to use the package in the system package library or the company package library, because these packages have been verified by predecessors. If you can do it yourself, don’t do it yourself. . But many times we still have to do the encapsulation by ourselves, or should I pay attention to what issues should I pay attention to when doing encapsulation? First of all, we must have the package size of the Component or Module at hand. This general datasheet will have instructions. Some components have suggested packages in the datasheet. This is that we should design the package according to the recommendations in the datasheet; if only given in the datasheet The outline size, then the package is 0.5mm-1.0mm larger than the outline size. If space permits, it is recommended to add an outline or frame to the Component or Module when encapsulating; if the space is really not allowed, you can choose to only add an outline or frame to part of the original. There are also some international standards for packaging at the original price. You can refer to IPC-SM-782A, IPC-7351 and other related materials.

After you draw a package, please look at the following questions for comparison. If you have done all the following questions, then there should be no problems with the package you built!

(1) Is the lead pitch correct? If the answer is no, you may not even be able to solder!

(2) Is the pad design reasonable enough? If the pad is too large or too small, it is not conducive to soldering!

(3) Is the package you designed from the perspective of Top View? When designing the package, it is best to design from the perspective of Top View, which is the angle when the component pins are viewed from behind. If the package is not designed at a Top View angle, after the board is completed, you may have to solder the components with four pins facing the sky (SMD components can only be soldered with four pins facing the sky) or on the back of the board (PTH components need to be soldered to the back).

(4) Is the relative position of Pin 1 and Pin N correct? If it is wrong, it may be necessary to install the components in reverse, and it is very likely that the flying lead or the board will be scrapped.

(5) If mounting holes are required on the package, are the relative positions of the mounting holes of the package correct? If the relative position is incorrect, it can’t be fixed, especially for some boards with Module. Since there are mounting holes on the Module, there are also mounting holes on the board. The relative positions of the two are different. After the board comes out, the two cannot be connected well. For the more troublesome Module, it is recommended to let ME make the module frame and mounting hole position before designing the module package.

(6) Did you mark Pin 1? This is conducive to later assembly and debugging.

(7) Have you designed outlines or frames for Component or Module? This is conducive to later assembly and debugging.

(8) For ICs with many and dense pins, have you marked the 5X and 10X pins? This is conducive to later debugging.

(9) Are the sizes of the various marks and outlines you designed reasonable? If it is unreasonable, the design of the board can make people feel that it is not perfect.