The design of electronic products is becoming more and more modular. Different functional modules can be combined to quickly create high-quality products with different performances. The connection of modules is particularly important. Here is a share shared by a senior hardware engineer. Experience with connector selection.
The connector is just like the function interface of the program. The design is reasonable. In the future, product maintenance, upgrade, and porting will be more effective, making the product lasting vitality. The design is unreasonable, causing difficulties in future maintenance and upgrades. Ultimately, the product is not competitive, and the importance of the connector is self-evident.
A connector, also known as an engineer's connector, is used to connect two boards or electronic devices for power or signal transmission. Through the connector, the circuit can be modularized, simplifying the assembly process of electronic products, and making the product easy to maintain and upgrade.
There are many types of connectors, and common types include communication interface terminals, terminal blocks, wire-to-board connectors, and board-to-board connectors. Each category can be subdivided into several categories, such as:
The board-to-board connector includes a pin header, a PC 104, a board-to-board connector, and the like;
Wire-to-board connectors include FPC connectors, IDC sockets, simple horns, and the like.
For the modular circuit, the selection of the connector plays a decisive role, so from what point of view should we consider the connector suitable for hardware when selecting the connector?
Pin, pitchThe pin count and pin pitch are the basic basis for connector selection. The number of connectors that choose how many pins depends on the number of signals that need to be connected. For some chip connectors, as shown in the following figure, the pin header should not be too many. Because in the soldering process of the placement machine, due to the high temperature, the connector plastic will be thermally deformed, and the middle portion will be raised, resulting in the lead solder joint. In the early days of development, our P800Flash programmer used this type of pin header and busbar to make inter-board connections. As a result, the pins of the prototype pin headers were soldered over a large area. After switching to a pin with two pins that were halved, there was no solder joint.
Nowadays, electronic devices are becoming smaller and more precise, and the pitch of the connectors is also from 2.54 mm to 1.27 mm to 0.5 mm. The smaller the pin pitch, the higher the requirements for the production process. The pitch of the pins should be determined according to the company's production process level. Blind pursuit of small spacing will cause difficulties in production and maintenance.
2. Electrical performanceThe electrical properties of the connector mainly include: limiting current, contact resistance, insulation resistance and electrical strength. When connecting a high-power power supply, pay attention to the limit current of the connector; when transmitting high-frequency signals such as LVDS, PCIe, etc., pay attention to the contact resistance. The connector should have a low and constant contact resistance, typically tens of mΩ to hundreds of mΩ.
3. Environmental performanceThe environmental performance of the connector mainly includes: temperature resistance, moisture resistance, salt spray resistance, vibration, impact and the like. Choose according to the specific application environment. If the application environment is relatively humid, the requirements for moisture and salt spray resistance of the connector are high, and the metal contacts of the connector are prevented from being rusted. In the field of industrial control, the requirements for the vibration and shock resistance of the connector are high, so as to prevent the connector from falling off during the vibration process.
4. Mechanical propertiesThe mechanical properties of the connector include the insertion and extraction force, mechanical foolproofing, and the like. Mechanical foolproof is very important to the connector. Once inserted, it is likely to cause irreversible damage to the circuit!
The insertion force is divided into insertion force and separation force. The maximum insertion force and the minimum separation force are specified in the relevant standards. From the point of view of use, the insertion force is small and the separation force is large. Too small separation force will reduce the reliability of contact. However, for connectors that often need to be plugged and unplugged, excessive separation force will increase the difficulty of pulling out and reduce the mechanical life.
Take our P800Flash programmer as an example. In the previous development process, the horn connector shown in the figure below was used as the connector between the programmer and the adapter board. This connector is tightly contacted and low in cost. The disadvantage is that the mechanical defense is not obvious and the separation force is too large. In the process of replacing the programmer adapter board, tools such as tweezers can be used to separate the pair of connectors, which affects the user experience.
In order to solve the problem of excessive separation force of the connector, we designed a complex auxiliary puller to increase the cost, but the pull-out effect is not obvious.
Then we designed a sheet metal cover to fix the adapter plate to the cover and separate the connector by pulling the cover. The actual test results are not ideal, and even the plastic edge of the connector is cracked and the stitches are skewed.
In order to reduce the connector separation force and facilitate the user to insert and remove the adapter board, we made a lot of attempts, finally found a bright light on the road of exploration, and finally selected the connector shown below, and modified the PCB and products. Shell structure.
The actual test shows that the connector has a unique directivity due to the unique directivity of the slot, and the insertion force is small, the separation force is moderate, and the insertion and removal feel is good, which greatly improves the convenience of use of the plug.
"Details determine success or failure", it is the inconspicuous details of the connector, which determines whether the product has a good user experience, whether it can maintain sufficient competitiveness, remember not to be free!
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