PCBA Tech - SMT backplane size and weight and the use of glue

Requirements for backplane size and weight in SMT patch processing

The backplane is a professional product in SMT chip processing. The design parameters of the backplane are very different from most other PCB circuit boards. The future backplane is larger and more complex, and requires an unprecedented high Clock frequency and bandwidth range.

The ever-increasing demand of users for increasingly complex large-size backplanes that can work at unprecedented high bandwidths has led to the need for equipment processing capabilities beyond conventional PCB manufacturing lines. In particular, the backplane is larger, heavier, and thicker, and requires more layers and perforations than standard PCBs.

The size and weight of the backplane in SMT chip processing require the conveyor system. Generally, the biggest difference between PCB and backplane lies in the size and weight of the board and the processing of large and heavy raw material substrates. The standard size of PCB manufacturing equipment is typically 24x24 inches. However, users, especially users of special groups, require a larger size of the backplane. This has promoted the approval of large-size board conveying tools and the hope of purchase.

At the same time, developers and designers have to add additional copper layers to solve the wiring problem of the large-pin-count connector, so that the number of backplane layers can be increased to meet customer requirements. At the same time, the harsh EMC and impedance conditions also require an increase in the number of layers in the design to ensure adequate shielding and improve signal integrity.

As user applications bring more and more requirements on the number of board layers, the alignment between layers becomes very important. Interlayer alignment requires tolerance convergence. In SMT chip processing, the board size has changed, and this convergence requirement has reached an unprecedented high. All layout processes are required to be produced in a certain temperature and humidity controlled environment. As users require more and more circuits to be laid in a smaller area in terms of PCB routing, in order to keep the fixed cost of the board unchanged, the size of the etched copper plate is required to be smaller, which requires better alignment of the copper plates between layers .

Glue usage requirements during SMT patch processing

Leaded component through-hole insertion (THT) and surface-mount (SMT) coexistence of the placement and insertion mixed assembly process is currently the most common assembly method used in the production of electronic products. In the entire production process, one side of the printed circuit board (PCB) components are glued and cured at the beginning, and then wave soldering can be carried out at the end. During this period, the interval is longer, and there are many other processes, and the curing of the components It is particularly important, so there are certain requirements for the selection and use of SMT patch processing glue.

1. The choice of glue for SMT patch processing:

The glue used in chip processing is mainly used in the wave soldering process of chip components, SOT, SOIC and other surface mount devices. The purpose of fixing the surface mount components on the PCB with glue is to prevent the components from falling off or shifting under the impact of high-temperature wave crests. Generally, epoxy resin thermal curing glue is used in production, instead of acrylic glue (which requires ultraviolet radiation to cure).

2. Requirements for the use of glue in SMT patch processing:

1. The glue should have the thixotropic properties of the opportunity;

2. No drawing;

3. High wet strength;

4. No bubbles;

5. The curing temperature of the glue is low, and the curing time is short;

6. Have sufficient curing strength;

7. Low hygroscopicity;

8. Has good repair characteristics;

9. Non-toxic;

10. The color is easy to identify, and it is convenient to check the quality of the glue dot;

11. Packaging. The packaging type should be convenient for the use of the equipment.