PCB Tech - PCBA surface mount design

PCBA surface mount connectors undoubtedly provide many advantages, including reducing assembly costs, providing double the density and improving the integrity of high-speed performance. However, PCBA surface mount connectors also contain some recognized shortcomings-from reliability issues (such as the connector falling off the circuit board) to assembly issues caused by coplanarity. In fact, these so-called cognitive shortcomings will no longer be a problem if the design engineer undergoes thorough and careful consideration and review during the process of selecting the appropriate connector.

Therefore, when you choose a PCBA surface mount connector, you may wish to consider the following points: Which PCBA surface mount pin design is used and the reason for using the design; which measure to use to achieve mechanical stress relief; coplanarity Whether the problem can be solved; whether it is easy to obtain the sample board and test report. When purchasing, you should ask all the above questions and make a decision based on the actual situation, not based on the statement provided by the salesperson. Keep in mind that the design of PCBA surface mount connectors is not exactly the same.

Pin design

After carefully observing the PCBA surface mount pins of the connector you are considering using, you need to ask the connector engineer what methods have been taken to ensure that the solder can remain on the key junctions between the PCBA surface mount pins and the solder pads. In addition, the pins of the connector are vertical, J-shaped, or other types? You may ask the company's sales staff why the connector uses this pin type. If they don’t know the answer, report it to you after they find out the reason, and then consider their product further.

The design elements of PCBA surface mount connectors are not implemented casually. Once the design has been completed, there can be no reliability problems or weak joints. Engineers who design PCBA surface mount connectors select specific design elements based on specific reasons, and it is very important for you as a design engineer to understand the reasons.

Stress relief measures

Even if the design of the signal and power pins is sufficient to increase the integrity of the soldering process, don’t stop your premium on the connector. After all, you don't want all the plugging force to be completely dependent on the adhesion of the signal pins on the PCB board. What must be mentioned is the lateral force caused by the good intentions of the on-site technicians but lack of information. In fact, the mechanical stress on these circuit boards must be very small. However, many connector companies ignore this key detail, resulting in PCBA surface mount connectors not only having a negative reputation in terms of durability, but also in general. /O is not considered for use in applications.

In some cases, a very reliable PCBA surface mount connector can actually compete with through-hole return connectors. For example, PCBA surface mount D-Sub connectors will not fall off the circuit board because their design is not ultra-thin and slim. However, we must actually understand that the stress that a PCBA surface mount D-Sub connector can withstand is limited after all. In some cases, the overall size of the PCBA surface mount connector needs to be the same as that of the through-hole return connector to ensure a reliable connection. For larger stress-relief solder pads that are used daily in harsh environments, the external structure and dimensions need to be similar to those of through-hole reflow connectors. Although the PCB does not provide substantial savings, the PCBA surface mount version can provide dual card density, simplify assembly, and potentially reduce manufacturing costs. In I/O applications, consider using PCBA surface mount connectors. If the design circuit board space is limited, there are many PCBA surface mount connectors for you to choose from.

If the PCBA surface mount connector you are considering does not have accessories that can ensure a reliable PCB connection, it is recommended that you give up choosing this connector. PCBA surface mount connectors must have sturdy mechanical accessories to withstand multiple mating cycles and rough handling. As a design engineer, you respect the choice of connectors, which does not mean that the general assembly personnel will do the same. Please keep in mind that unless PCBA surface mount connectors have design problems, they will never fall off the circuit board. At the same time, you need to carefully and thoroughly evaluate all possible situations that the connector may face after being designed into the system. For example, can PCBA surface mount connectors withstand the daily mating of I/O cables or heavy-duty mezzanine cards? Can they withstand the back-and-forth shaking that may be faced when the connector is unplugged?

Double check the PCBA surface mount connector you are considering. Does the connector have additional solder pads or solder anchors to ensure a reliable connection? Make sure you are satisfied with any additional measures taken by the connector company. Can you truly feel the durability of the connector? Is there a test board for manual operation? Can the supplier provide a test report of the X and Y layer shear data?

All PCBA surface mount connectors must be equipped with some form of strain relief. Some connector companies use screws to lock the circuit board or accessories to the panel to achieve strain relief. Although these concepts may increase mechanical strength, some solutions can even provide the necessary and reliable circuit board support without the need for secondary assembly or manual negotiation.

Through-hole reflow technology enables PCBA surface mount connectors to pass through pick-and-place machines and provides a more robust circuit board connection than PCBA surface mount technology. Similar to through-hole pins, both through-hole reflow soldering or lead immersion solder paste require fine holes to be partially drilled into the PCB so that these thin pins can pass through reflow soldering. These through-hole pins are used in combination with PCBA surface mount signal pins, and often double the load through enhanced mechanical strength and grounding. However, there will be some disadvantages when the through-hole reflow pins are used in high-speed applications.

Although PCBA surface mount pins are used for signal performance, through-hole return pins can provide a more robust connection on the circuit board. Not only that, as the height of the mezzanine connector and the weight of the daughter card continue to increase, the through-hole return pin will undoubtedly provide more outstanding rigidity and strength. Crimping technology has been the de facto standard for backplane connectors for the past 40 years. PCBA surface mount/through-hole reflow backplane solutions often surpass the signal performance of crimping while providing excellent durability. If executed correctly, there is no doubt that PCBA surface mount technology is suitable for any application.