New-Tech Europe Magazine | Q1 2023

Credit: Samtec

Class 3, or “High Performance/Harsh Environment Electronic Products,” refers to high-reliability products where performance is cri t ical . Examples include military, aerospace, and medical applications. If these solder joints fail a person might be injured or even killed. A significant number of Samtec connectors are rated IPC Class 3. An IPC Class 3 rating doesn’t mean every time an EOEM solders a connector they achieve a Class 3 solder joint. Other factors come into play, such as stencil thickness, the precision of the connector placement, and pad design, to name a few. The illustration above shows the difference between a Class 2 vs. Class 3 solder joint. Dimension W is the width of the component lead, and dimension A is how much of the lead is extending over the solder joint/PCB pad. For Class 2 solder joints, A can be one-half of W. In other words, 50% of the lead can be “off” of the side of the pad. For a Class 3 joint, A can only be 25% of the width of W. This is just one quick example that illustrates the differences between Class 2 and Class 3 solder joints. Here’s a link to learn more about the differences between Class 2 vs. Class 3 solder joints. Do I need to do anything special if I am conformally coating my PCBA? Conformal coating is a common

or more I/Os on a single connector. If an internal solder joint on an array connector has a problem – and the vast majority of solder joints on an array connector are internal/under the insulator – your only recourse is to remove that connector and replace it with a new one. Simply described, the process involves placing the PCB into a hot air rework station. A nozzle is placed on the top of the PCB, just above the surface, but surrounding the connector. A prescribed thermal profile is executed where hot air is introduced around the array connector, the solder melts, the nozzle is lifted off the PCB, and the connector is literally removed from the board using pliers or tweezers. The board will need to be cleaned and the old solder removed. Our Air Vac rework system blows hot air on the solder to keep it molten, and a nozzle removes the solder. Once the solder is removed, the rest of the PCB is cleaned. Then, using a mini-stencil, fresh solder paste is printed on that PCB. A new connector is placed on the PCB, the hot air nozzle is placed over the connector, and a profile is run to resolder the new connector. Although it sounds complex, this process works very well. Samtec recommends maintaining an approximately 1/8” (3.175 mm) “keep out area” around the connector to leave room for this rework system, on the slim chance it’s needed.

pract ice. One of the biggest challenges in preparing a PCB for conformal coating is to protect the contact surfaces, which are typically internal to a socket strip connector, but not always. Also of concern are exposed terminal strip pins for an unshrouded connector. Masking becomes important in these applications. Here’s a link to a document that discusses several of the more commonly used methods of applying conformal coating as well as masking methods. Parylene conformal coat ing is popular. This is a complex process that requires significant masking. The Parylene process involves taking the PCB assembly and placing it into a chamber where a vacuum is pulled. As the vacuum is pulled, the Parylene coating is introduced into the chamber and it goes everywhere air can go, allowing the Parylene to get into every nook and cranny of the connector(s). As you can imagine, it’s very difficult to mask all of the critical areas. If a customer asks us about the Parylene process, we refer them back to the Parylene manufacturer. If there is a solder joint problem with an array connector, how do I rework it? As the name implies, array connectors are larger and they typically have an X, Y grid of positions. Samtec grid array connectors frequently have 500

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