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Summary/Introduction
Plating affects the longevity and quality of a connector system, including corrosion resistance, conductivity, solderability, and of course, cost.
【Background of the Classroom】
This is the third part of a series on issues related to connector plating from Samtec's Phil Eckert, Quality Engineering Manager, and Matt Brown, Principal Engineer, on "Primer Plating, Substrate Metal, Lubrication, Voltage."
Previous series have received unanimous recognition and good feedback. That's why the third part of the series is now available to answer your questions about connector plating.
These issues mainly relate to gold and tin plating, as this is the most common plating option for connectors.
Q1: What plating is best? What should be the thickness of the priming plating?
A1: Samtec priming has a minimum nickel content of 50 μ". This not only improves durability but also prevents substrate metal migration. Nickel base plating creates a physical barrier between the copper and gold surface treatment or plating of the pins. The price of nickel is also cheap.
The disadvantage of nickel is poor ductility. If the connector leads are formed or bent after plating (as in the right-angle molding process), too thick plating can cause cracking.
Q2: Do you recommend lubricating the connectors?
A2: We rarely recommend lubricating Samtec connectors as it is not necessary for most of our customers' applications. Still, we are not averse to lubricating connectors, and you can use lubricant on our connectors.
For example, some of our connector series have unusually high normal forces, mating and mating forces, so we offer standard lubrication options for these connectors. In these cases, the connector may be damaged during mating and unplugging, possibly due to excessive normal force.
In addition, lubrication adds an extra layer of corrosion protection. We have successfully used lubricants on both gold-plated and tin-plated contacts. Lubricants were initially widely used for tin-to-tin bonding. This bond can lead to fretting corrosion, which can be easily mitigated by lubricants. Gold-on-gold bonding can use lubricants to seal pores and extend service life in corrosive service environments.
Q3: What is the rated voltage and current amperage of the connector gold and tin plating?
A3: In the previous Q&A session, we mentioned that the maximum continuous service temperature for tin plating is 105°C and the maximum continuous service temperature for gold plating is 125°C. While we have connectors designed specifically for power applications, most Samtec board-to-board components are signal-transmitting, with current levels ranging from around 5.00 amps for a 5.00mm pitch dual-blade "power connector kit," to 5-6 amps for a 2.54mm pitch connector kit, to around 0.80 amps for a 2mm pitch microsystem.
The amount of current that a contact system can carry is best expressed in terms of current carrying capacity (CCC). The geometry of the contact system, environmental conditions, and the density and location of components on the customer's printed circuit board all affect the inevitable natural temperature rise as current passes through the connector. Our goal is to keep the current at a level that does not exceed the maximum continuous use temperature. Therefore, the amount of current that the connector system can withstand is temperature-dependent.
Q4: Does the base metal affect the function of gold or tin plating?
A4: We do not recommend surface treatment based on the base metal of the connector pins. At Samtec, most of our terminals and contacts are made of phosphor bronze or beryllium copper, and both gold and tin plating work well with both. Gold plating is common on beryllium copper contact systems, often because smaller, higher-density, lower-profile connector systems are typically made of beryllium copper. These smaller contact systems produce lower normal forces, between 30 – 40 grams, so gold-plated beryllium copper is more popular.
Similarly, the insertion and pull-out forces are also a consideration for tinned contact systems. As mentioned in the first part of the series, the minimum thickness of a tinned contact system is typically 100 microinches, typically 150 microinches or more, which can affect the insertion and pull-out forces, especially in high-density (i.e., high-pin-count) connector systems.
Plating combinations with nickel base plating are specifically designed for copper-based alloys.
Q5: What kind of plating should be used for edge card connectors?
A5: We recommend plating hard gold on the pins of the edge card connector; Our gold is cobalt-hardened gold. Similarly, we recommend that the pads on the printed circuit board mated to the connector also use cobalt-hardened gold. For pads, we recommend a hardness of ASTM B 488 Type 2, Grade C. We recommend this because most edge card applications go through high mating cycles.
【Summary】
As a company with decades of experience in the connector industry, Samtec has a solid technical accumulation and diverse practical experience in connector plating. We understand every challenge encountered in the connector design process.
In the future, we will continue to bring the fourth and fifth parts of the connector small class Q&A series, so stay tuned!