Is Goldfinger real gold

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Is Goldfinger real gold?

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In the interface part of various expansion modules (memory modules, graphics cards, SSDs, high-speed cables, etc.) of the computer, you can see rows of golden yellow contacts, commonly known as gold fingers.

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The term “gold finger” is often used to describe a row of golden, conductive contacts on a printed circuit board (PCB). These contacts are usually made of metals such as gold or nickel, which have good conductivity and corrosion resistance. In computer hardware, gold fingers are mainly used for the connection between memory modules (such as RAM bars), graphics cards, and other expansion cards and the motherboard, which are responsible for establishing a stable electrical connection.

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“Goldfinger” is derived from the English “Gold Finger”, both of which are very intuitive in their respective contexts and completely independent of cultural influences…… After all, gold is really the consensus of the people of the earth!

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With the gold finger, is the Edge Connector, the corresponding Chinese is the edge (card) connector or card edge connector, that is, various slots.

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Compared to soldering, connectors are easy to use. Electrical connections can be easily formed through gold fingers, PCB-to-PCB (board-to-board), or PCB-to-cable (wire-to-board). However, connectors as moving parts also come at the cost of reliability. In order to connect reliably, the “gold finger” in the connector really uses gold! The general process is to plate nickel on top of the copper foil, and then possibly some intermediate metal plating, and finally gold plating on the surface.

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To put it simply, a serious gold finger is not only resembling it, but it should also be “is” gold.

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Why gold?

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Gold, silver, and copper are all metals known for their good electrical conductivity for electrical connections. As a highly conductive and relatively inexpensive metal, the main conductor in circuit boards is copper foil. But why does the interface part prefer much more expensive gold?

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First of all, because copper is more susceptible to oxidation and corrosion, it is best to be protected from direct contact with air and moisture. For the insulated part, it can be covered by PCB or insulating varnish; For the part that needs to be connected to the outside, other metals can be plated, for example, the pad part can be tin or immersion gold, and the interface part (gold finger) can be plated with gold. Silver also carries the risk of oxidation and corrosion, making it unsuitable for connectors.

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Secondly, gold has excellent toughness and ductility, and has better retention under mechanical force. This is important for interfaces that need to be plugged and unplugged repeatedly. The workmanship and thickness of the gold layer directly affect the reliability and durability of the connector.

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There are two ways to achieve a gold layer on the surface of a circuit board: gold plating and immersion gold.

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According to the good chemical and physical properties of gold, the advantages of interface gold plating summarized in practice by the electronics industry include:

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“Golden” standard

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Due to the high cost of gold, controlling the thickness of the plating directly affects the amount of gold used, which has a huge impact on the cost. Depending on the application, there are a number of criteria to guide how to find a balance between cost and reliability. For example, for M.2 SSDs, the specification formulated by SNIA mentions three layers of plating of different qualities: Gold Flash, 15u”, and 30u”. Of these, 30 u” is 30 microinches (μin), which is about 0.76 micrometers (μm), and 15 u” is 0.38 microns. As for Gold Flash, flash gold refers to the pretreatment procedure before electroplating, which is only initially plated with a layer of gold, which is very thin (even below 0.1 microns), and has not yet formed a dense coating, which may not be able to completely cover the nickel plating layer, and there is a risk of oxidation and corrosion. If the SSD interface is plated with flash gold, it may only be able to cope with a few installations, and there is a possibility of poor contact (corrosion) after a long time, and you dare not expect repeated plugging and unplugging. In short, there may be three different levels of durability in the case of M.2 interfaces, after all, there is no hot-swappable scenario in the design specifications and technical positioning of M.2, so it is acceptable to choose a slightly thinner interface plating when not pursuing maintenance. For low-load consumer electronic products, the use of lower standards is conducive to controlling costs and avoiding waste, but for more demanding occasions, such as enterprise-level and industrial-level scenarios, then the standards will be raised accordingly, and the actual reliability bottom line depends on the brand positioning.

As for the source of “30u”, it is generally believed to be from the IPC-6010 series of standards established by the IPC (Connected Electronics Industries Association). Among them, the IPC-6012 standard is the identification and performance specification of rigid printed boards, which is the category of commonly used computer boards. IPC-6012 divides the surface coating into three grades, and the following table can be referred to for the board edge connector plating:

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The plating on top of the copper foil is first nickel plating, and finally gold is added, possibly using other metals (such as palladium) between nickel and gold. The grade of the plating can be understood to increase according to the total thickness of nickel and gold, where the thickness of the surface layer of gold varies greatly.

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In SNIA’s vision, the quality of the plating of M.2 SSDs may not meet the requirements of IPC-6012 (at least 30 u”), but for data center SSDs, hot swapping is the basic requirement, and the interface is directly mated to the high-speed backplane interface, so the PCB will follow the requirements of IPC-6012, and the gold plating thickness of the interface needs to be at least 30 u.”

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How many times can a 30 U” gold finger withstand plugging and unplugging? It is generally believed that it can reach thousands or thousands of times. Even if you plug and unplug one round trip a day, it will not be 10,000 times of friction in ten years. However, considering the impact of vibration and mechanical shock on the mechanical reliability of the butt insert, it is reasonable to retain a safety margin of two to three orders of magnitude.

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Conclusion

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“Good steel is used on the blade” is a kind of “lean” pursuit, and it is also very appropriate to use it on the gold finger, and choose a reasonable quality according to the actual application needs.

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