A lot of older (ceramic) ICs have a gold-plated line extending from the die cover to the edge of the package. Did this serve a practical purpose or was it just bling?

I suspect that it might be what's left of the lead frame leading to the pad under the soldered die cover. It would hold the pad in position while the package was molded. Similarly, the gold plating on the pin-1 notch in the photo below is part of the trimmed lead frame. This is just a hypothesis; can anyone confirm?

XC68000 DIP package Source: Wikipedia/Arnold Reinhold (CC/A-SA)

up vote 19 down vote accepted

It's a ground wire. The way ICs were manufactured back then had the metal cover placed over the die as the last step, and grounding it helps protect the die from static shock and interference.

If you look closely you can see the solder that bonds the strip to the die cover. If you check continuity you will find that both are connected to the IC's ground plane and ground pin(s).

  • When would it be grounded though? The line doesn't connect to any pin. – Alex Hajnal Nov 19 at 9:27
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    It connects to the exposed ground plane on the side of the IC. – user Nov 19 at 9:29
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    I guess they don't have to be, there is a cost to it so if it wasn't necessary for that particular part they might skip it. It depends how sensitive it is, what the application is, that kind of thing. Manufacturers quickly moved to plastic packages once they became practical. – user Nov 19 at 10:33
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    MBA810 is a high power (up to 10W depending on manufacturer) amplifier. The 'wings' aren't ment as ground (although they are connected), but for cooling. They do not go over the IC (like the cap) but below to transfer heat. – Raffzahn Nov 19 at 15:07
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    Also, the metal cap is never atatched to the die inside, as the upper side of a die contains circuitry and a metal cap will carry a high chance of shortcuting. Heat for dissapation is taken from the lower side. That's why modern CPUs are flip mounted, so heat transfer can be aproved ( also it allows more connections, as now pins may also connect to pads inside the chip, not just aroudn the border. – Raffzahn Nov 19 at 15:13

Definitely not "bling". Since gold is (obviously) expensive, there is only one reason it's used in electrical circuits: it's because it doesn't corrode (oxidize), and therefore it makes for the best interconnects. There are better conductors out there, such as silver (the best), but they all have issues with corrosion to some extent or another. Think of the "tarnish" that quickly builds-up on any silver that gets exposed to oxygen. But you can drop a piece of gold in the ocean and come back a year later and it still won't have any oxidation on it whatsoever.

  • Welcome to Retrocomputing.SE! This doesn’t answer the question, which is specifically about the gold line extending along the top of the IC’s package, not the use of gold in general. – Stephen Kitt Nov 20 at 11:43
  • Thanks. Sorry, I thought my answer was implied. As several people mentioned the connections made to this chip (whether electrical, or for thermal dispersion), gold will always maximize connection quality over the life of a product. – ColdCold Nov 20 at 21:20

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