[sdiy] Silver series TL074/84 op amps

[rsdio at audiobanshee.com]

On Mar 20, 2016, at 12:53 AM, Gordonjcp <gordonjcp at gjcp.net> wrote:
> On Sat, Mar 19, 2016 at 03:08:23PM -0700, rsdio at audiobanshee.com wrote:
>> Over the years, I've seen countless authentic, unadulterated, functional pieces of audio gear with DIP chips that are silver instead of black. I believe that the only way you're going to get to the bottom of this is to collect date codes and manufacturers from authentic chips and then seek out the vintage data sheets for those chips. There should be some official documentation of the chip markings, including the color.
> 
> I wonder if it's down to opacity?  I know that epoxy isn't *totally* light tight, particularly to IR.

Are you suggesting that the silver paint protects the semiconductor(s) from interference? That seems possible, given the many other strange things that have happened to integrated circuits over the years (gamma rays filtered by cellophane).

My theory is that automated assembly by robots (pick-and-place) was just getting started, and this paint allowed for video inspection, orientation, and possibly ensured that the right part was being placed. I know that modern surface mount processes mean that data sheets these days have all sorts of details on orientation, markings, etc., so it seems like earlier decades would have had their tricks and trends for parts inspection. There's gotta be a clue in an old data sheet, unless some manufacturer is reading this list and can explain it.

Brian