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I have noticed that occasionally some USB mini-B connectors have what looks like a transparent yellow tape on their top.

It might be Kapton tape, but I am not sure.

As an example, please see the below image:

Adafruit 284

(source)

Usually, I leave this tape on. I am wondering, does anyone know what this yellow tape is for?

All I can think of is for protection during soldering, but I am not sure if that's applicable for machine-soldered circuits.

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    \$\begingroup\$ kapton is standard tape for wave soldering and IR. here the flat surface allows suction pick and place \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Aug 18 at 21:47
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    \$\begingroup\$ @tlfong01, Du Pont invented Kapton and commercialized Cellophane, but 3M probably invented the adhesive that makes the tape sticky. (confirmed here) \$\endgroup\$ – The Photon Aug 19 at 6:20
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    \$\begingroup\$ @tlfong01 Kapton tape itself is smooth and mostly none vacuum penetrable. So by gluing it to a rough/open object, it provides a way for a vacuum to suck it up. Kapton Is a name brand for a synthetic polyamide more like Nylon than Cellophane which is organic or semi organic and older. Cellophane does not have the heat resistance of polyamids. Kapton is mostly used in industrial applications and not consumer ones. \$\endgroup\$ – Passerby Aug 19 at 6:36
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    \$\begingroup\$ Related: What is the purpose of this disk over a Samtec connector? \$\endgroup\$ – Mast Aug 19 at 8:17
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    \$\begingroup\$ The way I heard it was, that besides giving a surface for the pick-and-place machine, it add a bit of protection, for the plastic inside the USB socket, from the heat of the (IR-)reflow oven. \$\endgroup\$ – Gerben Aug 19 at 14:53
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The official name is Pick and Place Pad. While this can refer to hard parts added to bigger or irregular shaped parts for pick and place, it also refers to the tape used for picking.

The tape a high heat, non-conductive tape, used for pick and place machine tips to suck onto to place the connector on a board. It may be Kapton, a name brand Polyimide tape, or may be an alternative brand and type tape. Others use Mylar for example. It just needs to survive movement and typical wave soldering or other automated SMD soldering solutions.

From a manufacturer data sheet: https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=1-1773973-2_Mini_USB_Connectors&DocType=DS&DocLang=EN

enter image description here

For another one, Mylar tape specifically.
http://www.assmann-wsw.com/fileadmin/datasheets/ASS_1456D_CO.pdf
enter image description here

And another: http://www.elstore.it/wp-content/uploads/prodattach/CU04SCM15B0-R0-LF.pdf
enter image description here

It's not intended or required to be removed, as it neither affects the part or usage.

Molex added them onto larger parts since manufacturers/assemblers have moved away from older pick and place mechanical grippers to vacuum pickers. They specifically use Kapton brand tape, cause you know, Molex is big business:

“By adding a Kapton tape surface to the top side of the connector, the Vertical SMT Modular Jacks from Molex can be picked and placed by vacuum heads, delivering a faster, more cost-effective method which is in line with other SMT components in the assembly process.”

https://www.businesswire.com/news/home/20141202005123/en/Vertical-SMT-Modular-Jacks-Molex-Kapton-Tape

And you don't even need straight from the factory parts with this pad on them. This can be added on after the fact, by using tape dots. Great for automating a process. https://smtnet.com/Forums/index.cfm?fuseaction=view_thread&Thread_ID=17372

Issue: A PCB assembly company found themselves with thousands of SMT connectors in inventory, on reels, ready to place. But their pick-and-place equipment was unable to pick them up because of gaps and irregular features on the tops of the connectors.

Solution: NuWay was able to open the carrier tape, apply an adhesive Kapton pad to the top of each part, re-seal the carrier, and rewind the reels. The adhesive pads were circles and rectangles kept in stock at NuWay for just this purpose. The turnaround was fast, and helped the customer make use of thousands of dollars of otherwise unusable connectors.
https://www.nuway.net/solutions

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It's to give the pick and place machine a flat surface to pick it up by, when it's transferring the part from its tape to the PCB.

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    \$\begingroup\$ And I guess most suppliers remove this tape, but some are lazy and leave it on? \$\endgroup\$ – Intrastellar Explorer Aug 19 at 2:35
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    \$\begingroup\$ Well if you want to remove the tape, you have to pay somebody to do that. When removing it is not necessary, leaving it on is just the less expensive option. \$\endgroup\$ – Vladimir Cravero Aug 19 at 6:11
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    \$\begingroup\$ @IntrastellarExplorer no, because it's sometimes an added cost to order pick and place compatible parts, or they have different p&p machine types so don't need a vacuum gripper compatible part. The ones that don't have the tape, most likely never had the tape. See my answer. \$\endgroup\$ – Passerby Aug 19 at 6:14
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    \$\begingroup\$ Wouldn't it be more accurate to say it gives a smooth airtight surface for vacuum pickup, rather than a flat surface? In the connector shown, the surface is already flat, it just has perforations in it. \$\endgroup\$ – Jon Aug 19 at 13:32
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    \$\begingroup\$ Why remove it? It should not present any risk and removal adds cost, it may of course come off in a washing process, but removal is an extra step. \$\endgroup\$ – mckenzm Aug 20 at 4:17

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