Noob question; which is pin 1 on this LQFP 44? - Page 1
Forum section: electronics / beginners

author: CMagnusJ
author_rank: Newbie
timestamp: December 09, 2017, 09:53:03 pm
content: So this chip made me be a bit unsure, it has 2 distinct markings.Which one is pin 1 (which should correspond to the dot marking on the PCB) ?I'm 90 % sure it's the one with the extra dot in the lower left corner, just want to be sure before I mount it./M

author: abraxa
author_rank: Frequent Contributor
timestamp: December 09, 2017, 10:08:03 pm
content: Looking at ICs of the 12C5A family online, they all only have one marking and indeed it's in the same place as the one with the dot. Very odd to me. Are you sure it's genuine?

author: CMagnusJ
author_rank: Newbie
timestamp: December 09, 2017, 10:10:21 pm
content: Thanks,most likely not genuine, it's made of chinesium, ordered from the usual suspects../M

author: Jeroen3
author_rank: Super Contributor
timestamp: December 09, 2017, 10:21:37 pm
content: Next time look at the tape orientation.ST also has parts with a molding artifact, it's highly annoying in hand assembly.I would say the one on the upper side is the correct marking. The one with circle is the molding artifact.

author: AndyC_772
author_rank: Super Contributor
timestamp: December 09, 2017, 10:48:39 pm
content: I'd have said the one at the bottom is the correct marking. Usually, if there's more than one, it's the smaller dot that's the "real" one.Perhaps you can get another clue by measuring. Does the chip have multiple power or ground pins that might be connected together? Compare the resistance between pins that would all be joined together in each possible orientation.

author: 2N3055
author_rank: Super Contributor
timestamp: December 10, 2017, 10:48:25 am
content: The one on the bottom left looks like fiducial mark, and would be most likely a pin one marker.Also most of manufacturers still follow the rule that you orient the chip so you can read the text on it and then compare it to datasheet....And you can't measure anything, according to datasheet darn thing has only one GND pin....

author: stmdude
author_rank: Frequent Contributor
timestamp: December 10, 2017, 11:03:16 am
content: Quote from: Jeroen3 on December 09, 2017, 10:21:37 pmThat, and that the text is printed 90 degrees rotated from where you'd expect Pin 1 to be.

author: Twoflower
author_rank: Frequent Contributor
timestamp: December 10, 2017, 11:16:30 am
content: Not only the dot seems fishy. Also the datasheet says that the package has a different corner between pin 1 and pin 44. I wouldn't trust this chip.

author: martinator
author_rank: Contributor
timestamp: December 10, 2017, 11:22:02 am
content: As already mentioned , you should be able to at least find the GND pins. They may be dead shorts but probably have 1 or 2 ohms between them.

author: 2N3055
author_rank: Super Contributor
timestamp: December 10, 2017, 11:39:31 am
content: Quote from: martinator on December 10, 2017, 11:22:02 amThere is exactly ONE (1) GND pin..

author: Jeroen3
author_rank: Super Contributor
timestamp: December 10, 2017, 11:45:40 am
content: The Vdd pins should be shorted internally as well.

author: martinator
author_rank: Contributor
timestamp: December 10, 2017, 11:56:42 am
content: If it's genuine then pin 1 should be the one below the dot? The letter 'C' looks a bit out of alignment but there are photos of other packages(DIP) in google images with the C having the same alignment, but screenprinted on not etched.

author: Swake
author_rank: Frequent Contributor
timestamp: December 10, 2017, 01:15:29 pm
content: No markings on the bottom?Are the 4 corners the same size (also check on the bottom)?

author: amyk
author_rank: Super Contributor
timestamp: December 10, 2017, 05:26:19 pm
content: I believe STC is fabless so there could be packaging variation between different fab locations, but all the pictures of this part I could find on the Internet seem to show the lower left as being the correct pin 1 marker.

author: BrianHG
author_rank: Super Contributor
timestamp: December 10, 2017, 05:46:50 pm
content: Nope, it's the faint dot at the top left next to the STC logo.The other 2 are part of the IC' plastic manufacturing.

author: Kalvin
author_rank: Super Contributor
timestamp: December 10, 2017, 05:51:28 pm
content: If you google using words: stc 12C5Aand then look at the images found, you can see some variation on the markings. But the lower left corner is always having the marking.

author: Howardlong
author_rank: Super Contributor
timestamp: December 10, 2017, 05:56:14 pm
content: Perhaps using the diode mutlimeter setting might help in identfying Vdd & GND by probing protection diodes and inferring from that?

author: AndyC_772
author_rank: Super Contributor
timestamp: December 10, 2017, 06:03:17 pm
content: Quote from: BrianHG on December 10, 2017, 05:46:50 pmWell spotted, I concur.

author: Kalvin
author_rank: Super Contributor
timestamp: December 10, 2017, 06:12:25 pm
content: Quote from: AndyC_772 on December 10, 2017, 06:03:17 pmMy bet is still on the lower left corner as every STC 12C5A device in the Google Image has the marking on the lower left corner independent of other possible markings.

author: Cyberdragon
author_rank: Super Contributor
timestamp: December 10, 2017, 08:29:54 pm
content: Quote from: AndyC_772 on December 10, 2017, 06:03:17 pmWhat dot? All I see is a white speck that looks like an artifact like the ones under the T.

author: chrisl
author_rank: Regular Contributor
timestamp: December 10, 2017, 09:14:56 pm
content: From their datasheet... I bet my $ on the lower left pin.

author: BrianHG
author_rank: Super Contributor
timestamp: December 10, 2017, 10:51:46 pm
content: Quote from: Cyberdragon on December 10, 2017, 08:29:54 pmHmmm, the larger faint circle around the white spec may be a Jpeg apparition, if there truly is no larger indented circle in the plastic there, then it is not pin 1.I just put the image through a Gaussian blurr of 3 pixels in diameter, the larger indented sphere around where the white dot was still shows. Could be a fluke manufacturing flaw dent.@chrisl photo says I'm wrong and pin 1 is at the bottom left of the package.

author: BrianHG
author_rank: Super Contributor
timestamp: December 10, 2017, 11:13:28 pm
content: Perhaps as a valid test, using a DVM in diode mode, shouldn't it see 0.7v approx in reverse across VDD & GND while a larger voltage forward?Where as any 2 IO pins should always read the above the 0.7v larger voltage in either direction?