Reliable connection between packages and pcb's without solder... - Page 1
Forum section: electronics / projects

author: alank2
author_rank: Super Contributor
timestamp: October 23, 2017, 09:57:07 pm
content: The backstory is this: I'm thinking about the cheapest way to update AVR's remotely. They will have a secure bootloader so that the firmware will be sent to the AVR encrypted and then the bootloader will decrypt it and flash it.I've thought about a PC driven type solution with a cable of some type and a PC side application, which has the advantage of once you have it, you could update device(s) multiple times and you could send the encrypted firmware over email, etc. which would also be convenient. I think they sell those PL2303 ttl uart cables for less than $4, but that would mean dealing with uart and not all of my projects have a crystal. Might be able to get the uart to work even without though.But that would require the work of making the cable/miniboard/pc application which could be done, but it is work.I then thought what about using a cheap throwaway piece of EEPROM. At startup the device could see if the memory is present and then flash if it is found. You can get some for 60 cents that can hold 32K or so. In this case, no cable/miniboard/pc application, but the question is how to interface it?I tried messing around with a PDIP-8 (before the legs are squared with one of those tools), and you can carefully put it into the holes of a DIP socket that is unpopulated and it seems to have a little tension to hold itself there and is probably making a good connection, but I wondered, are there packages that would work better?Can a SOIC-8 be pressed onto pads and get a good connection? What about a DIP-8?I _could_ solder a SOIC-8 onto a tiny board with inline header and put that through holes held at an angle for a good connection, but I don't want to have to solder it!Just thinking out loud here, all thoughts welcome!

author: m98
author_rank: Frequent Contributor
timestamp: October 23, 2017, 10:11:51 pm
content: Getting multiple planar contacts to all touch each other requires them to be lined up perfectly. Sure you could press that SOIC onto its footprint, maybe even make a board cutout to make it nicely self-center on its back, but the contact to the legs will be unreliable. DIP package, however, should make reliable contact if you use through-plated holes.

author: wraper
author_rank: Unknown
timestamp: October 23, 2017, 10:13:52 pm
content: Quote from: alank2 on October 23, 2017, 09:57:07 pmNo.IMO use micro SD card.

author: wraper
author_rank: Unknown
timestamp: October 23, 2017, 10:16:43 pm
content: Quote from: m98 on October 23, 2017, 10:11:51 pmIt won't make reliable contact unless you made the distance between rows of the holes and/or hole size such that it's difficult to insert the chip.

author: ataradov
author_rank: Super Contributor
timestamp: October 23, 2017, 10:51:38 pm
content: DIP pins are naturally spring-loaded, so it will work. The update happens pretty fast, so I would go for that option, of making a small PCB was not an option. But that would imply certain level of training for the user/technician, I would not do anything like this for mass-market rpoduct.There are also sockets for SOIC , which sometimes hold BIOS IC on motherboards. Not sure how much they will add to the cost.And there are obviously sockets for DIP-8 packages, they shouldn't be that expensive.

author: m98
author_rank: Frequent Contributor
timestamp: October 23, 2017, 11:11:26 pm
content: Quote from: wraper on October 23, 2017, 10:16:43 pmIf you have the footprint just right to create a snug but not too tight friction fit, I don't see the reason this shouldn't be good enough for this application.Another Idea: How about connecting a PLCC package in a rectangular cutout with inner sideplating as contacts.

author: mariush
author_rank: Super Contributor
timestamp: October 24, 2017, 01:05:26 am
content: What's wrong with a plain 0.1" header, or 1.27mm or 2mm header? An i2c or SPI eeprom would only need 4 pins (voltage, ground, data , clock) .. just have a 2x3 header (so that you can't plug it the wrong way) on the motherboard to plug the memory in, reboot the thing to read the firmware automatically as your bootloader detects the eeprom in the header, remove when done.You could make it semi-permanent by securing it with a spacer like the ones used on motherboards to install motherboard, or to install m.2 SSD drives to motherboard... you wouldn't even need actual metal spacer, a plain nylon one would be enough ... maybe spacers isn't the right term, i think it's board supports :https://www.digikey.com/products/en/hardware-fasteners-accessories/board-supports/578- those things that let you lock a pcb on both ends so you push one end into your main circuit board in a through hole and then when you press down the eeprom board in the header, it would lock onto the other end.

author: perieanuo
author_rank: Frequent Contributor
timestamp: October 24, 2017, 06:54:58 am
content: Everybody just sacrifice a little space and put holes to program devices. Just deal with wp for eeprom to program it or program it via microcontroller. That is the current practiceEnvoyé de mon HUAWEI NXT-L29 en utilisant Tapatalk

author: technix
author_rank: Super Contributor
timestamp: October 24, 2017, 08:13:01 am
content: With DIPs you can socket them. You solder a socket into the PCB (in most cases your standard DIP footprint will work) and plug the DIP-8 (or SO-8 on adapter board) in there.

author: alank2
author_rank: Super Contributor
timestamp: October 24, 2017, 12:50:51 pm
content: Another idea I had was using one of those cheap PL2303 cables that are a couple of bucks. My concern though is that I have some projects that are 3.3V-5V. I think these cables drive at TTL levels...