board fab with MCU programming requirements? - Page 1
Forum section: electronics / general

author: vixo
author_rank: Regular Contributor
timestamp: September 22, 2019, 11:37:47 am
content: I'm thing of getting a small run of boards fabricated with surface mount components. I sell kits comprising boards and through hole components and have up til not stuck to that formula, but I'm thinking of including a surface mount MCU (atmega328p) pre-fabbed on to one of the boards (through hole MCUs take up so much space). However I don't want to have the through hole components assembled and I'm not sure if that means I can't have the MCU pre-programmed as there will be no ISP header.Do board fab places always use the board and ISP header to program, or might there be some way of pre-programming the chip before it's placed on the board so I can *only* have the MCU soldered in place?

author: Gribo
author_rank: Frequent Contributor
timestamp: September 22, 2019, 12:02:05 pm
content: It depends on how much are you willing to pay for it.Microchip offers programming services for their MCUs, I think there is a very small minimum order quantity for this.TI also offers this service, but their MOQ is in the order of 20K units and up.As an alternative, you can include a small 1.27mm pitch through hole header for programming, or a suitable tag connect footprint.

author: vixo
author_rank: Regular Contributor
timestamp: September 22, 2019, 12:29:28 pm
content: ahh, a tag connect print looks like it might be ideal. I only need this footprint? No power header etc?

author: rea5245
author_rank: Frequent Contributor
timestamp: September 22, 2019, 12:51:01 pm
content: Quote from: vixo on September 22, 2019, 12:29:28 pmNope, just the footprint. I use Tag Connect for all my Microchip PIC boards and I'm very happy with it!- Bob

author: Fire Doger
author_rank: Regular Contributor
timestamp: September 22, 2019, 02:11:53 pm
content: TagConnect is just a replacement for physical header. Ofc 1 pin must be power and 1 ground.One other solution is advanced flying probe machines but needs a more advanced fab house and its limiting.By exposing programming pads you can use simple pogo pins to establish connection to program it.If you want to cut cost you can make custom programming/testing jigs with 3d printed parts and pogo pins.

author: rea5245
author_rank: Frequent Contributor
timestamp: September 22, 2019, 02:20:39 pm
content: Quote from: Fire Doger on September 22, 2019, 02:11:53 pmThat's essentially what Tag Connect is. Their cables cost less than $40 so I can't imagine making a custom jig would be worth the effort.- Bob

author: sokoloff
author_rank: Super Contributor
timestamp: September 22, 2019, 03:03:08 pm
content: One thing to look into is how much (if any) supporting componentry must be present on the board to allow programing for this case where the intent seems to be to program the microprior tofull board assembly... (Do you need supply cap, reset pullup, external crystal, etc?)I'd argue that having those needed components surface mounted by the PCBA house is probably a good idea and won't take away from the kit nature of the kit.

author: langwadt
author_rank: Super Contributor
timestamp: September 22, 2019, 03:10:31 pm
content: Quote from: rea5245 on September 22, 2019, 02:20:39 pma custom jig can also have pins used to test everything else on the board

author: NorthGuy
author_rank: Super Contributor
timestamp: September 22, 2019, 04:22:33 pm
content: Big pogo pins are the best. You're not constricted to any pinout, you can place the holes for pins anywhere on the board where you have space.However, if you don't anticipate changing firmware, you do not need any of these. Microchip can sell pre-programmed chips, and it costs only 10-15 cents per piece. I know they can do PICs. Since they bought Atmel, most likely they can do ATs too:https://www.microchipdirect.com

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 22, 2019, 04:37:40 pm
content: Quote from: Gribo on September 22, 2019, 12:02:05 pmAbout 20 cents for a mega328, $29 setup and $60 minimum order (I think the latter includes the part cost).

author: vixo
author_rank: Regular Contributor
timestamp: September 23, 2019, 11:57:17 am
content: Quote from: Fire Doger on September 22, 2019, 02:11:53 pmI program my atmega chips using an AVRISP MKII, which needs the board to be powered *in addition* to the programmer. Is there a kind of programmer for which I only need the 6 pin ISP header? Or you mean that the tag connect will have additional pins for power and ground? If I can program via a tag connect header I could program the boards myself, as I'm only doing very small runs

author: Psi
author_rank: Super Contributor
timestamp: September 23, 2019, 12:03:55 pm
content: Yep, i also use tag connect.But if you want to go ULTRA cheap/diy you can put a row of 2.56mm holes on the pcb and make a clip-on adapter using a clothes peg, some hot glue and a 2.54mm header block.etc

author: SMTech
author_rank: Frequent Contributor
timestamp: September 23, 2019, 12:16:24 pm
content: Psi's solution is quite neat really. We make a few boards where the client doesn't populate the programming header and presumably they are relying on manually applying pressure or using a rig like this. Personally this or a pin based jig is the route I would go and you can add your own power into the pinout if you require.PICKits supply power over the 6pin header, if you like PICs, not much help if you're an arduino fan. Of course if you are an arduino fan then you might want to buy the chips pre-flashed with the bootloader and leave the rest to the kit builder.. horses for courses.

author: vixo
author_rank: Regular Contributor
timestamp: September 23, 2019, 12:21:54 pm
content: Quote from: SMTech on September 23, 2019, 12:16:24 pmi don't use arduino, I just always used atmel chips - though I gather that you can modify the AVRISP to provide power, so no problem there

author: Fire Doger
author_rank: Regular Contributor
timestamp: September 24, 2019, 05:19:05 am
content: Quote from: vixo on September 23, 2019, 11:57:17 amDepending on each board it may require to power up all 5V / 3.3V rails and it may have loads that many programmers and even usb can't supply (that's why expensive programmers have external power supply).You can use Vcc pin from tag connect to power the board but you have to make an adapter after programmer to supply the required voltage (and attach programmers Vcc on this rail if it needs to detect voltage) something like this for example:If you take a look at apple's motherboard you will see many exposed pads spread all over the place.This jig has many pins and use the exposed pads to do more than programmingThere also thick head pogo pins for holes