Reducing costs! - Page 1
Forum section: electronics / general

author: pirulo123
author_rank: Contributor
timestamp: July 07, 2011, 05:03:59 am
content: Hi All,Well here's the thing my PCB must fit inside a 6x6 inch ~ (15x15 cm) enclosure, but in reality the electronics are very high density and they don't need that much real state the problem is that all the unused space means I'm trowing money away, normally this would be too much but the design I'm working on has 6 copper layers and It makes a BIG difference vs a 2 layer board.I thought about make the primary high density board sit on top of a cheaper 2 layer board by means of male-female connector and a pair of screws to fix it in place, but I'm not convinced...Is this a good idea ? does it make any sense to any of you ? what sort of bad things could happen ?Oh boy I don't want to see their faces when I show them the stacked pcb's... I'm out of ideas....Regards.Pirulo

author: joelby
author_rank: Frequent Contributor
timestamp: July 07, 2011, 05:42:48 am
content: Can't you just mount the PCB in one corner? Or does it slide into the case on a runner and have to be a fixed width? In that case, can't the depth be reduced arbitrarily?

author: ejeffrey
author_rank: Super Contributor
timestamp: July 07, 2011, 07:54:40 am
content: If you can't just move the mounting points to reduce the board size I think your idea is best. Unless the carrier needs to mate with a card edge connector or otherwise carry electrical signals you can even just use a piece of perf board. No connectors needed, just some standoffs and a few screws.QuoteIs this for something intended to be mass produced? In that case make sure your savings in PCB fab outweigh the extra assembly costs.

author: Simon
author_rank: Unknown
timestamp: July 07, 2011, 11:49:44 am
content: yes we need more information

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 07, 2011, 01:10:36 pm
content: Quote from: ejeffrey on July 07, 2011, 07:54:40 amBut bear in mind that PCB size also affects assembly costs due to the number of boards that will go on a panel.Using a high density sub-board is a perfectly reasonable approach if it needs to be big for mechanical reasons. Might long and thin be another option?

author: pirulo123
author_rank: Contributor
timestamp: July 07, 2011, 02:18:17 pm
content: Thanks everyone for your feedback !Quote from: Simon on July 07, 2011, 11:49:44 amTrue!I hope this picture helps a bit.There are 2 routed rails at the bottom and top of the enclosure to flush the PCB way back to mate the pcb interconnects I've not decided what to use that why I draw the '1 breakaway headers... I'm open to suggestion here as well ;-)Please note the big terminal in the front, this one can be soldered into the cheap 2 layer board as well as the rear pcb interconnect....The clearance is not to bad and the stacked pcb's could fit but only if I use one of those weird low profile pcb interconnect...Big mess...Thanks everyone for your reply, your feedback is really appreciated!Pirulo-

author: joelby
author_rank: Frequent Contributor
timestamp: July 07, 2011, 02:30:45 pm
content: That makes a bit more sense. Can you redesign it as a lower density 2 or 4 layer full-size board? How does this compare in total cost to a 2 layer carrier with the small 6 layer daughterboard, with the additional assembly and production steps? What is your anticipated production volume?As long as you can present a few carefully considered alternatives and your reasons for choosing the best (cheapest? Lowest EMI? Fewest parts?), I can't imagine you having any problems.

author: pirulo123
author_rank: Contributor
timestamp: July 07, 2011, 04:56:02 pm
content: Thanks for your feedback joelby,We're still developing this thing, we want to make a few maybe 10 or 12 of them and try them on site...Sadly the numbers don't lie, it's about 800 US dollars for five (5) 6x6 inch 8 layer FR4 PCB (in china) plus shipping.The 2 layer FR4 is less than a third of that, I'll be doing the assembly myself so cost of assembly = monkey on caffeineBecause the board is somehow complex and the signal integrity is key I decided not to re-route this PCB as a 4 or even 6 layer fr4.What about using really cheap and nasty FR-2 (Phenolic cotton paper) as the bed for the high density board ?Thanks.-