Solder SMD on both sides of the PCB (manually) - Page 1
Forum section: electronics / projects

author: KedasProbe
author_rank: Frequent Contributor
timestamp: February 10, 2013, 03:17:30 pm
content: 1) To keep the board small I would put the SMD component on both sides of the PCB.I can see the extra price if machines have to assemble both sides, but if you do it manually are there other reasons why you would avoid to do this?Maybe debugging will be a bit harder.2) And would you solder 0.5mm pitch ICs always last or first, so that in case you damage the board you don't have to try to recover all soldered components.But if you do it first aren't you increasing the risk of damaging the IC.Is there a common practice for manual solder work?

author: scarrier
author_rank: Contributor
timestamp: February 10, 2013, 04:03:48 pm
content: I don't have lots of experience but here is my opinion:1) One of the reason for not doing double sided load is that if you only have 2 layer board, it is not recommended to cut your planes with parts and the traces that go with it so if it is double sided you cannot have a ground plane on the other layer.2) on small board board soldering small IC's after connectors and header is probably a bad idea because it complicates the soldering. There is no problem of soldering fine pitch after other IC's and passive surface mount if you have enough space to solder.

author: daedalus
author_rank: Regular Contributor
timestamp: February 10, 2013, 04:38:13 pm
content: scarrier is right on the money with regards to signal integrity, you really need to think about the ground plane implications on 2 layer boards. That said there are times when you need dual loading on 2 layer boards, just don't expect to fill the whole bottom layer with parts.I do most of my SMT work under a stereo microscope as my eyesight isn't really good enough for 0.5mm pitch work without it. The only thing I would suggest is that you look on ebay for some pcb holders. They are sold for mobile phone repair, and clamp the pcb from the edges, that lets you hold the board flat when you have parts on the back side.as for 2, I would always do high pin density parts first, as for them having as much clearance as possible makes the job easier. I tend to leave anything plastic till as late as possible (mainly connectors), so there is less chance of clipping one with the iron and marking it.If you have a good iron set to the right temperature, you really shouldn't be damaging boards. If you are lifting pads regularly, then you need to sort your technique out.

author: free_electron
author_rank: Super Contributor
timestamp: February 10, 2013, 05:38:48 pm
content: Quote from: scarrier on February 10, 2013, 04:03:48 pmThis is a misconception. Simply because on a doublesided board the thickness of the board material prevents adequate coupling to have a plane effect at all ! That slab of copper on the backside of a doublesided board is so far away that you need to sit in the hundreds of MhZ before you see it as a plane.

author: nctnico
author_rank: Super Contributor
timestamp: February 10, 2013, 07:21:28 pm
content: Quote from: free_electron on February 10, 2013, 05:38:48 pmNonsense. Even for low frequencies a ground plane is extremely beneficial to reduce crosstalk between analog circuits and stay within the noise margin of logic levels. The resistance of a ground plane between two points is always much lower than a trace running between those points.

author: Alana
author_rank: Frequent Contributor
timestamp: February 10, 2013, 09:08:31 pm
content: I did one prototype on 2-sided board with components on both sides due to size limitations. There were no problems with hand soldering. PCB home made with toner-transfer.

author: AndyC_772
author_rank: Super Contributor
timestamp: February 10, 2013, 09:21:23 pm
content: Normally when hand assembling a board I start with the smallest parts then work up to the largest, just so I don't make life difficult for myself by trying to work around a large obstruction. It doesn't really matter if the board is double sided, though obviously it makes sense not to fit tall components to one side of the board if you'll then have to turn it over and work on the other side.If anything needs soldering with a heat gun (eg. parts that have an exposed pad on the underside), it's a good idea to do these first - otherwise you'll risk desoldering parts that have already been fitted.

author: mazurov
author_rank: Frequent Contributor
timestamp: February 10, 2013, 09:30:37 pm
content: Quote from: free_electron on February 10, 2013, 05:38:48 pmThis is true for capacitive coupling only. The benefit of a plane is primary due its low inductance which is not dependent on the distance to the other side.

author: mazurov
author_rank: Frequent Contributor
timestamp: February 10, 2013, 09:36:47 pm
content: Quote from: KedasProbe on February 10, 2013, 03:17:30 pmI start with QFNs and other parts which need to be soldered and inspected from the side (like certain types of crystals). The rest can be soldered from the top and the order of populating doesn't matter.

author: ConKbot
author_rank: Super Contributor
timestamp: February 11, 2013, 12:33:56 pm
content: Start with the annoying packages that youre most likely to bugger up first, that way if you really screw up and break the whole thing you havent wasted much laborDo the low-profile tight pitched stuff where the space around it benefits you, then move onto SMD passives, etc etc. A little TSSOP chip isnt going to get in the way of you soldering a pin header on. That header, if its close enough, will be a big pain trying to do small SMD stuff right next to it.

author: KedasProbe
author_rank: Frequent Contributor
timestamp: February 13, 2013, 01:42:38 pm
content: Thanks for the input.

author: MrsR
author_rank: Regular Contributor
timestamp: February 22, 2013, 01:22:35 am
content: I do a lot of 2 surface .8mm circuit boards. First use solder past. I do the passives first as there low to the board.Just go over the circuit tracks and look to see if an Active component should go first.Most of my passives are 0402 I would suggest using 0603 or larger if possible.I also use a Tool makers clamp to hold the board. RS radio Spares lol. won't have any .8mm or 1mm Boards in stock till April. But they have Positive UV curing 1.6mm boards in stock at present.Have funRachael