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alexeames
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Re: Gertboard shipping date.

Fri Sep 21, 2012 6:23 am

exartemarte wrote:
alexeames wrote:[..] and that's enough to realise I need thinner than 1mm solder.
That thought occurred to me when I was looking at some of those components in the bags. I've ordered some 0.4mm solder, and I don't think I'll make a start until it arrives. Obviously I've seen smd components in situ, but I've always regarded those boards as machine-assembled - I've never thought about what it might be like to solder such tiny pieces by hand.
Let's just say tweezers are essential - the finer the better :lol: I've got a photography loupe for examining the finished joints. If you use reading glasses, they will be essential here too.

Mortimer if you've got a fine tip, your Antex should be ok. I'm using the 18 Watt Antex. Standard tip was fine for the large resistor, but I swapped out for a fine tip for the other, smaller ones.
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Re: Gertboard shipping date.

Fri Sep 21, 2012 7:07 am

I'll be borrowing a fancy solder station from work. It has a nice fine tip on it.
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Re: Gertboard shipping date.

Fri Sep 21, 2012 7:44 am

I found that the common 0.7mm solder worked well, 1mm is probably just a little to thick to be able to control how much solder is applied.

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Re: Gertboard shipping date.

Fri Sep 21, 2012 7:47 am

domesday wrote:I found that the common 0.7mm solder worked well, 1mm is probably just a little to thick to be able to control how much solder is applied.
I've already done 6 out of ~20 SMD components, so I'm going to try splitting what I've got with a knife. If that doesn't work, I'll go and buy some. Seems a bit silly to drive 12 miles each way for that though - of course, once in Maplins, who knows what else could happen? :evil:
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Re: Gertboard shipping date.

Fri Sep 21, 2012 7:51 am

alexeames wrote:of course, once in Maplins, who knows what else could happen? :evil:
Indeed, you might come away with a ride-on remote control car and a car stereo but no solder knowing maplin these days :lol:

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Re: Gertboard shipping date.

Fri Sep 21, 2012 8:23 am

I seem to remember form my soldering course (for fine components) that you flux board (Very important), put solder on tip, but don't apply solder wire to joint - just use what's on the tip. So solder wire thickness should be irrelevent.
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Re: Gertboard shipping date.

Fri Sep 21, 2012 9:29 am

In my day (long time ago in a galaxy far far away) we tinned the iron, applied iron to joint and flowed the solder onto the component lead at the joint.

But things could have changed with your modern surface mount thinghys :)

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Re: Gertboard shipping date.

Fri Sep 21, 2012 9:38 am

Components are too small nowadays I believe.
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Re: Gertboard shipping date.

Fri Sep 21, 2012 9:45 am

Another reason may be that 'the old way' of melting solder against a hot component has a higher risk of damaging such small components. A wire lead resistor, the temperature achieved at the component body is going to be quite a bit lower than the point being heated to melt solder, as the lead acts a bit like a heat sink/radiator. When the metallic contact is part of the component body, heating the component effectively applies all the heat to the component itself.
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Re: Gertboard shipping date.

Fri Sep 21, 2012 9:52 am

jamesh wrote:Components are too small nowadays I believe.
Certainly too small for convenient hand assembly, but necessary for miniaturisation. Making things small apparently reduces costs: I'm not sure why that should be so - traditionally it certainly wasn't - but according to Eben keeping the Pi below a certain size was necessary in order to keep the price down, and he knows what he's talking about.

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Re: Gertboard shipping date.

Fri Sep 21, 2012 10:02 am

exartemarte wrote:Certainly too small for convenient hand assembly, but necessary for miniaturisation. Making things small apparently reduces costs: I'm not sure why that should be so - traditionally it certainly wasn't - but according to Eben keeping the Pi below a certain size was necessary in order to keep the price down, and he knows what he's talking about.
Probably because in larger scale production where automation is key, the size of the components matter less when it comes to actual assembly, but plays a big part in the material cost. If everything was assembled by hand, then clearly such small components would clearly increase the cost, because the extra man-hours required to work with them.
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Re: Gertboard shipping date.

Fri Sep 21, 2012 10:19 am

The costs relating to the size of the pi are more to do with the PCB cost. Multi-layer PCBs are expensive to produce so the more you can cut from a single sheet the better. In other words if you can reduce the PCB size by 20% that is 20% more boards you get for the same cost.

Modern pick and place machines can work with very tiny components with great accuracy and speed. Unlike hand soldering the machine puts a small dot of solder paste on the pads and then places the component. The paste acts as a sort of glue to hold it in place, the whole board is then heated in an oven to set the paste.

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Re: Gertboard shipping date.

Fri Sep 21, 2012 10:30 am

The paste acts as a sort of glue to hold it in place,
Can us humans use this method or is it a machine-only technique as it would be handy for bridging the USB polyfuses on rev1 boards - my little wiring attempt works but looks atrocious! :)

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Re: Gertboard shipping date.

Fri Sep 21, 2012 10:36 am

exartemarte wrote:
jamesh wrote:Components are too small nowadays I believe.
Certainly too small for convenient hand assembly, but necessary for miniaturisation. Making things small apparently reduces costs: I'm not sure why that should be so - traditionally it certainly wasn't
With printed circuit board manufacture you pay for various things

board area
layer count
smaller than normal design rules. This can add to your cost if you make the board too small but if your components have high density connections you are going to have to use small design rules regardless of overall board size.
anything "special" (blind vias, burried vias, special surface finishes, special board materials etc)

With assembly making things smaller means that more boards can be loaded on the pick and place machine at once, an obvious saving in manual handling. Double sided assemblly obviously increases costs but afaict it's pretty much unavoidable with processors as fast as the one on the Pi and once you have put a few caps on the bottom you may as well put other stuff there too.

So there is a sweet spot. Try to make things TOO small and you will end up spending lots of money on extra layers, blind and burried vias and so-on. Make things too big and you will just waste material and increase manual handling.

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Re: Gertboard shipping date.

Fri Sep 21, 2012 10:52 am

simplesi wrote:
The paste acts as a sort of glue to hold it in place,
Can us humans use this method
Humans can certainly use solder paste though it takes skill to place small components without mechanical assistance. Also ideally you want a stencil for putting the paste down to control the ammount and location.

commercial stencils are laser-cut but it is also possible to make stencils by etching which should be possible to DIY.
or is it a machine-only technique as it would be handy for bridging the USB polyfuses on rev1 boards - my little wiring attempt works but looks atrocious! :)
Solder tends to bunch up when it melts regardless of whether it originally started as wire or paste. So it's pretty difficult to bridge a component with it other than by creating a massive blob.

Probablly the neatest way to fix the polyfuse issue would be to desolder the polyfuses and replace them with zero ohm links. But really you want a set of heated tweezers for that and those don't come cheap.

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Re: Gertboard shipping date.

Fri Sep 21, 2012 10:56 am

I've just finished soldering the surface mounted components. Am I glad I invested in one of these:

http://www.maplin.co.uk/22w-fluorescent ... lamp-47980

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Re: Gertboard shipping date.

Fri Sep 21, 2012 11:44 am

simplesi wrote:
The paste acts as a sort of glue to hold it in place,
Can us humans use this method or is it a machine-only technique as it would be handy for bridging the USB polyfuses on rev1 boards - my little wiring attempt works but looks atrocious! :)

Simon
Hi

Having tried it I managed to get a short circuit using solder paste but other people have had more success. I now use very fine (0.4mm solder Lead/Tin/Silver) instead.

Cheers

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Re: Gertboard shipping date.

Fri Sep 21, 2012 12:27 pm

Is anyone else finding the tactile switches supplied in the Tandy kit are really not an easy fit to the hole dimensions? Are they definitely correct? I don't want to force it.

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Re: Gertboard shipping date.

Fri Sep 21, 2012 12:30 pm

el10t wrote:Is anyone else finding the tactile switches supplied in the Tandy kit are really not an easy fit to the hole dimensions? Are they definitely correct? I don't want to force it.
It fact I'm now convinced they are wrong. There is no way to bend the pins enough without them breaking off. Looks like I'll have to stop for now until I can get some that fit.

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Re: Gertboard shipping date.

Fri Sep 21, 2012 12:35 pm

el10t wrote:Is anyone else finding the tactile switches supplied in the Tandy kit are really not an easy fit to the hole dimensions? Are they definitely correct? I don't want to force it.
The tactile switches are a bit fiddly the legs need to be spread out a bit, you will see Gert had the same problem with his switches mentioned in his construction guide.

The best technique is to spread the legs slightly so that the tips of the pins line up with the holes and then press down each corner of the switch with the blunt end of a pencil or something to push it home.
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Re: Gertboard shipping date.

Fri Sep 21, 2012 12:37 pm

el10t wrote:Is anyone else finding the tactile switches supplied in the Tandy kit are really not an easy fit to the hole dimensions? Are they definitely correct? I don't want to force it.
Not tried them yet.
Just finished the IC sockets. I managed to use my 1mm solder to finish off the SMDs. I tried splitting it, but it was too hard and didn't help much, so I carried on. I got a bit better at it as I went. The smaller resistors look a bit poorly done, but they should still work - I hope.
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Re: Gertboard shipping date.

Fri Sep 21, 2012 12:40 pm

I criticised Tandy earlier in the thread for the delay to delivery. I'd now like to turn that around and publicly say "thank you and good job, Tandy". You have been really responsive to questions raised, including mine above.

I'm going to give spreading the legs a go now (oo-er, obviously) and see if I can get these switches in place :D

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Re: Gertboard shipping date.

Fri Sep 21, 2012 12:42 pm

I'm going to old off until I can get one ready-made. Is that going to be an option in the future? I'm useless with a soldering iron!

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Re: Gertboard shipping date.

Fri Sep 21, 2012 12:45 pm

I've started an assembly thread here...

http://www.raspberrypi.org/phpBB3/viewt ... 42&t=17987

...as it seems to me that in our excitement, we're wandering off topic in this thread. :D

Come and join in the fun :D
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Re: Gertboard shipping date.

Fri Sep 21, 2012 8:29 pm

piglet wrote:I'm going to old off until I can get one ready-made. Is that going to be an option in the future? I'm useless with a soldering iron!
I doubt it.

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