Surface Mount Questions.....
DarrenY
Posts: 61
Hello People,
So I have prototyped my prop based design on a breadboard.
The next step is to get a proto PCB board layout done in Eagle and get someone to make it for me (BatchPCB?)
When prototyping on my breadboard I selected components available in both DIP/SMT packages so I could use the DIP for breadboard proto and SMT for PCB proto.
I have next to no experience with PCB design and have the following questions:
1) Is it possible to get the PCB produced and returned to me with the SMT components pre-installed?
2) How do you go about attaching SMT components like the Prop QFP/QFN chip’s?
3) What’s the difference between the QFP/QFN chips – i.e. advantages/disadvantages of each design?
4) Am I going to have to buy expensive equipment to do this?!
I realise some of the questions above run into each other, but I am hoping you can help me clear these things up!
Thanks.
DarrenY
So I have prototyped my prop based design on a breadboard.
The next step is to get a proto PCB board layout done in Eagle and get someone to make it for me (BatchPCB?)
When prototyping on my breadboard I selected components available in both DIP/SMT packages so I could use the DIP for breadboard proto and SMT for PCB proto.
I have next to no experience with PCB design and have the following questions:
1) Is it possible to get the PCB produced and returned to me with the SMT components pre-installed?
2) How do you go about attaching SMT components like the Prop QFP/QFN chip’s?
3) What’s the difference between the QFP/QFN chips – i.e. advantages/disadvantages of each design?
4) Am I going to have to buy expensive equipment to do this?!
I realise some of the questions above run into each other, but I am hoping you can help me clear these things up!
Thanks.
DarrenY
Comments
Disclaimer: I've not done ANY PCB stuff myself yet, but have been investigating.
1. Yes - but it depends on which PCB manufacturer you use. I suspect most will want you to order a significant quantity though, and it goes without saying that it'll add significantly to the cost.
2. Sparkfun have a couple of tutorials / videos of SMT soldering...
HTH.
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Cheers,
Simon
www.norfolkhelicopterclub.co.uk
You'll always have as many take-offs as landings, the trick is to be sure you can take-off again ;-)
BTW: I type as I'm thinking, so please don't take any offense at my writing style
It is simple, but requires patience, and small tools.
Resistors/condensers of the 1206 series, are big enough not to cause problems, samller ones exist, but are more troublesome. Till .65 mm pitch works very well, .5 mm pitch is a bit too laborious for a soldering iron, .4 mm is insane (soldering iron)
Have fun
2. A flux pen, this helps a lot especially for rework.
3. Solder paste
4. A fine iron
Then practice and do the one thing that the "big boys" can't do so easily, test and inspect every joint.
Get the SMT propeller with the legs rather than the legless type.
Graham
I use a cheap toaster oven to reflow the solder joints.· Here's a link with instructions: http://www.stencilsunlimited.com/smt_stencils/smt_stencil_article_page1.htm
You don't have to have a stencil. A syringe with solder works well for boards without a lot of components and no small lead spacing.·A magnifing light for larger (>0805 & .65mm lead spacing) components or a cheap stereo microscope for the smallet components will neccessary.· If your board has a lot of components or small lead spacing it is best to use a prototype stencil (around $150).· I would recommend that you start with nothing smaller than 0805 size components and IC's with lead spacing of 0.8mm minimum. The propeller is 0.8 mm and most·SO chips have a 1.27mm (0.050") spacing.· These are actually quite easy to place and solder.· Regardless of the size you MUST inspect all solder joints before applying power if you want to avoid frying something.· After much practice you can get down to 0402 size components and a lead spacing of 0.5mm (0.020").· It's painstaking work to use the smaller components but the latest and greatest chips are getting smaller and smaller and don't leave you any choice if you want to use them.· As far as leadless chips go I would stay away from them until you master leaded chips.
Good Luck
Tom
Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
Tom
www.heinc.com/xytronic/Images/Drag%20Soldering%20107.wmv
A dress is not required
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Brian
uController.com - home of SpinStudio
I watched the video and my first thought is the flux must be very sticky to keep the part from moving. It looks like just the thing for rework or small jobs.
Tom
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Brian
uController.com - home of SpinStudio
I used:
-Solder rework Flux paste. Comes in a 10cc syringe and is quite thick. Helps hold components in place too [noparse]:)[/noparse] $16NZD
-Soldering iron with tiny tip (though ive heard tiny tip isn't needed) $400NZD Though any good iron with small tip is ok. This iron was overkill :P
-Standard hobby solder (about 1.5mm dia)
The prop chip (QFP package) was very quick!
1) Put flux paste on every pin...just drag it along them.
2) Position the Prop.
3) Heat the first pin. There is a small amount of solder on the PCB pad from the fab process which melts and holds the IC in place. No need to add extra solder yet.
4) Slowly run the iron down the opposite side of the IC to the first pin you just soldered. This should stick all the pins down.
5) Repeat for sides 2 & 3 and then side 1.
6) For good meassure I put a tiny bit of solder on the iron and ran it down each side also.
For the 0603 components
1) Flux the pads
2) Position the component right beside where it is being soldered, and in the right orientation.
3) Heat one of the pads till the solder melts (which is there from fab process)
4) Tap the component onto the pads. It should stick the the pad you melted. I used a tiny screwdriver.
5) Put a tiny bit of solder on the 2nd pad, and then on the 1st pad
Hope that helps!
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-Alec
My our page
I have read many warnings about hand soldering ceramic smd capacitors, specifically that it will cause them to develop cracks, leading to open circuits. However, I've read in this forum and elsewhere that everybody seems to do it with no ill effects. Has anybody actually had a cap fail? Or would you even know if it wasn't in a critical part of the circuit?
Tom
Hmmm i hadn't heard about that. I didn't see any crack, and there seem to be no adverse effects so far (my board worked first try!)
I did have the iron up at aourn 400deg c though so heres hoping !
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-Alec
My our page
All I can·contribute to this is:
I've sold hundreds of IC's SMT in the last months by hand, also 0603 and 0805 capacitors.
I had not never problems with those caps, neither IC's.
I used flux gel that comes in syringes...· Like Basil coments before. (same method).
Although I found,·that is extremelly easy, and it is not necessary to use small and thin iron solders, I used a big one without any consequences.
In fact I think it is better....
Put a considerable good quantity of gel before sold the IC, (Like Leon said before).
Place the IC (QFP)...in the correct position solding some pins, doesn't care, if you do many short circuits in some pins at this point.
Then put the flux, and then·weld it, running with the iron between all pins...and voila !!!
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Regards.
Alberto.
Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
So many variations
Looks like I need to sit down and digest all these methods and then give each a try and see which works for me - i'm sure that when I get into it I will have more questions but for now - thank you to all those who have made suggestions. I think i'm going to give the Basil/BTX method a try first.
Cheers!
I'm not suprised a bigger iron worked well, too often small irons are used and they have to be left in place for a long time to melt the solder. I generally prefer the hot and fast approach. Using low temperatures solders makes a smaller iron more practical.
Graham
You'll find that is much more easy that you think !!
@Graham
Also I can't believe when I discover the flux gel ...it is great !! I tried with so many pencils...all works fine, but the "gel" get the first place for me.
Also I was using a very small iron solder...but I changed by the common one, when I saw a PACE soldering station for this purpose, and the "Single Sided Chisel" was so big like my old standard 30 Watt solder.... [noparse]:)[/noparse]
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Regards.
Alberto.
In sum, be patient and get hands on experience - talk can only go so far.
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"Everything in the world is purchased by labour; and our passions are the only causes of labor." -- David·Hume (1711-76)········
Thought id try my cheapo iron on some 0603's and TSSOP packages...my $40 iron with standard tip is easier then $400+ soldering station with very fine tip!
If only I had of tried sooner...
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-Alec
My our page
Been soldering smt stuff by hand for 10+ years.I personally use the big
tipped iron/drag method.Get the the heat in quickly,get it away quickly.
Never used solder gel, I use fluxed solder braid 1.5mm to clean up the
bridged pins afterwards, I found paper glue, Prit Stick, or Copydex to glue
the chip in position works just fine.No problems up to 240 pins @ 0.5mm.
Regards Ian
Nope BGA looks like a nightmare,I would imagine you need some sort
of oven, faith, and a lot of luck!!
I'm never going to use it, so if anybody wants a 196 ball BGA 1mm
spacing ADSP21065 for practice I'll send it to them.
Ian.
QUOTE: www.radio-electronics.com/info/manufacture/soldering/smt-soldering/bga-solder.php
For BGA soldering, the solder balls on the package have a very carefully controlled amount of solder, and when heated in the soldering process, the solder melts. Surface tension causes the molten solder to hold the package in the correct alignment with the circuit board, while the solder cools and solidifies. The composition of the solder alloy and the soldering temperature are carefully chosen so that the solder does not completely melt, but stays semi-liquid, allowing each ball to stay separate from its neighbours.
Registration of the package is probably the biggest problem as is profiling the reflow oven. The other problem is that with high density bgas you need multilayer pcbs, so your protos can be expensive and you can stuff them up until you get the reflow profile right (assuming you have some method of aligning).
*Peter*
Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
Post Edited (Leon) : 9/20/2007 5:45:31 AM GMT
What he used was a focussed IR Lamp to heat the BGA Device.
He had a small CCTV camera with a macro focus lens watching the gap between the BGA and the board so you could see some of the solder balls. He then turned on the IR lamp and waited until the
BGA "dropped" which was the 1st phase of the solder going plastic. It then does a second "drop" as the solder flows properly, at which time he switched off the IR source.
The IR lamp he was using was basically a small, relatively powerful incandescent heat lamp with a mask to ensure it only heated the BGA and immediately surrounding area.
It was a fascinating demonstration and the job turned out to be very, very good under examination with a microscope.
The BGA was positioned on the board using the CCTV camera to ensure the registration was pretty close, and held in place with a little flux gel.. but as the solder melts it automatically aligns the BGA properly
on the pads. You can actually have quite a bit of mechanical misalignment and it will just pull itself into place with the surface tension of the solder.
I'd like to try it on at least a small device. I know there will be nay sayers but bgas are not magic they are just lots of solder balls.
Graham