[hackspacebristol] Soldering QFN packages

Jolyon Jenkins jolyonjenkins at googlemail.com
Fri Jul 11 10:08:25 UTC 2014


Wow, thanks. Lots of great tips there.


On 11 July 2014 10:17, <si at simonchambers.co.uk> wrote:

>  I’ve reflowed hundreds boards in my own [pizza/toast type] oven for a
> year or so - here’s a bit of a brain dump of what I’ve found/experienced:
>   - Even for one board, its quicker and easier than using hot air rework
> for a fresh board - it’s also a lot less violent than using hot air too.
> However hot air rework is essential if you need to remove & replace parts
> of course.
>   - Unless there are only a handful of components, I reflow my boards now.
> So much quicker and reliable.
>   - Get a stencil! You can use a syringe with tips, but unless if its for
> a one-off/small part count board with large pads, its hard to get the
> correct quantity on the board. For cheap stencils, I currently get them
> from www.elecrow.com - around $20 + shipping. Don’t bother with the
> enoooormous machine mounting stencils, just get the smaller cut out ones -
> cheaper shipping. Their boards are pretty good value too, however the drill
> hit sometimes can be a little off. I find them quicker at getting them
> made+shipped than Iteadstudio+seeedstudio.
>   - On the subject of PCBs, I thoroughly recommend www.hackvana.com if
> you want quality and cheap. He’s an Aussie bloke who lives in Shenzen who
> decided to offer quality PCBs. He has no online quoting system, but you can
> contact him directly by email and on #hackvana on Freenode. The quality
> rivals most western suppliers, and also if you have anything unusual he can
> cater for it - makes it much easier speaking to someone with English as
> their mother tongue.
>  - Again on PCBs, I rarely order from the UK/Europe now. You can get a PCB
> made in China, shipped (using DHL/FedEx) to your door in a week. Not only
> is it quicker than a lot of UK/European suppliers (unless you pay super
> money for superfast turn-around), you get 10 boards, for around 3rd of the
> price. Speaking to several people on the ground in Shenzen the equipment in
> the Chinese factories is the latest kit and top notch quality - better than
> a lot of European fabs. The cheap price is due to the highly competitive
> environment over there and that a lot of Fabs have had heavy investment in
> equipment (helped by the Government making it difficult for individuals
> take cash out of the country).
>
>   - To mount the stencil, you need to have a right angle that you can push
> the board into and then you can tape the stencil along one edge, like a
> flap. You can get premade right angle boards, but I personally just use two
> scrap PCBs of the correct thickness and stick them together.
>   Another alternative to mounting the stencil, if you design it from the
> beginning, is to use a jig like this -
> http://www.hoektronics.com/2012/10/27/super-simple-smt-stencil8/ . You
> can buy a premade CNC’ed one from here:
> https://www.tindie.com/products/arachnidlabs/pcb-tooling-block-full-grid/ .
> This makes it a lot easier and quicker to setup. The guy who
> manufacturers/sells that CNC’ed on tindie is a active member of the London
> hackspace (Nick Johnson) - so I’m sure if Bristol Hackspace wanted to get
> one, he would happily offer a decent discount. He’s frequently on #hackvana
> and #london-hack-space on Freenode.
>   - When reflowing, the key temperatures I find are 150C, >200C (>220C for
> PB-Free). 150C allows the board and components to pre-heat up. Not hot
> enough to do damage, but hot enough to allow everything to reach the same
> temperature. You want to hang around there for 40-60 seconds. Then you want
> to heat it up fairly rapidly. When above >200C (>220C) the solder will
> start ‘reflowing’. You want to hit the peak temperature, and then shut off.
> Now you need to cool down fairly rapidly to prevent damage to the parts
> (not too quickly though). Personally I find opening the door on my oven is
> sufficient. Keeping it closed takes too long to cool down.
>   - I did make a controller with proper reflow profiles, etc, etc. It now
> just gets it to 100C (preheat the oven), then 150C and hold it for a max of
> 30-40seconds and finally heats up to 220C/240C (PB/PB-Free). Once it hits
> peak temperature, it buzzes to open the door.
>   - Don’t put the boards on a wire rack. Put it on a sheet of metal or
> similar. Note, make sure that the metal won’t bow as its heating up!
> Otherwise your carefully placed components will become scattered all around
> the oven, or even worse, become dislodged and reflow in the wrong place.
>   - Part placement (for the passives especially) is fairly uncritical,
> when the solder heats up, they’ll flow/move into the correct place.
>   - As Tom said, until you’ve done the process once or twice, don’t expect
> perfect results - especially if you’re doing QFNs. It takes a little bit of
> knack to get it right (but not too much!).
>   - Certainly early on, put a spare/scrap/similar board in the oven as
> well with a thermocouple attached to one of the pads/holes. This way you
> can measure the actual temperature of what the board is - rather than the
> ambient temperature in the oven. Otherwise you may find that the oven
> doesn’t get to sufficient temperature to properly reflow.
>   - Kapton tape is your friend, get some! You can get genuine 3M stuff but
> its hideously expensive. The cheap Polyamide tape is just as good for this
> type of work.
>   - EEVBlog/Dave Jones has a couple of good videos to get you started here
> - https://www.youtube.com/watch?v=FNNRoXZom30 /
> https://www.youtube.com/watch?v=JA-vi2iQ5vA Worth a watch.
>
> Sorry for the length but I hope this helps!
>
> Cheers,
> Si.
>
>
>
> *From:* Tom Gardner <tggzzz+hs at gmail.com>
> *Sent:* ‎Friday‎, ‎11‎ ‎July‎ ‎2014 ‎10‎:‎03‎ ‎AM
> *To:* Bristol UK Hackspace <hackspacebristol at lists.aktivix.org>
>
> Arthur used the oven last night for the first time since modification.
> Before doing the "real" board, it might be worth trying a couple of
> sacrificial boards in order to assure yourself that you've got everything
> (temp, solder, flux, phase of moon) set up correctly.
>
> I haven't done any SMD soldering, but I will have to in the near future.
> The links below may, or may not, be helpful - I'd be grateful for any
> experience/comments.
>
>
> http://product.tdk.com//mlcc/en/applicationnote/pdf/30_rework_methods_for_surface_mount_mlccs.pdf
> http://store.curiousinventor.com/guides/Surface_Mount_Soldering/Tools/
> http://articulationllc.home.comcast.net/~articulationllc/sm0402.htm
>
> http://www.avrfreaks.net/modules/FreaksArticles/files/15/Low%20Cost%20SMD%20Soldering%20Guide.pdf
> http://www.dlharmon.com/solder/smd.html
>
> I'm also going to be investigating using my slow cooker as a heat bath,
> since it will be more convenient for me to apply paste, then components,
> and then heat at home.
>
> (No I won't be putting Pb solder in the cooking vessel! My slow cooker has
> a solid aluminium exterior that gets hot.
>
>
>
> On 11 July 2014 09:43, Jolyon Jenkins <jolyonjenkins at googlemail.com>
> wrote:
>
>> Hello
>> I'm working on a project that will need me to solder some tiny QFN chips.
>> I've never done this before. I see that the hackspace has a solder reflow
>> oven but is there someone who could hold my hand on my first attempt? I
>> guess I will need some stencils, unless the hackspace has them?
>>
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>>
>
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