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Second attempt at SMD soldering

Andrew J

Following on from this discussion where a lot of tips came my way, I thought it only right to give it another go:  https://www.element14.com/community/thread/72152/l/first-attempt-at-smd-soldering  I really feel like I've joined the club now I burnt the end of one of my fingers image  On the plus side, none of the parts went pinging off.

 

In no particular order...

 

Following Antonio Tajeda's advice, I got hold of a DS3231 kit to have a play with - more on that later!  I did look up a 900M-T-3CM900M-T-3CM tip for my Hakko FX-888DFX-888D but couldn't find any in the UK and HK Wentworth wanted £20+ and £5 P+P for one which they'd get from Japan.  I'll keep my eye open but decided to try with the tips I had - the T18-D12T18-D12 worked very well.  I also re-watched the videos linked to on YouTube - they make it look VERY easy but I expect technique comes with practice.

 

Following Gene Breniman's and Luis Ortez's advice on a magnifier I have been looking at microscopes but I also tried a head magnifier in the first instance - I got one with swappable glass lenses.  The 2x was great for a bit of through hole soldering I did yesterday, and I managed pretty well on the DS3231 kit with the 3.5 magnification.  My only real issue was having to get so close to see in focus - I was around 4 inches away.  I used a PCB holder and that raised the board up so it wasn't too uncomfortable.  I think I'll persevere with that for a while and save the money.

 

Following Shabaz's advice I got hold of some thin solder - 0.274mm.  It was significantly easier to work with at this size than my 0.46mm.  The two sizes together are great for both through hole and SMD.  I also dropped the temperature down to 300C and had no problems - I suspect with some of the larger pads I should go a bit higher but it all worked.

 

There were a bunch of other tips as well, from many others who I haven't named, in respect to flux, tinning one pad first and so on - these work very well so anyone picking up on this thread could do worse than follow them.

 

Someone, somewhere on a different thread suggested the use of blu-tack (or similar) for through hole - it might have been Shabaz - I can confirm that it is an excellent tip!

 

So, here are some photos.

 

The LED Side

image

 

The other side - mix of SMD and through hole:

image

 

Close ups:

image

 

image

(I honestly thought I'd cleaned that up with IPA - couldn't see the mess by eye!)

 

And, finally:

image

 

As for the kit.  The PCB looks well made, exceptionally 'skiddy' surface.  However there were NO instructions with it which for the most part wasn't a problem, but placing the resistors was really an educated guess - one I got right based on everything lighting up.  There's a couple of dodgy LEDs: in the photo they are lit but will only colour blue.  Also, it isn't possible to actually set a time, date etc as the touch buttons (which I didn't have to do anything with) don't work.  As there's no schematic I can't tell if it's a soldering problem with one of the chips or just a dodgy board: there are no bridges that I can spot under my x5 magnifying glass.  Perhaps the buttons need the battery, who knows??

 

I think there is some scope here for Element 14 to create some quality practice kits, with instructions and troubleshooting hints.

 

Anyway, it was enjoyable doing it and great practice.  Given that it's my fourth or fifth time picking up a soldering iron I'm really pleased with myself.  Time for a celebratory beer.

Parents

  • Hi Andrew,

     

    Wow, that's a world of difference. It looked like a manufactured board, it needs very close inspection to see that it is hand-soldered!

    Regarding flux and cleaning it, that's not always easy, so it can be left on, but I fully understand the desire to visually remove it : ) When working with SMD, sometimes I'll use a flux pen (i.e. very liquid flux) on pads depending on the state of the PCB and parts. For ICs, the thicker syringe flux is great to ensure no bridges, I only use a bit, to reduce the clean-up later. For the cleanup, a really handy tool is a very stiff brush stiff brush (it's a good price currently, it used to be twice that cost. It is very stiff unlike the ones from amazon/ebay), and can be used with your existing IPA. For final wipe-up and getting that spotless look, MG Chemicals IPA wipes are nice but expensive here (maybe cheaper in the US since they are manufactured there). This is lower-cost, heavily soaked, and large so a single sheet could be cut and used for a 2-stage cleaning on a single PCB : ):

    https://www.somersetsolders.com/qualitek-stencil-wipes-pack/p57   postage is high : (

     

    I find LEDs amongst the hardest SMD parts, because if they are not totally square to each other, or not soldered completely flat to the board, then they visibly look wrong. That's not the case here, they look very neatly done.

    It's possible the few LEDs could have been damaged from the supplier (that's sometimes the case with bulk LEDs from ebay etc), or even ESD related stuff during their packaging, or afterwards during un-packing and soldering.

    By coincidence I've been spending today writing up "practical ESD tips" : ) for a project I wanted non-elec-engineers to be able to assemble. You're likely aware of all of this stuff, or better tips, if you're working in production environments.

    Here's the draft, it is incomplete and I'll type it up in a blog post at some later date once I've refined it, and tried to test some of this. This isn't production-grade, just practical/easy tips when dealing with the environment and equipment that exists outside real engineering labs or production environments. Some bits here could be wrong or simplified (don't want to scare off non-elec-engineers either), so I'm still working through it (ordinarily I wouldn't type it without at least experimenting first, but I thought it could be handy since not all the info here is unreasonable):

     

    Practical Electro-Static Discharge (ESD) Ideas

    The semiconductor devices can be damaged by high voltage, such as that generated by insulators rubbing, and carried by the (conductive) human body. To reduce the risk, before you start work, touch an earth point for a few seconds, if no ESD wrist strap is available. This doesn’t eliminate the risk entirely, so an ESD wrist strap is recommended.

     

    Avoid wearing clothes containing silk, nylon, polyester. Remove leather jackets, pullovers/jumpers and any scarves. If ESD-safe clothing is not available, then aim to wear cotton. If the floor is carpeted, then take particular care not to walk too much once you’ve started working.

     

    Avoid working in a very dry environment too. It doesn’t need to be unbearably humid – just a normal level of humidity (40-60%) is fine. You can control that by closing or opening windows.

     

    Ideally the work surface should also be slightly conductive to prevent static charges collecting on parts of it, and it should grounded (via a 1 Mohm resistor). If this isn’t possible, then try to reduce charge on a surface by making the surface conductive (e.g. place a sheet of aluminium on top and not moving it) and then charge can be overall balanced between the sheet and the table top, by touching the aluminium using a wire to an earth point briefly if a permanent connection via 1 Mohm resistor is not possible. If using this aluminium sheet method, then place thick paper card on top so that you’re not working on a very conductive surface. If no slightly conductive surface is available, then consider using a conductive brush to neutralise charge by holding it and wiping the surface slowly, and then repeating at a few millimetres away from the surface, to eliminate friction. A record cleaning brush can be used if it is anti-static. Them, place thick paper card on top to become the work surface. A wood surface, or working on a wooden table is an excellent choice too, but if it is varnished (or even otherwise) use the technique mentioned above to reduce charge on the surface.

     

    Avoid plastic containers and bags being in your work area, unless they are indicated to be conductive or ESD safe.

     

    Once you have started work, try not to dramatically change positions such as sitting and then standing, since the change in height can cause charge to be capacitively coupled.

     

    When handling semiconductors, avoid removing them from their ESD packaging until you’re ready to solder the component in.

     

    Follow the component placement order as closely as possible, since it is designed to populate resistors onto the circuit board first. This acts as a sort of limited protection for the subsequent semiconductors.

  • in reply to shabaz

    Hi Shabaz,

     

    I found these lint free papers on Amazon that could be used if you already have IPA https://www.amazon.co.uk/KLS-Anti-static-Lint-free-Wipes-10x10cm/dp/B017OPM3CQ/ref=sr_1_21?crid=1ZCMOXLD2XCKH&keywords=l…  .  I've not bought them yet as I also found these from CPC which were in stock when I added to my basket, and out of stock when I bought them - they may or may not be back in stock on the 5th June -  https://cpc.farnell.com/electrolube/sti200/lint-free-paper-wipe-saftiss-200pk/dp/SASTI200   Anyway, they're a reasonable price if you already have IPA: they are also available on Amazon at a slightly higher price.  Either of these in conjunction with the brush you mentioned should work well for cleaning.

     

    A

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