My First SSOP28 - Page 1
Forum section: electronics / beginners

author: sonicj
author_rank: Frequent Contributor
timestamp: September 08, 2010, 07:09:34 am
content: Hey all! I just soldered my first SSOP28 and thought I would share some pics for evaluation / discussion. Its not perfect, but I think it should be fine for personal use. I have reworked this pitch before, but never mounted a fresh chip & board. Despite the bit of twist, I was expecting a lot more difficulty with the whole process. I'm not sure how that one side got so far shifted off the pads... i tacked opposing corners thinking everything was square, but apparently it shifted a bit at some point. Rather than try to fix it and risk damage to my nice new chip, i fought against my OCD urges and decided just to leave it and proceeded with the rest of the pins. i used a 700° chisel that was almost exactly 2 pins wide. i tinned the tip, then touched 2 pins, re-tinned, touched 2 pins etc. bridges weren't even a concern once i got going!i think the rough texture might be from alloy incompatibilities? i have the feeling the solder i've been using is garbage... it this 60/40 that came from a hamfest my dad went to like 7 years ago. im guessing it was probably old stock before he bought it! (i didn't realize solder went bad until a few days ago) ordered up some kester 44 + pb-free 48 & k100ld to see what this lead free thing is all about.anywho, SMD is a LOT less scary than it was a few hours ago!comments, criticism, advise, feedback, etc. is much appreciated! cheers!-sj

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 08, 2010, 09:00:25 am
content: Forget leadfree.The best solder is leaded with 2% silver.And if you don't have a flux pen, get one.

author: Varal
author_rank: Contributor
timestamp: September 08, 2010, 10:41:43 am
content: Nicely doneYou'll have to pay more attention to the rotation of the chip though - if the pitch were smaller you could have made bridges or even solder the wrong pin to the wrong padBelow is a tutorial on SMD soldering which I've found very usefull in my first attempts (especially the part about QFP and later)

author: Simon
author_rank: Unknown
timestamp: September 08, 2010, 11:57:12 am
content: presumably this is a 0.05" pitch ? nice, I used to be horrified at the prospect but now that making PCB's is becoming the norm for me and having to use SMD/SOIC part because that's the only package they're sold in I've bitten the bullet done a couple and would happily convert to SMD parts any time.

author: allanw
author_rank: Frequent Contributor
timestamp: September 08, 2010, 12:11:04 pm
content: It helps to use a lot of flux.

author: sonicj
author_rank: Frequent Contributor
timestamp: September 08, 2010, 12:38:40 pm
content: Quote from: mikeselectricstuff on September 08, 2010, 09:00:25 amis the silver compatible with components & boards that have been tinned with pb-free? no pen yet, but i do have a syringe full of paste thats difficult to clean up. is the pen still needed if i have paste?Quote from: Varal on September 08, 2010, 10:41:43 amthanx!seen it! i've seen all his videos! hes who i ordered the kester from!Quote from: Simon on September 08, 2010, 11:57:12 am0.026"i think it'll be a good while before i need to solder anything smaller pitch than this. im hooked on the smd stuff now, i just wish i could diy the boards!Quote from: allanw on September 08, 2010, 12:11:04 pmyes. i don't know how i soldered anything before i got this tube of flux!cheers!-sj

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 08, 2010, 12:56:01 pm
content: Quote from: sonicj on September 08, 2010, 12:38:40 pmSeperate flux is always useful, for pretty much any soldering task, SM or otherwise.You can never have too much (fresh) flux.A good example is for cleaning up messy/rough joints - just coat with flux and touch the iron on join. With a wide blade biit you can clean up a whole side of a SO or QFP in one go, and wiiill often clear shiiiirted pins at the same time.Solder with silver is compatible with everything, LF or otherwise. It is particularly reccommended for chip parts with silver terminations, as normal solder sucks the silver out, however I'm not sure how common these are nowadays.It has a lower melting point than 60/40 - lower temps are always a good thing.If you really must use leadfree, the LF stuff with silver is much nicer to work with, again it lowers the melting point.

author: DJPhil
author_rank: Frequent Contributor
timestamp: September 08, 2010, 01:07:29 pm
content: Quote from: sonicj on September 08, 2010, 12:38:40 pmSome parts are pre-tinned with solder that has a small amount of silver (check datasheet, it's usually mentioned somewhere out of the way) and using a similar solder to populate it will help avoid migration of silver out of the joint, making it brittle. Opinions differ on the level of concern a hobbyist should feel about this, but if you've got at least a little 2% silver solder handy you can use it when the datasheet for a part mentions it. More details at the Kester link below.I'd definitely recommend you try a flux pen if you're used to paste, it's a world of difference. I've got a Kester #186 that's lasted quite a while, you'd be surprised how long you can make 10mL last! The pens distribute flux as a runny liquid so they can be messy until you get used to them, but unless you're a master with a toothpick and a tube of paste flux it'll be a welcome change.Some resources of note:Kester's site- They've gone to the trouble to make a good FAQ and knowledge base (under tech support). Great quick reference material!IPC Media Portal- This is where the IPC (basically a PCB design/manufacture standards body) keeps full length demos of their industrial soldering training videos. Highly recommended if you have the time.Hope that helps.

author: Unknown
author_rank: Unknown
timestamp: September 08, 2010, 01:18:29 pm
content: I don't think there's an issue with soldering lead-free PCBs and parts with lead. I have received notices with lead-free soldered kits (SMD parts are pre-soldered so those poor hobbyists don't have to) that adding even a tiny amount leaded solder to the lead-free joints would make them brittle and less reliable. Not sure what the ratios are, I've always assumed that it's not a big deal if it's 95% leaded solder and 5% lead-free solder (pre-tinned leads and PCB), so I've always cleaned them up with solder wick if I had to reflow/replace them, but haven't done much research.Quote from: mikeselectricstuff on September 08, 2010, 12:56:01 pmNot very I believe.Quote from: mikeselectricstuff on September 08, 2010, 12:56:01 pmSn60Pb40 is 183-190?C according to Kester. Sn62Pb36Ag02 is 179-189?C. Sn63Pb37 is 183?C. 63/37 is actually lower than silver-bearing, and the difference between 60/40 and 62/36/2 is not really enough to matter in my opinion. I find euctic (no plastic stage) a much more useful property. It does appear to be correct for lead-free solutions.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 08, 2010, 02:45:44 pm
content: QuoteI never really looked into why the 2% silver was better - just noticed that it produces nicer shinier joints more easly!

author: Unknown
author_rank: Unknown
timestamp: September 08, 2010, 03:09:42 pm
content: Sure, silver is shiny, no argument against that.

author: saturation
author_rank: Super Contributor
timestamp: September 08, 2010, 03:14:35 pm
content: Good job. Far better than a lot of made-in-china electronics products I've seen!

author: Unknown
author_rank: Unknown
timestamp: September 08, 2010, 06:46:18 pm
content: One of the issues of lead-free is that it looks ugly, even if it's a good joint. They never look as nice and shiny as with leaded solder.

author: orbiter
author_rank: Frequent Contributor
timestamp: September 09, 2010, 08:29:11 pm
content: Right! I'm off to eBay to order some leaded solderI've been using LF since buying a load of it a while back, however I'm getting fed up with my joints (not MY joints) getting to around nine million degrees C then looking terrible when finished.

author: sonicj
author_rank: Frequent Contributor
timestamp: October 14, 2010, 12:14:06 am
content: the results are in.... lead free sucks!i didn't even try to solder any surface mount stuff with the pb free as i had pretty miserable results with my preliminary attempts with various awg wires. my results with kester's k100ld looked nothing like their example photos and took quite a bit of effort to produce joints i was reasonably satisfied with. ROHS is hippie idealism bull$h!t imo! good luck finding any of today's electronicsstill functioning 30 years from now.anywho... heres some pics of my latest attempts! the first picture isSn62Pb36Ag02 from Radio Shack, which imo, is pretty good stuff! 1oz of .015" is around $6 and lasts a good while if you aren't doing heavy utility type stuff. kester Sn62Pb36Ag02 is relatively difficult to find, especially in quantities less than 1lb.the other two chips were soldered with Sn63Pb37 fromcurious inventor. $2.50 per 1oz roll. i really like this solder! the flux seems to be a little more activated than the silver bearing, but could have been due to the thickness of the solder.all three were soldered with a weller wesd51 equipped with the stock 1/16 screwdriver tip. temp was set 650°F. the larger max4550 was soldered with the help of amtech rma-233-uv (nasty fumes. difficult to clean. great wetting though!) the smaller max7456 was aided by kester 2331-zx water soluble. the 2331-zx seems to leave behind a powdery residue after cleaning with alcohol. this sometimes takes a lot of scrubbing to remove!not sure why the solder mask is different on the two 28 pin boards.... didn't seem to make much of a difference soldering. i didn't even notice until i started taking the pictures.cheers!-sj

author: TheDirty
author_rank: Frequent Contributor
timestamp: October 14, 2010, 02:59:46 am
content: Good work..5mm is going to be a little bit harder, but obviously not unmanageable now that you found your stride with it. Really this opens up so much now, since so many chips don't offer DIP anymore.This takes me back. This was my first 28 lead soic.

author: Unknown
author_rank: Unknown
timestamp: October 15, 2010, 10:33:48 am
content: Quote from: sonicj on October 14, 2010, 12:14:06 amWhat a surprise, water soluble flux is not dissolved by alcohol. How about using water if you must use water soluble flux instead of R(M)A or no-clean?