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Which is the best way to solder small components such as SOIC or QFP44 packaged components to a PCB without using adapters?

And how can I manage to print PCBs with small track distances and widths for those type of packages?

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    \$\begingroup\$ I gave up making my own PCBs a long time ago. Places like PCB123 give you the software and have competitive prices. It's worth not having to deal with ferric chloride, ammonium persulphate, and whatever darkroom and hole-plating chemicals are needed, and all that drilling. \$\endgroup\$ – Mike DeSimone Oct 13 '11 at 14:29
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    \$\begingroup\$ This is two separate questions. \$\endgroup\$ – tyblu Oct 13 '11 at 15:14
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Drag-soldering works very well for me. Tack down two opposite corners ensuring that the chip is correctly positioned, apply plenty of jelly flux, put a small blob of solder on a medium tip and drag it along each row of leads. Remove any solder bridges with desoldering braid. I use a mini-hoof cartridge with my Metcal system which is specifically designed for drag-soldering.

I often make my own PCBs at home using the photo-etch process; the UV exposure unit cost me about £20 to make, and I print the transparencies on my HP inkjet printer. I don't have any problems with fine-pitch devices, and can go down to 8/8 mil track/spacing. I normally use 10/10 or 12/12 mil, though.

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  • \$\begingroup\$ Solder bridges mean you used too much solder or had some on the iron tip when you started the drag. And Metcal irons are the best ever. \$\endgroup\$ – Mike DeSimone Oct 13 '11 at 14:26
  • \$\begingroup\$ You need some solder on the tip before starting to drag-solder. Too much can cause bridges. \$\endgroup\$ – Leon Heller Oct 13 '11 at 14:30
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    \$\begingroup\$ +1 I did my first drag soldering for a TQFP100 recently, with 0.5mm pitch. That worked very well with few solder bridges that were easily removed. The only problem I that occurred is a small offset of about 0.1mm on two sides (but luckily no functional problems). Some people recommend to tack down 4 corners to avoid this. I looked at some Youtube videos to see how it is done before I started and used a Weller iron with a small hoof tip. \$\endgroup\$ – starblue Oct 13 '11 at 14:48
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I'd go buy a hot air rework station, like the one reviewed here: http://www.youtube.com/watch?v=vva2t21sOAs

The rework station is an absolute must-have if you plan on doing anything with SMD and you can do a lot of assembly using one.

An IR oven is nice to have if you plan on producing several PCBs, but you can't do rework with one.

Unless you are in a hurry, then forget all about making PCBs yourself, order some from China in stead, it's much higher quality than what you can do yourself and it's really cheap these days.

See this page for a description of what you can expect and a link to the webshop: https://github.com/dren-dk/HAL900/wiki/Quirks-of-PCB-manufacturing-at-ITead

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    \$\begingroup\$ I'd agree if the OP were asking about DFN, QFN, or BGA packages. \$\endgroup\$ – Mike DeSimone Oct 13 '11 at 14:27
  • \$\begingroup\$ @Mike - My thoughts as well. We're talking about SOIC being intimidating for a beginner, not about anything really small or hard-to-heat. \$\endgroup\$ – Kevin Vermeer Oct 13 '11 at 14:30
  • \$\begingroup\$ Well, you are going to need a hot air tool to rework a SOIC, but yes, assembly of SOIC and QFP is easy enough with a normal iron. \$\endgroup\$ – dren.dk Oct 14 '11 at 9:25
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SOIC packages can be soldered with out the need of any special soldering equipment. http://murlidharshenoy.wordpress.com/2009/10/17/diwali-project-led-luminaire/

For finer pitch packages try the Hot plate technique.This blog has good instructions on how to solder Finer pitch packages

http://kennethfinnegan.blogspot.com/2010/12/soldering-goodfet-31.html

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For the soldering of those type of components you either want a Hot Air Rework station (a small hot-air blower that gently blows air at hundreds of degrees C) or, ideally, a reflow oven.

You can make your own Reflow oven from a small Toaster oven, and something to control the temperature. There are many sites on the net where people have documented their attempts.

As for the production of the boards - I wouldn't recommend trying to make your own.

I assume you mean with the toner-transfer method...

Having tried myself and had poor results I wouldn't recommend even bothering to try it.

Firstly, getting the heat just right so the toner transfers well without it blurring and blending with the neighbouring tracks is almost impossible at those distances. Also, you need a very good high resolution laser printer in order to get the detail levels.

Secondly, you really really really require a solder resist mask, which you won't get when you make it yourself. Without that you'll just end up with a homogeneous blob of solder instead of a nicely soldered line of pins.

For TT board production I rarely go below 20/20 (20 mil track width and 20 mil track spacing), and never below 15/15. Even then I sometimes get problems.

Of course, you could always invest in the equipment to do Photo Resist etching - but that's not cheap and only worth it if you're going to do quite a few boards.

Personally I like to use a service called "Go Naked" from Spirit Circuits here in the UK. They will create a professional prototype board for you free of charge, but with no solder mask or ident layers - just the tinned copper tracks. It's pretty good for testing things or making a one-off to try out an idea. It can be a bit of a pain not having the solder mask layer though, and I tend to paint the critical areas with liquid latex (under the name of Multi-Core Solder Resist Mask - price about £10 per 250ml bottle) to make soldering easier.

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  • \$\begingroup\$ SOIC and QFP do not require a rework station or oven. \$\endgroup\$ – Kevin Vermeer Oct 13 '11 at 14:32
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    \$\begingroup\$ No, they don't require it, but they're a whole lot easier with one. \$\endgroup\$ – Majenko Oct 13 '11 at 15:07
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    \$\begingroup\$ Toner transfer has worked well for me. The photolithographic method requires a good photomask which I have found to be difficult to create on my printer. \$\endgroup\$ – Dave.Mech.Eng Dec 8 '11 at 2:09

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