From: nospam@no-address.com   
      
   On 20.05.2018 05:06, Ray Otwell wrote:   
   > From time to time I have wondered if a very narrow tip could be used   
   > for the larger SMT items.  I've seen tutorials on how to do the SOP   
   > and SSOP packages with larger tips..  It doesn't look easy at all,   
   > but doable.  ...   
      
   In principle, both ways are possible. You might be surprised how small   
   those narrow tips can be made.   
      
   Weller makes one called the "LT 1S" - it's 0.2 mm (<8 mil) round tip.   
      
   I've used it a while ago, it works reasonably well (*). With some care   
   and dexterity it can even fit between the pins of a 0.5 mm pitch TQFP   
   to remove an accidental solder bridge. It should however be considered   
   a precision tool and treated accordingly - avoid application of force,   
   overly high temperature (below 370 °C is reasonable) and make sure that   
   it's maintained wetted at all times to prevent surface oxidation.   
      
   This type of fine tip does not tolerate abuse at all well.   
      
   There are special-purpose tips with even smaller dimensions. A Weller   
   "LT 1SCNW" has a 0.1 x 0.3 mm rectangular tip geometry, but it's not   
   designed for general-purpose soldering use. It's non-wettable, so you   
   can't actually apply solder to it. It can only heat up an already tinned   
   area and melt the solder that's already present there. It may (or may   
   not) be useful to clean up a mistake with a 0.4 mm pitch TQFP, I don't   
   really know. So far I've been lucky and never needed one.   
      
   It is quite possible to solder a part in a 0.5 mm TQFP100 package with a   
   "LT 1S" tip, working carefully pin by pin. If you made a layout mistake   
   and created a very tiny pad geometry where the pads do not extend enough   
   outward past the pins, and the traditional large flat tip sweeping all   
   pins approach will no longer work, this may be the only remaining way.   
   Be warned however that it's really labor-intensive, prone to mistakes,   
   and requires great care.   
      
   If the pad geometry allows it, working with a larger gull-wing type tip   
   and "drag soldering" a row of pins at once is certainly the far more   
   productive and less frustrating approach, and it places less demand on   
   manual dexterity too.   
      
   Regards   
   Dimitrij   
      
      
   (*): Considering its size and the circumstances where it's likely to be   
   needed, that is.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)