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Soldering Beam Lead Diodes

From the hp_agilent_equipment newsgroup:

I have been messing around with RF+Microwave stuff for over 27years now, I been on both sides of the fence - hobbyist and professional, right now I'm both :)

Usually if you go by the book there are three ways to properly mount beam lead devices:

  • Thermocompression bonding (try this on softboard, good luck :) )
  • Conductive Epoxy (works great, use dispenser and proper size needle)
  • Resistance welding (works great for softboard)

Soldering is considered a bad thing to do and most companies don't even mention the word in their app notes, the problem is that the leads on the diodes are consisting of gold, regular solder has the habit of having a affinity for gold so in other words it will dissolve the gold from your leads, every one who ever tried to repair a hairline crack on a hybrid microwave circuits knows this out of painful experience!

The other issue is that the uneven heating of the diode will cause cracks caused by thermal stress and the flux doesn't have a good influence on the diode either!

So if we want to solder those buggers we got to do it in a proper way:

First off we need a solder that doesn't dissolve our leads, and actually there is such a animal, many suppliers offer solder that contains silver or gold traces for hybrid repair this solder is available in wire or paste form however it is not cheap!

Second we need a way to avoid thermal stress, the best way to do so is hot air!

So the first thing we do is to put small dots of silver filled solder paste on the mounting pads of our PCB , then place the beam lead under the microscope, next we pick a hot air nozzle that's bigger than the diode, set the hot air temperature slightly above the melting point of our solder, hold the hot air pencil above our diode and turn it on until the solder starts to melt, turn the hot air off, let the board cool down and inspect the joints, then clean the flux off the joints using alcohol !

I have soldered many beam leads that way and 99% of them performed well for years to come.


test_equipment/soldering_beam_lead_diodes.txt · Last modified: 2013/01/08 19:00 (external edit)
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