[hpsdr] Solder paste Storage and Use

[John Nordlund]

One other note for storage of solder pastes.

Remember this is a suspension of particles of solder alloy in a flux 
paste.  Even refrigerated, the metallic particles will slowly settle to 
the bottom of the container.  This settling action is the main reason 
for the expiry dates on solder paste.  Physical rotation (turning over) 
of the stored  container will prolong the life of the product by 
allowing the metal to 'settle' back into it's previous locations in the 
tube.  Rotation once a month on refrigerated paste will extend it's 
usable life  almost indefinitely.  For our purposes, the paste can also 
be remixed if it separates somewhat during storage. Remixing is not 
allowed for certified work regulated by agencies like the FAA, but poses 
no operational risk for amateur applications.

For good quality solder joints, be sure to follow the paste 
manufacturers recommendations for soldering temperature.  Use a 
temperature controlled iron.  The flux is designed to become active and 
de-oxidize the joint at a specific temperature range, and hotter is not 
better.  With a controlled iron, you can stay on the joint long enough 
for the heat in the joint to rise to the active temperature of the flux 
and allow a proper solder flow to occur between the solder land and the 
device terminations without overheating and damaging the component.

73 de AD5FU  -  who works in the quality assurance area of an FAA 
regulated electronics manufacturer inspecting SMT solder joints

-------- Original Message --------

***** High Performance Software Defined Radio Discussion List *****

Dominic

Solder paste is available in the UK from a number of sources - Farnell being
one, they will sell to you without a trade account (unlike RS, CPC and some
others that are Trade only).  The 10g syringe will last you literally ages -
probably years and costs £7.30+VAT and delivery, less if you buy multiple
quantites. 

Keep it safe in a fridge to extend the shelf life, and make sure the
kids/cat/dog can't get to it.  Don't worry about the expiry date - for most
home-brew porjects solder paste can be used well past it's shelf life,
especially if kept cool.  

And don't buy the RoHS compliant stuff - theere is a specific exemption in the
RoHS rules that allows projects for home construction to use proper tin-lead
solder.

regards

Grant  G8UBN
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