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Maximum Solder Paste Wait Time — Parallax Forums

Maximum Solder Paste Wait Time

sunblocksunblock Posts: 55
edited 2013-01-06 12:05 in General Discussion
Does anyone know if there is a maximum time between the point where solder paste (and SMD components) are placed on the PCB and when the PCB must be put through the baking process? In otherwords, if I want to put half of the SMDs down tonight and wait until tomorrow to do the rest before baking will there be a problem? Solder paste is QuikChip brand SMD291AX.

Comments

  • FranklinFranklin Posts: 4,747
    edited 2013-01-04 19:12
    I don't think you will have a problem as long as the parts don't fall off (unlikely)
  • SRLMSRLM Posts: 5,045
    edited 2013-01-04 19:19
    The longest I've done is about 2 hours total. Any longer and I'd be afraid that the paste would start to dry, but I don't know. Why don't you give it a shot and let us know? I'm interested to see if it works.
  • LeonLeon Posts: 7,620
    edited 2013-01-05 01:57
    Ask Quik Chip?
  • sunblocksunblock Posts: 55
    edited 2013-01-05 09:18
    How about an answer?
    I called quik chip before i wrote this post and they pointed me here...
    http://www.digikey.com/product-search/EN?mpart=SMD291AX&vendor=315
  • TtailspinTtailspin Posts: 1,326
    edited 2013-01-05 09:30
    I guess, if your just talking about overnight, why not put the circuit board in the fridge?
  • LeonLeon Posts: 7,620
    edited 2013-01-05 09:48
    sunblock wrote: »
    How about an answer?
    I called quik chip before i wrote this post and they pointed me here...
    http://www.digikey.com/product-search/EN?mpart=SMD291AX&vendor=315

    Ask them again?
  • RDL2004RDL2004 Posts: 2,554
    edited 2013-01-05 12:14
    I would doubt there are any significant amounts of room temperature volatiles or oxidizing materials in any solder paste. It's probably good for days, if not weeks.
  • WBA ConsultingWBA Consulting Posts: 2,934
    edited 2013-01-06 02:17
    First, Chip Quik should have sent you to the Amtech's web page for the Syntech paste that has a link to a clean data sheet (since they actually make the stuff), rather than a link to a distributor that has a corrupt data sheet on their site (the one I downloaded from Digikey has several sections that came up with junk characters).

    Anyhow, what you are looking for is "tack time" and the Amtech Syntech datasheet sadly avoids declaring this. However, the web page for the paste states:

    wider process windows (12-18 hour stencil life, 18-24 hour tack time)

    A tack time of 18-24 hours is rather long for solderpaste, so I would have to see it to believe it personally (but I also have not used pastes with synthetic flux materials). Kester EP256 is rated at "8+ Hr Tack Time" which is much more common with no-clean, tin-lead pastes. Basically any paste begins drying out after about ~4 hours. Once that begins, the performance of the flux begins to deteriorate, thus reducing the quality of your reflow process. You may be able to gain some time by placing the pasted board in a fridge in an airtight container to prolong the paste life.
  • sunblocksunblock Posts: 55
    edited 2013-01-06 07:54
    Thank you... Very much appreciated
  • Mark_TMark_T Posts: 1,981
    edited 2013-01-06 12:05
    Ttailspin wrote: »
    I guess, if your just talking about overnight, why not put the circuit board in the fridge?

    Because putting anything giving off solvent fumes in a fridge should set alarm-bells ringing.... Door switch = spark, solvent = explosive atmosphere.
    They did this as a safety demo for graduates - by blowing up a fridge. Classic example is ether, still highly volatile at -50C...

    For one small board its not an issue due to the small amount of solder paste, but done on a larger scale could be extremely dangerous.
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