Author Topic: solder paste not "sticking" to pcb  (Read 2563 times)

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Offline Simon

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solder paste not "sticking" to pcb
« on: May 06, 2014, 01:43:56 pm »
Well i bought a tube of solder paste and eventually some bog bloges later had a soldered board. Bit what I did find was that the paste did not exactly want to stick to me PCB it was a job to "leave some behind" on the pads. Should I have put flux on the board first ?
 

Offline Codemonkey

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Re: solder paste not "sticking" to pcb
« Reply #1 on: May 06, 2014, 02:03:49 pm »
Had you just taken it out of the fridge ? If its a bit cold its not so easy to work with. To be honest, I avoid using it unless I have a paste mask to screen print it on with, I find normal solder easier to work with. I imagine adding more flux will result in it just spreading out all over the board once deposited.
 

Offline Simon

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Re: solder paste not "sticking" to pcb
« Reply #2 on: May 06, 2014, 02:28:57 pm »
it had been out a little while but then I have no idea how ling it takes a lump of solder like that to come to temperature, I suppose the plastic syringe acts as a thermal insulator.
 

Offline geo_leeman

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Re: solder paste not "sticking" to pcb
« Reply #3 on: May 06, 2014, 03:17:29 pm »
Seems that at mine works pretty decent after about an hour out at room temperature. 
 

Offline MacAttak

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Re: solder paste not "sticking" to pcb
« Reply #4 on: May 07, 2014, 12:35:39 am »
The good thing is that you don't need to get the paste perfectly on the pads when dabbing it on from the syringe. When it reflows it will push away from the soldermasked areas and pool on the pads naturally (exactly where you want it).

I've done a few chips where the pin pitch was to small to cleanly apply paste, or where device disassembly was such a PITA that I chose to solder the board while it was still installed (making it very hard to get close to the board while applying solder). In those cases, I just cleaned the pads and mask well with IPA and then dragged a thin line of paste across the line of pads. Reflowed with hot air and the solder pools itself to the right places and pulls the chip right into place.
 

Offline Simon

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Re: solder paste not "sticking" to pcb
« Reply #5 on: May 07, 2014, 09:43:27 am »
in fact on my first board you could not see the solder mask for the solder but it all went where it was supposed to like you say. Although some parts did not solder quite straight die to the sheer quantity of solder.
 


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