# Why solder paste is not popular and seems almost illegal? [closed]

Once I found out you can use solder paste to assembly at home I was shocked. Think about it, any hardware startup build a pcb, its cheap, then you get it and you want 5-10 copies, and you also have some parts that you can't assembly. What you do ? you go to assembly house. This will cost you between 300 -500$for just 5-10 boards (stencil+assembly). If you have multiple iterations its expensive. In my opinion its a big deal . You can solve all of that and even make 100 pieces at home using stencil. So why it seems people are hiding this ? 1. After hours in Mouser, seems that you can barely find a single product that can actually being shipped, the very few that are in there has 0 stock. 2. There is a lack of information and you can only find a few examples online. 3. There is almost no legitimate store that sells them, only from China. What am I missing ? why is this not a huge big deal in the hardware world ? • Well, the fact you didn't know about it doesn't mean the others didn't... – Eugene Sh. Apr 26 '17 at 15:22 • I started stenciling solder paste onto boards for prototypes at home at least 10 years ago. Little dedicated toaster-oven for reflow. You just need to shop at the right places. The PCB fabs which cater to the small-batch/prototype market which I've used all seem to sell a number of different kinds of paste (leaded/lead-free, no-clean, etc) and either make the stencils or have a link to someone who does. – brhans Apr 26 '17 at 15:26 • It has a shelf life, that means if your a distributor if you don't sell it, you can't sell it. It also needs to be refrigerated. And it's not 300$, you can get it with a reasonable amount for 30 to 60 USD – Voltage Spike Apr 26 '17 at 15:28
• Ah, digikey are better: 50g paste, good old fashioned fully leaded, for £10 digikey.co.uk/product-detail/en/chip-quik-inc/SMD291AX50T3/… – pjc50 Apr 26 '17 at 16:08
• I'm confused. I don't think there's a big conspiracy. I just bought a nice little container of solder paste from Digikey. It even came with it's own adorable cold pack. Edit: pjc50 beat me to it. – uint128_t Apr 26 '17 at 16:08

I have used solder paste (for small one offs at work, rather than at home).

My first thoughts looking at your question is basically that you CAN do SMT solder paste at home. No one is stopping you at all.

As some of the people have mentioned in the comments, Mouser doesn't do solder paste for the shelf life and other issues. I think you are just looking in the wrong place, lots of places have lots of types of solder paste available the only "illegal" part of it is getting solder paste with lead in it, but that's fine as long as you're not trying to re-sell your boards.

Reflow ovens are readily available from many sites (including Farnell and Mouser) and can be got second hand for not much money.

The only other item you need is the stencil, which you can either manufacture yourself or get as part of your PCB creation. Both of which are pretty straight forward, ask you PCB manufacturer or do a quick google and make your own appropriate stencil that way.

I found that the hardest part of doing reflow soldering using solder paste is having a steady hand and good enough eyes to put all the components on the PCBs in the right place accurately enough.

TL:DR; it is a common task to do, sounds like you're looking the wrong place for the paste.

There is another option: skilled technicians can quite happily do SMT assembly without the need for stencils or paste. This might be a good option for doing small runs, although I think getting under $300 might be hard. The companies that do this professionally normally advertise their ability to do board rework - that is, removal, resoldering and trace cutting/patching on already assembled boards. But if you find a nice small company they'll do all sorts of work for an hourly fee. We used to do this for prototypes. Could get 3 FPGA-on-PCIe-card boards done for about$1000, which was cheaper and certainly much quicker than the automated assembly would have been for such a small run.

(Do not underestimate the importance of turnaround time!)

It is not as easy as just using a stencil to "draw" interconnects on a board with solder paste. Hand production will result in high variation in interconnect width, resistivity and quality. Secondly, there is precise thermal processing required to properly flow and set the solder minus the flux. Lastly, there is the lead issue [Sn-Pb] of toxicity for cheap solder pastes used in garage or back room sweat shops. Not an easy process to master for the production of a few boards. Do your homework before messing around with solder. ;o

• Ummm - your answer doesn't make sense to me. Solder paste isn't used to 'draw interconnects'. It's not a replacement for the copper traces on a PCB. It's for soldering SMD parts to a PCB. – brhans Apr 26 '17 at 15:31
• Right, you are thinking about pre-printed copper on PCB; my mistake. Im a new user and edited by comment but do not know where is is posted. – fab_rat Apr 26 '17 at 19:41