4 ms·

For those of us without the cash/apartment space for a PNP, has anyone experimented with a stencil system for populating passives? Is that even a thing? My PCB

by junon 3mo ago

For those of us without the cash/apartment space for a PNP, has anyone experimented with a stencil system for populating passives? Is that even a thing? My PCB project's population time is currently 11 hours the last time I did it, from blank to tested, for one unit. The largest amount of time spent is on the resistors and capacitors - over 200 of them.

q3k 3mo ago
What? These stencils are just for solder paste placement, you still need to actually place your components some other way before reflowing.
- junon 3mo ago
  I am aware, yes. After the paste deposition via stencil, doing passives manually takes hours. I'm asking if anyone's done anything interesting with stencils for placing those.
Joel_Mckay 3mo ago
In general, most single-sided PCB work with 0.5mm pitch components can be done by hand with a metal stencil + dry-wall trowel edge, SAC305 Type T4 or T5 paste, hot-air rework hand tool, and or a toaster oven re-flow kit (will often smoke flux due to bad temperature profiles.) Getting a PCB mostly factory assembled for you is likely the better choice if you live in a building, as dropping hundreds of 100nF MLCC on a project can be brutal. I guess the answer is yes one can do prototypes by hand if you take design considerations for pad access (sloppy mechanical tolerance for pencil/air rework), but probably one should be spending their time on design for lab EMC/EMI. =3 Robert Feranec does quite a few EE interviews, factory tours, and is generally accurate 97% of the time. https://www.youtube.com/@RobertFeranec/videos https://www.youtube.com/@RobertFeranec/videos
- junon 3mo ago
  I know all of this; assembly of a $400 board usually has a MOQ of 5 off the top of my head, which for a board that is a prototype isn't feasible. I know about how to do reflow. I'm asking about the population step after paste deposition.
  - Joel_Mckay 3mo ago
    Could also keep your design tolerances less tight (QFN>BGA), and use a cheaper PCB fab house. In general, for small discreet components they should be able to partially pre-fill the PCB for under $23/pc. The expensive/sensitive stuff you manually add later. Air-tweezers and a magnifier also do work, but you will get a sore back pretty quickly. There were a few manual-first exceptions I saw with fussy RF component selection (better s parameters if mounted upside-down), instrumentation grade high-precision components, pricey chips, and avoiding BGA x-ray pad inspection. Setting up a small home PnP takes time, practice, and space. Not necessary if you just dropped on 5 chips using generic stencils, and re-flow. =3

by junon 3mo ago

q3k 3mo ago

What? These stencils are just for solder paste placement, you still need to actually place your components some other way before reflowing.

junon 3mo ago
I am aware, yes. After the paste deposition via stencil, doing passives manually takes hours. I'm asking if anyone's done anything interesting with stencils for placing those.

Joel_Mckay 3mo ago

In general, most single-sided PCB work with 0.5mm pitch components can be done by hand with a metal stencil + dry-wall trowel edge, SAC305 Type T4 or T5 paste, hot-air rework hand tool, and or a toaster oven re-flow kit (will often smoke flux due to bad temperature profiles.) Getting a PCB mostly factory assembled for you is likely the better choice if you live in a building, as dropping hundreds of 100nF MLCC on a project can be brutal. I guess the answer is yes one can do prototypes by hand if you take design considerations for pad access (sloppy mechanical tolerance for pencil/air rework), but probably one should be spending their time on design for lab EMC/EMI. =3 Robert Feranec does quite a few EE interviews, factory tours, and is generally accurate 97% of the time. https://www.youtube.com/@RobertFeranec/videos https://www.youtube.com/@RobertFeranec/videos

junon 3mo ago
I know all of this; assembly of a $400 board usually has a MOQ of 5 off the top of my head, which for a board that is a prototype isn't feasible. I know about how to do reflow. I'm asking about the population step after paste deposition.
- Joel_Mckay 3mo ago
  Could also keep your design tolerances less tight (QFN>BGA), and use a cheaper PCB fab house. In general, for small discreet components they should be able to partially pre-fill the PCB for under $23/pc. The expensive/sensitive stuff you manually add later. Air-tweezers and a magnifier also do work, but you will get a sore back pretty quickly. There were a few manual-first exceptions I saw with fussy RF component selection (better s parameters if mounted upside-down), instrumentation grade high-precision components, pricey chips, and avoiding BGA x-ray pad inspection. Setting up a small home PnP takes time, practice, and space. Not necessary if you just dropped on 5 chips using generic stencils, and re-flow. =3