Editing / Cutting up a Gerber paste mask for segmented stencils possible? - Page 1
Forum section: electronics / general

author: smoothVTer
author_rank: Regular Contributor
timestamp: August 08, 2024, 06:31:58 pm
content: Hey everyone!I have a rather large ( 12" x 16" ) PCB that I need to assemble by hand. There are approximately 1100 components on the board. In order to be able to assemble this by hand in a reasonable manner, I need to apply paste section by section ( probably 4 total ), reflow them, and then move on to the next section. I've designed in locating holes with studs to affix the stencils in place with NPTH's and matching locating apertures on my stencils.In order to make this work I have to take the entire paste mask gerber file and cut it up into multiple stencils.Does Altium have the capability to cut up the global paste mask/gerber into several sections? Something with camtastic?Are there any tutorials like this already out there? ( I've scanned YouTube but could not find much )Do these sub-stencils have to be rectangular? Can stencils be anything other than rectangles ( no frame needed ) generally?If not, does anyone have suggestions for making multiple sub-gerbers, each with their out outline, out of a single gerber paste mask?Thanks a ton everyone.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 08, 2024, 08:04:08 pm
content: How is it supposed to work if you have a stencil for only a part of a big panel? That would result in moving things around while a part of your panel is wet and sticky, and it becomes very easy to smear the first half of the paste around when you do the rest. Have you thought of that? Another complication is that stencils are much bigger then the PCB. (Especially framed stencils) The "extra size" is often arbitrary or some standard distance (5cm?) Maybe you can order a specified size for the outside of the stencil too, but it may be thin enough to cut with a strong set of scissors (or metal cutting pliers if you have those) But it's all to easy to deform the stencil while attempting to do so yourself.For the rest. Gerber editors do exist. I think there is something called Fab 2000 that can do such things.Another option is to make a copy of your project, then delete big sections of the panel, and then create new gerbers for just a section of the big PCB for ordering the stencil.

author: thm_w
author_rank: Super Contributor
timestamp: August 08, 2024, 09:05:36 pm
content: Quote from: Doctorandus_P on August 08, 2024, 08:04:08 pmThey said they would reflow the panel in between placements.Depending on the components this might not be a good idea either.OP: what parts are on this board, 1100 LEDs? or a mix of stuff.

author: Accu-Sembly
author_rank: Contributor
timestamp: August 08, 2024, 11:32:01 pm
content: We use GC-PreviewPlus here to edit Gerber layers, but we are only an assembly house and don't do design work.We have, however, had to chop up a stencil into multiple sections. In our case it was because the client had a heatsink built into and epoxied directly to the bare board with multiple areas in and around that needed to be pasted. It can be done, but it will be a pain. Our stencil house had to make a series of mini stencils as well as a full size one with all the individual sections removed. The mini stencils just have the sheet metal turned upward on one side for you to hold it and we even ordered custom sized squeegee blades that fit exact to hand paste the much smaller zones.Definitely don't recommend it if it can at all be avoided. Certain components / manufacturers will list a specific number of recommended reflow cycles and it sounds like you'll be doing several. Plus, the flux has been activated and consumed during each reflow pass, so sending that first zone to liquidus multiple times might create defects.

author: smoothVTer
author_rank: Regular Contributor
timestamp: August 09, 2024, 06:43:50 pm
content: It will be a mix of components, yes, everything from 0603's to IC's of various types to MOSFETs of various package sizes, one large pitch BGA component ( 0.65mm )I've tried in the past cutting up a single stencil into multiple sub stencils, but as user mentioned above, it deforms the stencil pretty badly and not a good experience.I do understand about defects on these boards from multiple reflow cycles is a possibililty. However with a total of 5 boards that will be used in-house only, the external exposure to people outside the company is not an issue. I will have to live with the possibility of having to debug something that may have a defect and replacing it. In my experience working with a similar board used in a similar setting here, I haven't had any issues reflowing or reworking sections of this PCB.Thanks for the suggestions everyone.

author: tooki
author_rank: Super Contributor
timestamp: August 09, 2024, 07:07:43 pm
content: Quote from: smoothVTer on August 08, 2024, 06:31:58 pmWhile I concur that this approach is fraught with peril (I did it once for a much smaller PCB than yours, and quickly came to regret it), here’s how you do it:Duplicate your PCB’s .pcbdoc file enough times so that in addition to the original file, you have one copy for each stencil section.Open each stencil section .pcbdoc and delete all the components outside of that stencil section. Repeat for each section. Generate Gerbers for all of these.When ordering the PCB and stencils, upload the Gerbers for the PCB, but do not order a stencil for it. Then you order a stencil only (but no PCBs) for each stencil segment.

author: Accu-Sembly
author_rank: Contributor
timestamp: August 09, 2024, 07:52:32 pm
content: Do you not have the equipment available to populate and reflow all at once?You can get stencils in miniframes to help with storage and rigidity. See attached photo.Quote from: smoothVTer on August 09, 2024, 06:43:50 pm

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 09, 2024, 09:38:21 pm
content: What about making several smaller PCB the "normal way" and add some connectors and a frame?Maybe you can overlap the PCB's with each other If you then use THT "connector footprints" the PCB's can be soldered together by just putting in a simple one (or double) row header(s).If the PCB's have to be in the same plane, then a gap in between, fingers on the edge as in with edge connectors, and you can solder single row headers over it to connect the PCB's together.