2D/3D SOLDER PASTE INSPECTION NECESSITY OR COMFORT? - Page 1
Forum section: electronics / general

author: VladaAca
author_rank: Contributor
timestamp: April 02, 2021, 08:28:33 pm
content: Hello everybody,I have smd line for small/medium production (200-300 boards monthly). It consist of slow P&P machine (2500cph) , reflow oven with conveyor, and very basic stencil printer (like cheep Chinese ones but well made). I make some boards with small (0402) and fine pitch components (0.5mm) and my basic stencil printer is not up to the task. I look around on the market what is available and first qualitative jump are printers with vertical stencil to board separation. Additional improvement on this platform is guided squeegee, camera for alignment (but still operator do alignment) and motorized drive (motors and/or pneumatic cylinders) of squeegee and separation. Machine size vary from desktop versions to stand alone ones. Next qualitative jump is automatic board to stencil alignment (vision), under stencil cleaning, digital control for all print parameters (printing speed, squeegee pressure, separation speed….) and board and stencil inspection (2D/3D scanning of paste deposition). My focus was on second hand older machines, new ones probably have more sophisticated functions but are out of my price range. These machines are quite huge (1.5x1.5…2m), heavy and complex. And fast. As my p&p are not fast, printing speed is not advantage for me. Automatic alignment is more comfort than necessity (or not?). So, my question is:from the view point ofreliability, whether it is worth investing in a machine that has 2D (3D) paste inspection? Or, like in title, is it necessity or comfort?All suggestions, especially from people who used different printers and can compare results, are welcome.

author: SMTech
author_rank: Frequent Contributor
timestamp: April 03, 2021, 11:17:27 am
content: I would skip the in-between models that leave you doing the alignment and tweaking and go for at least a true semi-auto, something like the PBT "FA23" (aka Essemtec SP150 or the very similar but slightly older SP200). These are smaller than the fully automatic machines but have a lot of their features and come very close to being 100% automatic. This won't get you SPI but at least it will put a controller and repeatable control in charge of all the things that affect your print quality and you are doing by feel with a manual printer. Squeegee Speed,Squeegee Pressure, Snap-off distance, Separation Speed, an underwipe etc.I personally manage a reasonable job with a manual and 0.5mm pitch, but only with proper stencils under decent tension with a nice surface finish, PCBway/JLC give noticeably poorer results.You should be able to get by without SPI if you improve the printing, but if you do choose a 2nd user fully automatic, there are lots of them out there, they are affordable and it would be silly to choose one that didn't have it. Once you move on to BGA etc it gets that much more critical, however I'd make sure I had decent stencil cleaning first.

author: Mangozac
author_rank: Frequent Contributor
timestamp: April 04, 2021, 12:32:33 am
content: We went for a used MPM UP2000 fully automatic printer. It is capable of doing some 2D post print assessment but we don't use that feature and haven't had any issues. We were initially going to use the typical semi-automatic printer from China but I'm so glad we didn't. Not only does the fully automatic printer give us perfect prints every time but a big part of the reason it's able to do that is that it automatically cleans the stencil after a set number of operations (we typically program for 6-8).Ensuring that the underside of the stencil is clean is probably the most important aspect of getting good prints. Not only does it wipe the bottom of the stencil with IPA, but it also has a vacuum mechanism to suck any residue out of the apertures.Now, all of that said, I'm not sure if a fully automatic printer is really cost feasible for just a few hundred boards per month. We're doing several times that quantity. You definitely don't need automatic paste inspection.At the sizes and pitches you mention I would want to go for at the very least camera assisted alignment. You operator will otherwise end up with a very sore back leaning over the printer to check the alignment each time!We use JLC 550x450mm framed stencils and the results are great.