How do you do a visual inspection (if any) before P&P and reflow? - Page 1
Forum section: electronics / general

author: olkipukki
author_rank: Frequent Contributor
timestamp: February 18, 2017, 03:44:07 pm
content: Recently, I wasted a bit (not really, a lot actually) time trying to fix that been missed before P&P and reflow. Basically, some parts/pins are not fully covered by a paste (let's say an user error)... Well, this is not big issue on a board with big and bulky stuff, but a few dozes aka 0402 parts that spread around here and there on a panel, not easy to see straight away.Wonder how are you doing an inspection (if any)?As number of parts and their size are going opposite directions for upcoming projects, it will only hard to notice similar issues in the future.I was thinking how to sort it out and come up with (stupid?) idea - compare PCB images before and after a stencil workIn short,1) take picture of PCB as is2) apply a paste on (1) PCB3) take another picture4) we have an sample and expected result5) do same as (2) and (3) for another PCB6) compare (4) and (5) results7) is okay or not?Yes, programming is required (opencv or similar), but not a rocket science...

author: elecman14
author_rank: Unknown
timestamp: February 19, 2017, 02:15:24 pm
content: Quote from: olkipukki on February 18, 2017, 03:44:07 pmYour optimism about how simple this problem is, concerns me. Pre-reflow automated inspection equipment exists. The units I have demoed are much more complex than what you are purposing that do not work all that well (in my opinion). Before you go down this rabbit hole you may want to look at how other companies have solved the problem by getting demo units or going to Productronica or something similar.Implementing it yourself seems to be a tall order. All the ones I have demoed seem to have a large emphasis on consistent lighting. Reflection off un-pasted un-populated pads also seemed to be an issue. Typically it is not as simple as training to a single un-populated model. For example if your IC changes date codes the "model" will change since the IC will have different writing on it. This means that you need to train areas of interest and keep out areas. You also have to consider what happens if a panel fails inspection. Does the convener stop, do you somehow mark it as rejected and reflow it then throw it out, etc.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 20, 2017, 09:14:53 am
content: Having said that I think there is mileage in a camera-assisted manual method - Simple setup (RasPi?) that can take an image of a reference PCB, then place board in same position (jig) and display alternating images from the camera and the reference image. The human brain is very good at spotting patterns and changes.

author: Smallsmt
author_rank: Frequent Contributor
timestamp: February 20, 2017, 12:50:09 pm
content: The main problem is paste change it's style after some time applied to the PCB.So paste inspection should be done directly after printing.For the PNP process the machine can handle if every part is placed well and if needed do a after placement inspection compared to example pictures taken from a good sample.More important is the after soldering inspection. If you want to receive a good result you need to use cameras looking from different angles plus maybe different colored light.We add this feature this year to our new software.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 20, 2017, 02:03:31 pm
content: Quote from: Smallsmt on February 20, 2017, 12:50:09 pmBy far and away the most important factor in minimising rework is a good paste print.If you do have issues with placement, inspecting before reflow will save a lot of time later as it's much easier ot nudge parts around before they're soldered.