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From:
"Stadem, Richard D" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D
Date:
Wed, 20 Dec 2017 22:49:38 +0000
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Hi, Bob

I would greatly appreciate a CM who automatically ran this software check for a first time build of prototypes. Here is why:



Part rotation should be checked. It is possible to place a component between one (correct) pad, and the other end on an adjacent unused (no-pop) component's pad. If the adjacent no-pop pad is tied into the same circuit, or even to another branch nearby, it can still function and pass testing, only to fail later during production or LRIP from a shortened life. I have actually seen this happen more than once, and have heard of it happening several other times. It is a sad situation when it begins to show up and you now have 5000 boards in the field.



Wrong footprints happen all the time, for many different reasons. It is a good thing to have a software check that looks at the gerber dimensions in the SMT artwork and verifies them with the part print dimensions in the component library to ensure a good match.



For Part Spacing, it is standard practice to list the minimum electrical spacing requirements on the FAB PWB drawing, along with any exceptions to a general rule such as .006" or .010". You don't need to know what the voltages are, you just need to know what the spacing requirement is, and where the exceptions are, and you plug that into the layout software and it uses that info to perform the virtual check.

Many layout CAD packages can take the minclear spec and check for violations through a virtual check of the part dimensions and the pad artwork, but not all.



Polarity markings are commonly missing in the artwork and are also commonly missed during prototype build and checkout, because without a mark on the PWB, the inspector does not realize the part requires the correct polarity. It goes undetected at test because many caps and even some diodes will allow the circuit to function if backwards. Another example of this is a DIP resister network where each resistance value is the same. Again, during mass production is when the issue becomes manifest, typically because the component is overstressed to premature failure, or the other components in the common circuit fail as a result.



There are a lot of software packages that can check for layout issues such as polarity, spacing, and other issues, but they are typically an integral part of the design software itself. There are other independent software packages that can check for these things, but I have not had a need to use them. I know they are out there, that's all I know.



But even the virtual checks that are an integral part of the layout software are never perfect, but they do catch a lot of issues that would otherwise go undetected until the fecal matter comes in contact with the overhead air movement injectors.





-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Wettermann

Sent: Wednesday, December 20, 2017 4:10 PM

To: [log in to unmask]

Subject: [TN] SW for Proto Builds



Heh All:



One of our customers recently had a small quantity build where he was told by the proto CM that the following was done via SW prior to a build happening…..



Part rotation check (Find this hard to believe as diodes and LEDs are pretty much a source of numerous errors)



Package to footprint fit check (I find this one really hard to believe as there are some variations on this theme)



Part spacing is accurate and within minimum electrical clearance (I find this hard to believe as most people involved in procuring final assemblies do not know what the operating voltages on the board)



Polarity markings that are missing (Same disbelief as above for part

rotation)



The BOM number of placements matches XY data (I can believe this for the total number of placements)



Ours checks for proto assembly include BOM-to-CAD compares, i.e., are all of the parts on the BOM included in the CAD file, no dupes  and vice-versa (that is CAD to BOM.)



Is there a commercial tool that can do the items listed above that help assemblers that I am just not aware of?



Regards and HNY

--

Bob Wettermann

[log in to unmask]

Cell: 847-767-5745


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