COMMON DESIGN ERRORS - SPECIFICATIONS

Specification – Specified silkscreen in specification mismatch with gerbers.

Problem description:

Suppose the specification does not mention silkscreen but has silkscreen gerbers in the file package. 

Another problem alternative is that sometimes the specified silkscreen side mismatches with the existing silkscreen Gerber side.  

In most cases, specifications from customers are followed by CAM. But we have experienced several customers needing the silkscreen Gerber but forgot to update the specification correctly.

Solution:

Only have silkscreen files in Gerber if the same silkscreen sides are mentioned in the customer's specification. So make sure that specifications and gerbers are the same regarding silkscreens.

Specification – Impossible or too tight hole tolerances.

Problem description:

impossible +/-0.0mm hole size tolerances are specified, or too tight hole size tolerances are specified. 

Solution:

Only specify hole tolerances if those tolerances are critical and different from quality standard tolerances.

 If hole tolerances are not specified, then automatically, the least quality standard hole tolerances are followed. 

Always avoid specifying +/-0,0mm hole tolerance. Normally plated holes can be specified and need a minimum total 0,15mm tolerance window. This tolerance is a little better than the quality standard. (eg. possible tolerances +0,075/-0,075mm or +0,15/-0mm or +0,10/-0,05mm or +0,05/-0,10mm or +0/-0,15mm). 

For tighter plated pressfit holes total 0,1mm tolerance window is possible. Pressfit hole tolerances are combined with a chemical finish e.g., ENIG. (possible tolerances +0,05/-0,05mm or +0,10/-0mm or +0/-0,10mm). 

For non-plated holes, the minimum tolerance window needed is 0,1mm. (possible tolerances +0,05/-0,05mm or +0,1/-0mm or +0/-0,1mm). 

For plated slots, we recommend at least +0,13/-0,13mm tolerance. 

For non-plated slots,we recommend at least +0,10/-0,10mm tolerance.

Specification – Layer order is missing.

Problem description:

Layer order is missing for multilayers, and layer order may be essential for the correct functionality of the board.

Such missing information will delay the production of the boards as we first need to ask the customer about layer order.  

Solution:

Suppose the Gerber copper files are missing layer numbers. In that case, the designer needs to specify the layer order numbers for the Gerber copper layers (for the layer names) - setting them in the specification or the readme text file.

For example, a six-layer board containing copper Gerber files top, bottom gnd, power, signal and signal. In this case, we wouldn't know the layer order. 

However, if, as an example, the customer specifies the top as(layer 1), gnd (layer 2), signal (layer 3), signal (layer 4), power (layer 5) and bottom (layer 6), then the layer order is specified.  

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