DRC & DFM
DRC and DFM are test routines that analyse a data set according to predefined parameters. We use both to check manufacturability at the quotation stage.
Design Rule Check (DRC) is an integral part of the layout process and has been used for decades. With the aid of stored basic parameters, the search for defects begins for structures that fall short of spacings and widths. It also checks the integrity of the signal network across all layers of the board.
However, a successfully completed DRC test of the layout only makes a limited statement about the manufacturability.
The Design for Manufacturing (DFM) test can be seen as an extended failure analysis, but related to the DRC.
Both are subject to predefined parameters. Unfortunately, these often do not reflect the production process used.
This contributes significantly to the fact that 80% of the data goes into production with layout changes. In practice, this means a lot of administrative work for everyone involved. The cost of a PCB increases enormously if the manufacturing process has to be interrupted or corrected. The same applies to the product cost of a PCB. Conversely, production-ready DFM & DRC principles that are already integrated into the layout design save a large number of revisions and are therefore worth their weight in real money. At the same time, they reduce time and complications - which ultimately has a positive effect on quality.
DFM is the definition of basic rules and controls that ensure a smooth manufacturing process. Besides the material and the manufacturing process, this set of rules related to the layout, is relatively simple and is widely applicable across technologies.
Copper areas & feature sizes are the start of what manufacturers call a good manufacturable layout. Copper should be present in as large an area as possible - important for homogeneous resin distribution, avoiding short circuits and ensuring a uniform dielectric constant.
Structures - Trace widths and insulations deserve a lot of attention - just because the finest structures are possible doesn't mean they are necessary. Trace widths and insulations are very closely correlated - a good layout ideally takes this into account with the widest possible values. It is a compromise between what is technically necessary, the technologies and the material constructions.
Layout - Acid Traps
Narrow recesses, sharp corners and 90° angles concentrate and fix the etching medium, which can lead to over-etching of these areas. Structures that are as wide open as possible or rounded compensating loops improve the situation.
Mechanical Contour Machining
Contour Machining - Milling
Milling of a PCB supplied as a single piece or in a panel array with non-perforated bars requires a minimum clearance of 0.25mm.
Milling - with perforated bars
Perforated bar joints ensure that no material protrudes over the edge when the part is separated. To achieve this, the holes of the perforation are placed 0.1 and 0.2 mm inside the board. This increases the required copper-free clearance to 0.5 mm.
Contour machining - scoring
A score runs at a 30 degree angle on both sides along the edge of the board. The minimum distance of the copper from the scored edge is determined by the manufacturing tolerance, the final thickness of the board and the depth of the scoring. The latter two factors determine the thickness of the joining material - the remaining web.
Final material thickness up to 0.8 mm = requires 0.25 mm minimum distance from copper edge to PCB edge.
Final material thickness up to 1.6 mm = requires 0.40 mm minimum distance from copper edge to PCB edge.
Final Material thickness up to 2.0 mm = requires 0.50 mm minimum distance from copper edge to PCB edge.