Here we have collected the most frequently asked questions and topics that are being asked literally every day, over and over.
1) Mask openings need to be reduced? Why? How much?
This is something we can fix for You if you give us written permission to do so.
Too big mask openings constitute a problem in the later soldering process – without properly reduced mask openings there is a danger of “solder bridge” between metallized areas / pads / wires etc.
This may result in an unwanted connection and shorts. There is no specific numerical value we can give to the question “How much exactly do you decrease mask openings”? It is all done depending on each case separately, sometimes it can controversially mean that we need to actually enlarge openings in some places. We do it as little as possible and as much as necessary, all related to our own in-house know-how and 20 years of experience.
Mask openings need to be corrected:
Correct mask openings:
2) Unbalanced topography? What does it mean and what is the worst case scenario? How do I “balance” it?
Equalizing topography means balanced (equalized”) copper layer – meaning there is no big copper area differences – like huge earth plane in one corner of the board and just narrow tracks in the opposite corner. In such case narrow tracks will be over plated during galvanization process – copper thickness will be twice as thick when compared to the earth plane area. In the worst case scenario that will lead to merged metallized areas/pads/wires etc. Different thickness of plating across the board in itself is already an obvious problem regarding impedance control.
1) Add metallized planes where possible (opposite direction of existing ones)
2) If boards are panelized, give us permission to metallize the frames
See the illustrations below for visual description of the issue:
All green areas are copper. Note the total difference in the coverage of the left and right
sides of the board.
3) Milling cuts the copper? What can happen?
Depending on how seriously and where the cutting path interferes with the metallised areas, this issue can be either cosmetic or a major problem. Usually the open cut copper edges are lifted slightly up by the router as it cuts through the material (also known as “burrs” – very slight protrusions around the router path) – this can definitely create problems if the board has to go into automatic soldering machine, where it can interfere with the proper and tight stencil application on the board. “We will always inform You of this type of problem and always recommend You to fix this. You need to take full responsibility for Your design when giving us a “don’t stop, produce” written order.
4) “There is a danger of mask pocket”? What does it even mean and why is it dangerous?
Mask pocket = mask over via on one side only. Other side of the via is open, creating a closed “pocket”. Why is this sloppy design: making PCB-s involves enormous amounts of chemical solutions the board has to go through. It is almost impossible to wash out these solutions from mask pocket with 100% certainty. That means the chemical leftovers inside the pocket will create a plethora of unexpected problems once they start leak out later, during other processes – in other words, contamination. This will most likely influence the affected areas finishing. Please design smart – do not leave mask pockets anywhere. See IPC standard image below:
5) “There is a resist pocket on your board”? What does it even mean and why is it dangerous?
The general method of manufacturing printed circuit boards involves a method where copper foil is coated with photo-resist, intended to be partially removed later.
In the developing-process, the light-sensitive resist is exposed to light in order to create a design pattern. The resist outside of the pattern then is removed and the unwanted copper etched out.
If there are sharp angles or too narrow gaps left in the design, there is a risk that unneeded resist-material gets stuck and consequently comes loose in later production stages. This can result in unwanted shorts. To avoid that, we ask our customers to correct their design, avoiding sharp angles and taking care that no design elements are poorly joined.
Sample of poorly joined details , figure A. There is no need to leave strips like ones shown in red frame. Same place corrected is shown on figure B.
6) Why do the single boards or panels have to have rounded corners?
To maintain maximum safe transportation and storing all boards are packed airtight in the anti-static bubble wrap. The corners are rounded to avoid sharp points pricking the bubble wrap when parcel is handled.
Should you need the boards with sharp corners, please order them in panel (V-scored and framed) or add 2mm frame at least 5mm wide intended to be separated with v-cut to two opposite sides of your board.
7) Drill depth limits, Aspect Ratio – what does it mean?
Aspect Ratio is a dependence between drilling depth and drill diameter. For Brandner PCB aspect ratio for through holes must be 1 to 16. It means that it is possible to drill through holes with depth no more than 16 times the drill diameter. For example – because of aspect ratio it is possible to drill 0.1 mm through holes to the board with total thickness up to 1.2 mm, no thicker.
For blind vias it is vital to maintain aspect ratio 1:1. It means that if blind drills are needed, the drilling depth has to be less than or equal to drill diameter. Please do not forget it when planning a stackup for a board with blind vias.