Frequently Asked Questions

Mechanical Features
Why is a space needed between the milling contour and the copper area?
Why can the standard interior milling radius not be smaller than 0.75 / 1.0 mm?

Tolerances
What happens if there are spaces between grounding areas or text areas that are smaller than the manufacturing tolerances e.g. for line width and line spacing?
Are there plotting tolerances in films?
Why do the non-conductive areas in the inner layers of the PCB have to be larger than the minimum annular ring width?
Why should there be text on the copper layer?
Does the line width of the text have to be the same as the line width of the conductive traces?
Is it necessary that drillings have a copper annular ring?
Why is the minimum annular ring width in the inner layers of the PCB larger than in the outer layers?


Solder Resist Mask
Why is there a minimum width for solder resist bridges?
Why should the solder resist mask and the pads have different sizes?


Silk Screen / Marking prin
Why is it not allowed to print the silk screen onto the pads?
Is there a minimum line width for silk screening?


Other Topics
Why is the delivered quantity sometimes larger than the quantity ordered?
SMD stencils with electrical test?

Mechanical Features

Why is a space needed between the milling contour and the copper area?
If the milling contour borders directly on the conductive traces or the grounding areas short-circuits often occur during further processing. Unwanted electrical connections could be the consequence if the case is made of a conductive material. When using wave soldering the solder wave could create tin bridges across the contours. For security reasons we recommend a spacing of 0.5 mm.

Why can the interior milling radius not be smaller than 0.75 / 1.0 mm?
In PCB production we usually use milling cutters between 1.5 and 2.00 mm. The smallest resulting radius is 0.75 mm. When a 90-degree interior angle without a radius is needed, we can mill a 0.75 mm groove into the PCB from both sides. This creates an exact right angle. Naturally, these millings should not touch the copper area. Smaller milling radiuses up to 0.3 mm are of course possible, but this will increase the costs. Bulk milling is not possible when using this option. Milling also takes longer in this case and these costly milling cutters are more likely to break.

Tolerances

What happens if there are spaces between grounding areas or text areas that are smaller than the manufacturing tolerances e.g. for line width and line spacing?
The copper layers will usually be exposed using the positive method. The conductive traces will appear either in black or in reddish brown on the film. Thus, even the smallest gaps in the grounding areas and in text areas will be exposed. After developing the film, these unwanted laminate residues do not stick to the PCB. They can easily detach from the PCB and get stuck elsewhere on the board. When reinforcing the copper layer, copper will be built up on this spot. Thus, this part of the conductive trace will be etched away. A small piece of laminate created by tiny gaps can cause errors and trouble on a different location of the PCB.

Are there plotting tolerances in films?
All materials change size as the temperature changes. The mere absorption of humidity by films during the development process makes them slightly increase in size. This change in size is not 100 % reversible after drying. These materials are stored and processed under strictly regulated ambience conditions in order to keep changes to the film materials as small as possible. For high-end applications, glass plots are used in order to avoid shrinking and expansion due to temperature changes.

Is it necessary that drillings have a copper annular ring?
In the layout, drillings show the final diameter needed by the designer. Through connections and above all the copper reinforcement always make it necessary to drill larger holes than in the layout. Without the overlapping annular ring the rivets in through connections are less stable and therefore more likely to break out. The annular ring width in the outer layers is usually 0.3 mm larger than the drilling diameter. Due to the copper reinforcement, we calculate approximately +0.15 mm. The resulting annular ring width for processing is 0.075 mm.

Wie kommt es, dass die Restringbreite in den Innenlagen größer ist als in den Außenlagen?
Durch das Verpressen kann es in den Innenlagen zu leichten Versätzen kommen. Daher ist an dieser Stelle ein größerer Restring erforderlich. Der Restring ist um 0,5mm (Außenlage 0,3mm) größer als der Endbohrdurchmesser. Natürlich sind auch kleinere Restringe zu verarbeiten. Doch kann dies zur Folge haben, daß in der Innenlage eine Sichel entsteht, weil die Bohrung den Ring leicht aufbohrt. Elektrotechnisch ist dies zwar unerheblich, doch für ein optimales Erscheinungsbild wirkt es störend.

Why is the minimum annular ring width in the inner layers of the PCB larger than in the outer layers?
Pressing can cause slight shifts in the inner layers. Therefore, a larger annular ring width is necessary in the inner layers. The annular ring width is 0.5 mm larger than the final drilling diameter (0.3 mm in the outer layers). Naturally, we can also process smaller annular rings. However, this may result in uneven ring shapes in the inner layer because the drilling slightly opens the ring. This is of no importance for electrical functions but it disrupts the appearance of the PCB.

Why should there be text on the copper layer?
Text in the copper layer is necessary to make sure the layer is not side-inverted. When processing the data the text makes it easier to check for inversions. We strongly advise you to place some text in the copper layer.

Does the line width of the text have to be the same as the line width of the conductive traces?
The same technology is used for text and for conductive traces. Type faces with small line widths could easily be etched away during processing. If the letter spacing is too small or if there are spaces within one letter they can easily fill with copper during copper reinforcement.

Solder Resist Mask

Why is a minimum width necessary for solder resist bridges?
Solder resist connections between tightly adjoining pads are called solder resist bridges. If those solder resist bridges are too small (<0.1 mm) they detach because they have no support on the board. They can end up on the pads and impair proper soldering, thus damaging the results of your work. This applies especially to integrated circuits with a small pitch. If the IC components used have a small pitch and the spacing between pads is smaller than 0.2 mm we recommend using a mask. The solder resist mask should be applied to the entire pads without solder resist bridges. It should be 0.1 mm larger than the pads.

Why should the solder resist mask and the pads have different sizes?
Due to manufacturing tolerances, a solder resist mask that is applied 1:1 will hardly ever fit accurately. When reinforcing the copper layer, copper will be built up on this spot and create soldering problems. To avoid these problems, solder resist pads should always be 0.1- 0.2 mm larger than the pads (0.05-0.1 mm ring width).

Component Marking / Silk Screen

Why is it not allowed to print the silk screen onto the pads?
If the pads are free of silk screen print this ensures trouble-free soldering. Every design software has comfortable tools that allow you to cut out text from the silk screen. This may result in illegible text. Therefore we recommend to never place the component designation on a pad. Use the solder resist mask as a reference.

Is there a minimum line width for silk screening?
The component marking is produced using silk screening. The screen is made of a finely-woven fabric with approximately 100-120 threads per inch (4-5 threads per mm). A mask covers the non-printable areas. The ink is applied through the openings in the mesh. Considering the number of threads and the spaces between them, the smallest theoretically possible line width is approximately 0.1mm. In practice, line widths between 0.18 and 0.2 mm are necessary to make the print continuously visible. Technically speaking, smaller screens are inefficient. They are too sensitive and due to the smaller mesh the ink would be difficult to place on the board.

Other Topics

Why is the delivered quantity sometimes larger than the quantity ordered?
In PCB manufacturing as in the printing industry, batches are larger than the order quantity to ensure that the requested quantity is available at the end of the process. This compensates for unforeseen rejects. We always try to avoid excess quantities and smaller quantities or to keep them as small as possible. We only guarantee to deliver the exact quantity for our “Hot Shot“ PCB service. When you order PCB prototypes, we will even deliver you the excess quantities resulting from the manufacturing process for free. The PCB Printed circuit pool system however, makes it necessary to manufacture the PCBs on one panel. This requires larger batches. We are happy to advise you in detail on these matters. When ordering PCBs you should, however, not plan any excess quantities in the first place. Deliveries of excess quantities are rare with Basista.

SMD stencils with electrical test?
Naturally, we do not perform an electrical test on SMD laser stencils (Hot Stencil Service). When producing an SMD stencil, a “beam break” may occur. This is a short interruption of the laser beam cutting the SMD holes. Later, during component placement, this can lead to substantial problems: for example capacitors may not be soldered completely but only on one side. Everyone involved in component placement will know the “tombstone effect” (lifting of the SMD component on one side like a tombstone). We recognise this error by performing a scan check on each SMD stencil. Each hole is checked for its exact measurements and its position on the stencil. This helps to avoid later manufacturing problems and additional costs..

Do you have problems with soldering lead-free PCBs?
There is no end to the questions about whether lead-free PCBs are just as easy to solder as leaded PCB surfaces. In our experience, there is no disadvantage to using lead-free PCBs if the right tools are used.

Here are some simple rules to make hand soldering easy:

• The soldering iron should quickly reheat during use.
  A big soldering tip is too slow to quickly heat up and transport the heat to the soldered joint.

• Please take your time to let the heat spread on the soldered joint.

• Please choose an adequate soldering temperature. Chemical tin has a higher melting point than a lead tin alloy.
  
  

• Wherever possible, use flux. This helps you to spread the heat and to reactivate the solder.

You can easily order suitable soldering aids here.

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