FAQ`s
What is a material's CTI?
It is the Comparative Tracking Index, used to measure the electrical breakdown properties of an insulating material. IEC-950 standards classify materials according to the following table:
| GROUP | Minimum width (Tw) |
|---|---|
| I | 600<=CTI |
| II | 400<=CTI<600 |
| IIIa | 175<=CTI<400 |
| IIIb | 100<=CTI<175 |
The FR4 standards applied at 2CI belong to the group IIIa, specifically 175V<CTI<250V.
What is a material's Tg?
From the English term glass transition, these initials indicate the temperature at which the material that makes up the base of the printed circuit board starts to become more elastic and bendable.
The FR4 standards used at 2CI establish Tg= 140ºC. For high Tg needs, we offer a base with Tg= 175ºC, refered to as high Tg.
What is UL marking?
It is the guarantee that the raw materials meet the specifications of UL 94 standards. For FR4, the level established is UL94 VO. This means that when a vertical sample of a material is subjected to a flammability test it stops burning within 10 seconds, with no dripping particles. This marking is the only way to prove that the product has been certified by UL (Underwriters Laboratories). So, this marking must be requested before the manufacturing process, on the order or in the PCB technical specifications section. Once the product has been manufactured, it cannot be marked and therefore it can’t be certified with any document.
What is RoHS marking?
The RoHS logo indicates that the product complies with Directive 2002/95/CE and 2011/65/CE on the Restriction of Hazardous Substances in electrical and electronic equipment containing lead. Only circuit boards that do not contain these substances can be marked with this logo. All the circuit boards manufactured at 2CI meet the standards established in the RoHS Directive.
What documents do I need to send to manufacture a printed circuit board?
To manufacture a printed circuit board, we need an image for each layer in the board and a file with the position and diameter of the drills.
So, we need one file for each, internal and external layer, solder mask, legend marking, peelable mask, carbon ink, etc. and the board outline. We will cut the circuit board down the centre of the board outline, regardless of how thick they are. Other specifications must be indicated.
The preferred format for this information is GERBER 274X for images and EXCELLON for drilling information. The GERBER file resolution should be at least 2.5 inch and the drilling resolution and units should be the same. You shouldn’t make mirror images of any layers and try to make sure all of the layers are aligned.
It is also important to send mechanical plans in PDF or DXF and a text document, word or similar, with the specifications of the printed circuit board to be manufactured: thickness of the base material, colour of the solder mask, final copper microns and other considerations.
What file formats can be used for manufacturing?
Only GERBER for images, preferably 274-X, and EXCELLON format without ASCII character extension (ASCII None) for numerical control information, whether for drilling or milling.
In some cases, we will accept other formats, such as DXF, ASCII files from Tango PCB or DPF, but always with one image on each side so the customer can confirm that is correct before starting production.
How should I indicate slots or windows in the design?
Design slots can be included on the same layer as the circuit board contour line or on a separate one.
There are two ways to draw slots: one is with tool compensation, which shows the exact dimensions of the edge of the window with a thin trace line so that the material will be removed from the inside of the centre axis of the line drawn. The other is without tool compensation, drawing the axis of the slot with a line that is as thick as the slot, so the axis of the line drawn will be used to guide the tool of the same diameter as the thickness of the line drawn.
How long can I store my circuit boards?
Depending on the finish on the circuit board: more than 2 years for a flash-gold finish (electrolytic nickel gold).
What is the maximum measurements for manufacturing 1, 2 or multilayer FR4? And for aluminium?
For multilayer circuit boards, the maximum size is 330 x 452 mm.
For 1 and 2-layers FR4 or aluminium circuit boards the maximum size is 465 x 590 mm. For sizes just beyond these measurements, ask us about feasibility.
Is it possible to manufacture a circuit board from a physical sample?
Yes, by digitising it (drawing the circuit board in digital format). To do so, we need the board without any components.
Nevertheless, this is only possible with relatively simple circuit boards. For more complex circuit boards, we recommend sending this to a specialised company.
What is the minimum Cu thickness for 0.25 and 0.35 mm fibre?
Our baseline Cu thickness for 0.25 and 0.35 mm fibres is 35 μ/35 μ, so our minimum thickness is 35 μ+20 μ for our production process.
What is the minimum plated mill?
The minimum plated mill is 0.65 mm diameter. The length must be twice the diameter.
What is the minimum trace thickness for the baseline Cu?
For baseline Cu of 17 µ we can use 0.125 mm (125 µ)
For baseline Cu of 35 µ we can use 0,20 0mm (200 µ)
For baseline Cu of 70 µ we can use 0,250 mm (250 µ)
What is the minimum separation between traces for the baseline Cu?
For baseline Cu of 17 µ we can use 0,150mm (150 µ)
For baseline Cu of 35 µ we can use 0,200mm (200 µ)
For baseline Cu of 70 µ we can use 0,250mm (250 µ)
What is the minimum for drilling and milling?
The minimum for drilling is 0.25 mm and for milling it is 0.8 mm.
