It is a means to protect the through-holes (Via Hole) for several reasons:
- To prevent the tin flow from one side to the other in the soldering process. May cause ‘shorts’.
- To avoid chemical residues being trapped inside via-holes in subsequent processes, than can contaminate plating causing ‘open’.
- For heat dissipation.
- To enable assembly or solder directly on the through hole. VIP Technology (Via in Pad).
- To get a completely flat surface on the circuit, and improve vacuum in the ICT test.
- To provide additional reliability to the through hole or via.
The through-holes can be protected with 2 materials:
- With non-conductive inks.
- With conductive inks or filled with copper.
The way to do this is known as 5 types:
- « Plugged » – partially covered with non-conductive ink.
- « Plugged & covered » – partially covered with non-conductive ink and then covered with a second layer of ink.
- « Filled », filled 100% with non-conductive or conductive ink.
- « Filled & Covered » – completely filled and subsequently covered with a second layer of ink.
- « Filled & Covered Plated » – completely filled and subsequently covered with a layer of copper plating.
Plugged vias are typically used to prevent the transfer of tin between both sides on soldering process. Are also used to achieve vacuum during the ICT Test. Plugged is a partial penetration of ink into via hole and can be applied before or after the end application process of the Solder Mask.
The filled vias usually are made with conductive ink or complete copper plating (blinding and filling the hole). Are used for VIP (Via in Pad) as heat sinks, or to ensure the reliability of the via (With an encapsulated 100%). (See Standard IPC-4761).
Before designing the PCB, is recommended to contact directly (without intermediaries) with assembler (OEM) and manufacturer of printed circuit boards. They are really the true specialists in all matters relating to the PCB in both the manufacturing and assembly of printed circuit boards. They can advise on all matters relating to:
Materials to use, recommended multilayer construction (Build Up), panelized circuit, protection type of via, finishing recommended…
It will be the real way that the prototype resembles the intended end and reduce costs. (See Standard IPC-2221a).
The preferred format is Gerber RS274X, with the Apertures Table included. Files should include all layers, Solder Mask (“Top” and “Bottom”) and the Components Legend. Drill file format must be in “Excellon”. They are also accepted other formats such as DPF, DXF, etc …, but it takes longer for Gerber conversion with the risk that on conversion errors might occur.
It is suggested to send a text file with main items necessary for the manufacture of printed circuit as thickness and type of material, Solder Mask colours and any other significant data.
It is recommended to store the PCBs in the original packaging until assembly in a dry and clean place with a level not exceeding 25 °C of temperature and 60% of humidity.
Once the package is opened, if all the pieces have not been used, close it again.
Handle the PCB’s carefully, paying special attention to not touch with the fingers the solder points (wear gloves), it may produces oxidations affecting solderability.
If circuits are assembled several weeks after the reception, it is recommended to softly drying in the oven (can be stacked) about 4 hours at 120º C, to eliminate humidity content age, which could affect solderability.
The maximum storage periods depending on finishing are:
Immersion Tin – 6 months
Immersion silver – 6 months
HAL Sn/Pb – 12 months
HAL-LF- 12 months
ENiG – 12 months
Hard Gold – 12 months
OSP – 6 months
The polymers (plastics insulation) used in electrical and electronic contact such as inks mask and base materials for manufacturing PCBs, printed circuit itself, wires, plugs, transformers, etc. are regulated by various international and national standards (UL, IEC, DKE,CENELEC) to ensure, mainly among others, the electrical safety of installers and users, and fire safety.
U.L. is an acronym for Underwriters Laboratories Inc., a US organization that certifies, after investigation and implementation of relevant tests, compliance for electrical and electronic equipment, and all its components, electrical safety requirements (CTI and DSR) and safety fire (Flame Class – flammability classification), among other requirements (*), according to national standards of the United States and Canada.
(*) Its ability to keep their properties to the operating temperature limits of maximum soldering and design parameters such as the minimum width of the tracks, distance from the tracks to the edges, thickness of the track, finishing, number of coating layers and the high area conductive.
The majority of circuits manufactured in CIPSA are UL recognized components for both standard US and Canada.
The identification means “UL Recognized Component”. Placed on the PCB’s indicates that such products, as well as base materials and inks mask with which they were manufactured, have been evaluated, classified and recognized by UL as a component that meets safety standards US.
For the recognition of the circuits as components that meet the safety standards in CIPSA for marking is our logo plus letter according to the type of circuit.
ATTENTION !!!
For marking the PCB’s as a recognized component must be previously requested by the client, indicating the country (US or Canada) where it is required. Considering also that for the European market usually requires UL recognition for certain electrical and / or electronic devices. In these cases is used by default United States identification.
C.T.I. is the Comparative Tracking Index.
The Tracking is defined as: the irreversible degradation of the insulating material surface by of tracks forming due to discharges that are initiated and develop superficially. These grooves are conductive even in dry conditions. The tracking may occur on surfaces in contact with air and also at the contact surfaces (interfaces) between the different materials.
For electronics market electrical industry reference data are especially important.
CTI is one of many methods used to measure the properties and behavior of the insulating materials with electrical and / or electronic use in the presence of electric current. Applied to the PCB’s allows the Final Equipment Manufacturer to select the right type of circuit according to the requirements of his product.
The value of CTI indicate the degree of resistance of the base materials for the production of printed circuit boards, to the formation of conductive paths (short circuits) when its surface is exposed to humid conditions, the action of water containing ionic impurities, simultaneously with electricity demand.
The test is performed according to standard UL 746E.
With this value of the base material, the PCB is classified according to the ranges specified in UL 746A standard and indicated in the following table:
CTI 0 > 600 Volts
CTI 1 400 – 600 Volts
CTI 2 250 – 400 Volts
CTI 3 175 – 250 Volts
CTI 4 100 – 175 Volts
CTI 5 < 100 Volts
ATTENTION !!! The most common values CTI in materials for circuit fabrication are those corresponding to PLC 3 and 4. Usually, when a final device have certain electrical safety requirements, the client required for the printed circuit the value of CTI = 3, that is, the base material used for manufacturing meets best electrical characteristics, greater resistance to the formation of short circuits by passing electric current during its operation with CTI> 175 V.
D.S.R. is the Direct Support of Current-Carring Parts
When it is indicated that a printed circuit board meets DSR is understood that the basic material that has been manufactured meet the electrical requirements of ANSI / UL 796 standard.
Applied to the PCB allows the Final Equipment Manufacturer can select the right type of circuit according to the requirements of his product.
FR4 is the most commonly used material for the manufacture of printed circuit boards, as defined by NEMA as: Epoxy resin laminate and glass fabric with very high mechanical characteristics at moderate temperatures, with good stability of electrical properties at high humidity and flammability characteristics defined. The letters “FR” in the designation indicates material containing Flame Retardants, it is flame resistant materials (self-extinguishing).
In the characterization the thermal behaviour of epoxy polymers various parameters are used:
– Flammability class. The regulation for the evaluation of flammability applied to electrical and electronic equipment is ANSI / UL 94. According to this standard FR4 materials used by CIPSA have Flammability Classification Rating 94V-0.
Flammability classification UL established for printed circuit boards, inks and base materials used in its manufacture, is made based on the results of the tests according to ANSI / UL 94 (« Tests for Flammability of Plastic Materials for Parts in Devices and Appliances »).
In CIPSA it is established that all base materials and inks mask must have flammability UL 94 V-0.
As a result of the above classification of raw materials used and the manufacturing process employee who has not modified its conditions of flammability, CIPSA circuits, tested and recognized by UL, also has flammability UL 94 V-0 from a total minimum final thickness of 0.5 mm forward.
– (Tg) Glass Transition Temperature. At temperatures above Tg, the epoxy polymer is transformed to deformable and brittle with the behaviour such as high viscosity liquids. This situation is reversible.
The FR4 materials are classified according to their Tg as:
Standard Tg 120 – 140º C
Medium Tg 140 – 165º C
High Tg >165º C
– (Td) Decomposition Temperature. The temperature at which thermal destruction of epoxy polymer is caused, causing weight loss of the material and its physical and chemical degradation irreversibly.
– (MOT) Max. Operating Temperature. In addition to mechanical changes, the temperature can also affect the electrical performance of a PCB in the case of high temperature because of high power operation.
The maximum operating temperature of a PCB is determined by the characteristics of the materials used in manufacturing, basically the values RTI.
MOT must also stay below Tg, except for processing steps of short duration, such as soldering processes. Above Tg the material becomes mechanically and electrically unstable because suffered drastic change in the CTE (Coefficient of Thermal Expansion).
– (RTI) Relative temperature index. Maximum temperature at which the critical material properties are engaged unacceptably due to their thermal degradation.
– RTI electrical, maximum temperature of critical engagement with insulation and electrical properties.
– RTI mechanical, maximum temperature of critical engagement with mechanical properties and structural integrity.