Definition:

the steadily increasing miniaturization and the increasingly complex required circuits  – as well as components with high pin numbers – bring the classic multilayer boards more and more closer to the limits of the physical possibilities.  HDI circuit boards offer finer wire structures and smaller through-holes. The micro-vias create space and – in addition – have better electrical properties than classic „thick“ vias or blind holes. By pressing further layers with the Sequential Build Up (SBU) technology, signals can be connected on the inner layers without the need to block space for components with a high pin density. With some experienc and a good layout, these components can even be placed overlapping on the printed circuit board.
(Excerpt from Wikipedia)

In the production of printed circuit boards with a higher packing density, the use of blind holes (defined deep drilling/laser), has firmly established in printed circuit board production. There are two techniques:

— Mechanical blind hole drilling
— Blind hole drilling with laser

Mechanical blind hole drilling has been practiced for several years at ELEKONTA Marek. Drill diameters up to a minimum of 0,1mm are drilled this way. Blind holes have been lasered at ELEKONTA Marek since October 2000.

Important in the use of blind holes is the aspect-ratio. This represents the ratio of hole depth and diameter of the drilled hole. Blind holes can also be produced over several layers (e.g. layer 1 to 2 and layer 1 to 3). In this case the aspect ratio must be considered as well.

Usage:

To dissipate heat on the circuit board, heatsinks are used. These heatsinks are metallic radiators that are firmly connected to the circuit board. Due to the high termal conductivity of metals, the resulting heat is quickly dissipated from the place of origin. By flat application of the heatsink, good dissipation of the resulting heat to the environment can be achieved.

Implementation:

— With copper-heatsinks, a copper surface of 200 μm thickness (typical value) is applied via a prepreg or alternatively via a double-sided adhesive, electrically insulating heat-conducting foil. The copper surface can be electrically-isolated afterwards (upper picture).

Alternative:

— Heatsink by thermal conductivity paste
In the case of heatsinks using thermal conductivity paste, a signle-component heatsink is applied directly by screen printing (picture below).

ELEKONTA Marek also produces circuits that must satisfy a higher current load. There, base copper claddings larger than 70 μm are used. Typical applications are e.g. integrated coils on printed circuit boards. Figure 1 shows a 14-layer multilayer with 140 μm copper lamination on each inner layer and a 70 μm lamination on the outer layers.

Usage:

Areas on the circuit board that should not be tin-plated are covered with removable varnish.

Application:

— in IR soldering (typical parameter: 220-230 °C, 30“ / maximum temperature 250 °C, 10“)*
— In wave soldering (typical parameter: 260 °C, 3“)*
— During chip adhesive curing (typical parameter: 150 – 180 °C, 3“)*
Source: Lackwerke Peters for stripping SD 2952

Characteristics:

— very high thermal steadiness
— very high elasticity and tear resistance
— residue-free removal

ELEKONTA Marek uses solder resist out of the series 2950 from Peters. These are applied via screen printing technique.

Standard layer thicknesses:

Approx. 200 μm

Usage:

Closing of via holes through screen printing.
— Prevents passage of tin solderto the component side
— Prevents flux from getting stuck in the holes
— Seal up for the vacuum adaption

Characteristics:*

— Single component varnish
— Solvent free
— Very high e-corrosion resistance

Rules:

Via holes can be closed before or after the application of the surface finish. For an optimum protection of the via, the print should be applied after application of the final surface. For this purpose it, must be ensured that the vias have been spared in the solder mask on both sides. The side to be printed on must be specified.

Usage:

With label printing, positions of components or information (e.g. manufacturer marks, labels, etc.) are printed on the circuit board. This is done with a state-of-the-art inkjet printer.

The standard color is white, other colors are possible on request!