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Following some articles related to HDI PCBs we would like to describe the three related more common build-up structures.
HDI PCB types
The design designation system of this standard recognizes industry approved design types used in the manufacture of HDI printed boards. The designations determine the HDI design type by defining the number and location of HDI layers that may or may not be combined with a substrate.
Type I, Standard build-up for HDI
This construction describes an HDI in which there are both blind vias and through vias used for interconnection. Type I constructions describe the fabrication of a single blind via layer on either one or both sides of an PCB substrate core.
The PCB substrate is typically manufactured using conventional PCB techniques and laser via hole technology. The substrate can have as few as one circuit layer or may be as complex as any number of inner layers.
Type II, Sequential build-up 1+N+1
Tipe II is characterized by buried vias in the core and may have through vias through the outer layers. Type II constructions describe an HDI board in which there are plated microvias, plated buried vias and may have PTHs used for surface-to-surface interconnection.
Microvias on layer 1 and layer n grant the connection to conductors on layer 2 and layer n-1, making the connection with the core. Type II constructions can also have PTH to connect layer 1 directly to layer n.
Struttura Tipo III, build-up sequenziale X+N+X
Type III constructions describe an HDI in which there are plated microvias, paste/resin filled holes and through vias used for interconnection. Type III constructions are distinguished by having at least two microvia layers on at least one side of a substrate core. The substrate core is usually manufactured using conventional PCB techniques, may be rigid or flexible, and have as few as one or as many as any number of layers with buried vias.
Where space is minimal and if expressly requested, stacked vias - stacked blind holes - must be used - while where conditions allow it, staggered vias - non-overlapping blind holes on several levels - can be used. Staggered vias are less critical, so preferable, for manufacturing than stacked vias.
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mrt 31 2021
Datum 31 maart 2021 11:51
The capped vias technology with hole filling with resin aims to increase the density of the interconnections in printed circuit boards by using the space occupied by through holes as SMD assembly points. This technique consists in filling the holes after plating them, with copper thicknesses on the walls, normally >25µm, and, in any case, defined with the customer.
The resins adopted for "filled and capped vias” have specific insulation properties and dimensional variation with temperatures, they are treated with heat for the relative polymerization and consequent hardening, and, subsequently, are first planarized and then covered with a layer of copper with a thickness of at least 15µm.
This technique can be applied for the realization of different types of printed circuits and with multiple application variants which for this reason are in strong expansion:
- pads used for µBGA, "ball on via technology" and SMD assembly: "Via in Pad Assembly Technology"
- pads used as test points, "Via in Pad Test Technology”
- heat dissipation pads under the cases of the components for "heat management”
- SBU - sequential build up" construction with laser stacked holes on buried holes treated as capped vias
The fundamental operations for filling the holes with resin are carried out in two distinct phases: in the first, the holes are filled with variable pressure and vacuum to allow perfect filling of the holes without the risk of gaps in the resin, while, in the second phase, a surface cleaning of the panel is performed to eliminate the excess resin, facilitating its subsequent planarization.
Whatever the final technology chosen, after complete polymerization, the resin is removed by a mechanical brushing action, called planarization, which can be performed with specific machines that work with cup brushes or with horizontal brushing machines.
The target is to remove the excess resin and create a uniform surface: this operation is a prerequisite for the subsequent over-plating of the filled vias with copper to allow ideal soldering of electronic components. (inserisci disegno).
The knowledge of "capped vias" technology is fundamental today to create compliant pcbs to market and regulations standards required, especially relating to the growing HDI technology demand.
feb 25 2021
Datum 25 februari 2021 16:08
This trend is imposed by the market demand for increasingly portable devices, therefore of low weight, and capable of integrating many functions: the real challenge is to reduce the size of the devices, miniaturizing them, and, at the same time, to increase their performance.
The target can be reached basically by working on the structure of the printed circuit board by increasing the density of the components on the surface and the number of connections between the layers that make it up: this need has therefore led to the birth and diffusion of " HDI - High Density Interconnection" structures.
All circuits with pitches’ density per surface with values greater than 20 pitches/cm² greater than traditional printed circuit boards (PCBs) are defined as high interconnection density PCBs (HDI). This therefore results in smaller size for design parameters such as tracks less than 100 ?m/4mils wide, laser holes with a diameter less than 150 ?m/6mils and pitches with a diameter less than 400 ?m/16mils.
feb 9 2021
Datum 9 februari 2021 7:52
In particular, we have highlighted that the moisture absorbed by the base material can generate delamination during the assembly of PCBs.
With this second article, relating to the risks generated on PCBs by the presence of humidity, we deepen the subject and deal, in particular, with the impact of humidity on the Tg of the base materials and the consequences on the quality of PCBs and PCBAs.
The Tg of a polymeric material (laminates and pre-impregnates are partially made of resin) represents the temperature value at which the glass transition begins which we could define as the temperature at which the resin changes its mechanical characteristics starting to soften: for this reason it is important to choose the base material in relation to the expected conditions of use of each PCB.
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jan 25 2021
Datum 25 januari 2021 7:39
nov 28 2020
Datum 28 november 2020 23:00