Blind vias are plated-through holes that connect the external layer of a printed circuit board with internal ones without going through the entire PCB.
\nThe hole is drilled on the Z-axis, and its diameter must ensure optimal metal coating on the walls.
\n5 parameters help you choose a suitable blind via diameter and thus ensure quality and reliability over time.<\/p>\n
To avoid criticalities and ensure durability, the PCB design must consider: Blind via holes can be laser or mechanically drilled:<\/p>\n – A MECHANICALLY-DRILLED HOLE<\/em> can be made using a tool with a minimum diameter of 0.15 mm (with a negative tolerance of 50 \u00b5m). This way, after the metallisation process, you can obtain a hole with a 0.05 mm diameter (or slightly larger).<\/p>\n – A LASER-DRILLED HOLE<\/em> has a diameter of 0.1 mm (without negative tolerance) to obtain a hole with a 0.05 mm diameter (or slightly smaller).<\/p>\n Please note: a plated blind hole includes the CU plated wall with a minimum thickness of 12 \u00b5m, as indicated in the IPC standard.<\/p>\n The blind via pad must have a diameter of at least 300 \u00b5m (11.8mls) larger than the blind via diameter (after CU plating – considering layers with a copper thickness of 35 \u00b5m) to comply with IPC standards and ensure an optimal PCB. The thickness of the insulators and conductive layers depend on electrical design requirements. This also applies to the layers involved in blind vias. (It is related to the Aspect Ratio).<\/p>\n Aspect ratio refers to the ratio between the hole\u2019s depth and hole\u2019s diameter<\/strong>. Aspect Ratio is important due to the chemical, physical and fluid-dynamic limits of the electrolytic plating process applied to the holes. During the galvanic coating process, different liquids must flow inside a cylinder created by the blind drilling. i.e., the diameter of the annular rings must depend on the thickness of the dielectric and copper layers (hole depth maybe only slightly wider than the hole diameter).<\/em><\/p>\n It refers to the dielectric thickness between the second layer connected to the blind via and its adjacent inner layer (underneath), which is not connected. According to the tolerances required by the Z-axis-controlled drilling process and the shape of the drilling tool, this thickness must ensure correct electrical insulation at the end of the process.<\/p>\n Suppose you have a PCB with 35 \u00b5m-thick copper layers, where 100 \u00b5m of dielectric material insulate the top and the first inner layer, and 150 \u00b5m (E<\/strong>) of material insulate the second inner layer. In this case, you can engineer a blind via with a 150 \u00b5m diameter (C<\/strong>) (no laser) centred on copper pad having a diameter of 450 \u00b5m (A<\/strong>). This hole is made with a 250 \u00b5m-diameter tool (B<\/strong>), which crosses a material thickness (FR4 + copper layer) equal to 170 \u00b5m (D<\/strong>). This way, AR reaches 1.13:1 (D\/C), which is lower than 1.4:1. This ensures excellent performance.<\/p>\n Minimum values:<\/strong><\/p>\n Guidelines for using blind vias. BLIND VIAS AND CONSTRUCTION PARAMETERS Blind vias are plated-through holes that connect the external layer of a printed circuit board with internal ones without going through the entire PCB. The hole is drilled on the Z-axis, and its diameter must ensure optimal metal coating on the walls. 5 parameters […]<\/p>\n","protected":false},"author":1,"featured_media":2262,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[3],"tags":[],"class_list":["post-2293","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized"],"acf":[],"yoast_head":"\n
\n\/5\/ PARAMETERS TO CONSIDER WHEN USING BLIND VIAS<\/strong><\/p>\n
\n1. Drill size (hole diameter)
\n2. The size of the copper pad connected to the blind via
\n3. The thickness of dielectric material between the layers connected through the blind via plus the copper layer
\n4. The Aspect Ratio of the hole
\n5. The insulation thickness of the underneath layer not connected to the hole (mechanically-drilled holes only)<\/p>\n
\n1 – HOLE DIAMETER
\n<\/strong><\/p>\n
\n2- SIZE OF COPPER PAD CONNECTED TO THE BLIND VIA
\n<\/strong><\/p>\n
\nThis aspect is essential for centring the hole on blind via pad while maintaining the required hole size.
\nFor laser-drilled holes, this value can be reduced to 250 \u00b5m (10 mls).<\/p>\n
\n3- INSULATION THICKNESS BETWEEN THE 2 LAYERS CONNECTED THROUGH THE BLIND VIA
\n<\/strong><\/p>\n
\n4- ASPECT RATIO (AR) \u2013 (after CU plating)
\n<\/strong><\/p>\n
\nNote:<\/em>
\n– The hole\u2019s depth is given by the dielectric thickness between 2 connected layers plus the copper layer thickness;\u00a0<\/em>
\n– The hole\u2019s diameter is after CU plating.<\/em><\/p>\n
\nThis process is carried out to obtain a durable metal coating of the hole wall and a reliable electrical connection.
\nThis ratio must be a maximum of 1.4:1.<\/p>\n
\n5- INSULATION THICKNESS BENEATH THE HOLE (mechanically-drilled holes only)
\n<\/strong><\/p>\n
\nEXAMPLEOF A RELIABLE BLIND VIA<\/strong><\/p>\n![\"Fori](\"https:\/\/albapcb.com\/wp-content\/uploads\/2021\/03\/Tabella-fori-ciechi-ENG-disegno-1-scaled.jpg\")
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