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next page 01 | 02 | 03 | 04 | 05 | 06 | 07 | 08 | 09 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 17 – Filling / Sealing of viasThe filling/sealing of plated through drill holes (vias) should prevent a run-off of solder during the soldering process or allow inspection in a vacuum adapter. The vias can be filled/sealed as follows:• Covering with solder resist • Via fillers • Galvanic copper plating • Plugging 17.1 – Covering with solder resistThe vias are covered during the production process using solder resist. To do this, they are not exposed to the solder resist. The disadvantage of this procedure: The vias are not sealed 100 % reliably as the solder resist hardens and can tear. In addition, they are not sealed vacuum tight. This procedure is frequently used in association with BGAs. However, chemical and moisture residues can lead to corrosion, surface wetting and solder problems. For this reason, this procedure cannot be recommended without reservation.The better solution is to print the solder resist up to or on the annular ring. Solder resist openings should be +0,1 mm to the annular ring or by printing on the annular ring +0.15 mm to the drill.
17.2 – Via fillers
17.3 – Galvanic copper platingThis sealing method is only possible in case of small diameters. To do this, the PCB is covered except for the relevant vias and these are galvanically copper plated. However, this procedure is very time consuming.17.4 – Plugging PCBsThere are two plugging variants, depending on whether the pad surface has to be capable of being soldered or not. As an alternative to via fillers, normal vias can be plugged (HP = Hole Plugging). If, in order to save space, the via is placed directly in the pad, the surface must be metallically conductive in order to be able to solder on to it later on (HPL = hole-plugged land). To do this, the drill holes to be sealed must first identified, plated through and connected to the inner layers. In this, the entire PCB is copper plated. Then the plugging paste is applied. After curing, the PCB is resurfaced in order to recreate a flat surface. In this process, a few μm are also eroded. Then the remainder of the drill holes are introduced into the PCB and plated through . The PCB is again copper plated at the same time. Then the PCB is structured.However, this procedure is problematical for blind vias, as air inclusions during the application of the plugging paste are possible. During the soldering process, this may lead to delamination. Work stages
17.5 – Advantages and disadvantages at a glance
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