The Impact of Vias on PCB Assembly

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The continuing trend towards smaller and smaller devices with even more functionality has resulted in a dramatic reduction in the size of components, silicon packages, and the PCBs themselves. Component technologies such as BGAs and CSPs have challenged PCB manufacturing technologies due to the number of input/output connections and tighter and tighter pitches associated with these devices. Don’t forget the costs associated with fabrication.

Via technology—including blind and buried—has been one of the solutions to address the miniaturization and component density challenges in current electronic assemblies. Advantages include improved electrical and thermal performance; increased wiring density; space-saving in PCBs; placement of even more chips and components in PCBs; and finally, smaller PCBs.

Source: I-Connect007 Survey

However, vias are not without their own set of challenges. In our recent survey that focused on vias, respondents mentioned challenges such as impedance matching, routing, placement of vias, minimum size limitations, aspect ratio, and the limitations for the PCB manufacturer. One respondent commented: “In-pad vias in thermal pads and regular lands often cause processing issues. If they are tented, trapped residues and ‘popping’ are issues. If they are not tented, solder thieving is an issue. We have also tried using solder mask dams on the pad to prevent thieving with poor results. We also don't want to add more vias than necessary to meet the thermal target. In this case, more is not necessarily better as it may increase voiding at the thermal interface.” He added that more vias increase the drill time at the PCB fabricator side, and may increase cost.

Reliability is also an issue, per our survey. One respondent said that their QA department is concerned that tenting vias leaves contaminants in vias, which can affect the long-term reliability of the PCB assembly. He noted, though, that tenting vias help minimize solder problems, so he always tents vias. Apart from tenting, via filling, mask covering and plating are also challenges when dealing with vias.

To read this entire article, which appeared in the November 2016 issue of SMT Magazine, click here.