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Connect the Dots: What Designers Should Know About Non-conductive Via Fill

The rapid advance of technology is driving changes in electronics that require increasingly smaller boards capable of handling higher signal speeds and supporting more robust software applications.

Manufacturers are increasingly called upon to produce ultra high density interconnect (UHDI) PCBs, so it’s important to tune our production capabilities and customer service models to this trend. Non-conductive via fill (NCVF) offers a cost-effective, reliable manufacturing method that accommodates the densely packed, fine-pitch ball grid array (BGA) components present in UHDI designs.

Not all PCB manufacturers approach NCVF in the same manner. Designers who thoroughly understand the process will have more confidence that their designs will be manufactured to meet requirements.

Benefits of Non-conductive Via Fill
Primarily used to prevent solder wicking into vias, NCVF is the process of filling drilled holes with a specialized, non-conductive, low-shrinkage epoxy. Boards can have a higher component density because manufacturers use a technique called via-in-pad, plated over (VIPPO). This involves placing a via used to conduct signals between layers into the same real estate as a surface mount pad. VIPPO eliminates the need to route a trace from the component lead to a via nearby, provides a nice flat pad for assembly, and prevents solder from wicking through the via and weakening the solder joint. 

The epoxy inside the holes makes the vias more reliable by limiting expansion during heat exposure. It enhances mechanical strength, prevents solder wicking into vias, and enables via-in-pad technology. By filling voids with epoxy, vias are sealed and protected from contaminants. NCVF creates superior structural integrity against stress fractures compared to conductive fills and offers a better coefficient of thermal expansion (CTE) match with the surrounding laminate. 

Submitting a Quote: Manufacturer Capability and Process
What do designers need to know? First, can the manufacturer accommodate your needs if you call out NCVF for a design with smaller pitch components? Manufacturers often publish specs that inform designers of their capabilities, making it easier to assess them before submitting a quote. 

If a manufacturer does not make it clear, contact them directly to confirm they have experience with NCVF. Manufacturers unable to meet design requirements in-house may still provide a quote, either to engineer NCVF capability on the fly or to farm out production to a subcontractor. 

This can create challenges with lead times and yield, and potentially jeopardize production of the boards. Designers should clearly define the non-conductive via filling requirement in the Gerber files and confirm the manufacturer has the proven ability to build the PCB to specs. 

More information is always better when submitting quotes. We encourage designers to include as many specifics as possible in their quote requests. This can include specifying non-conductive material used for via filling, identifying the type of surface finish needed to ensure a flat pad for assembly, and defining any other key manufacturing considerations.

Working Closely With Your PCB Manufacturer
When designers call out production specifications in detail, manufacturers do not have to guess what the designer wants. Collaboration also serves to minimize ambiguity about expectations during the quote process and before PCB manufacturing takes place. Open communication helps the designer and manufacturer align priorities based on what is required at any given stage of the lifecycle, from early prototyping to final prototype to full production.

Collaboration also helps the designer understand the experience level and capabilities a manufacturer possesses regarding a capability such as NCVF. Not all manufacturers take the same approach to the process. Don’t be afraid to ask to speak to members of the production team. Doing so can help you better understand the manufacturer’s approach and align expectations for things like lead time, cost control, and board functionality. Talking to individuals on the production floor, such as engineers or team leaders, will give you more confidence in the manufacturer’s ability.

The more designers know about a manufacturing technique like NCVF, the better they can craft quotes that ensure their designs are built to spec. 

Breaking down the NCVF process

If you’ve had a chance to read my columns or my book about designing for the reality of PCB manufacturing, you know I think it’s important for designers to have a good working knowledge of each stage of the manufacturing process. This knowledge can be quite useful both during design and when it is time to create a quote request for your manufacturer.

Following is a high-level breakdown of the NCVF process:

1. Drill the holes that require via filling. 
2. Clean the holes to remove any debris present from the drilling.
3. Plate electroless copper across the entire panel and inside the holes to provide connectivity within the holes for electroplating.
4. Electroplate ~0.5 mils of copper across the panel and into the holes.  
5. Laminate photoresist and image for button plating. This exposes just the holes and a little more of a pad on the surface.  
6. Button plate. Plate another ~0.5 mils of copper into the holes. Remove the resist.  
7. Planarize the buttons off the surface of the panels.  
8. Using vacuum filling or screen printing, force non-conductive epoxy into the via holes.
9. Thermal cure the epoxy. 
10. Sand the surface of the panels to remove any via fill epoxy and copper buttons on the surface. This surface planarization restores a flat copper surface.
11. Parts from here are returned to drill to have the rest of the holes drilled and panels follow standard manufacturing process.

Matt Stevenson is vice president and general manager of ASC Sunstone Circuits. To read past columns, click here. Read Matt’s book, The Printed Circuit Designer’s Guide to … Designing for Reality and listen to his podcast series here.

This column originally appeared in the May 2026 issue of I-Connect007 Magazine.