It is a common desire to avoid buying an electronic device only to experience its malfunction just after a week of usage. We have been using the same LCD monitor for more than five years now. We can confidently say that it is one of the most resilient electronic equipment we have ever possessed. If you value dependable products, you are likely to take note of industry standards aimed at enhancing the lifespan of electronic devices.
The reliability of Through-hole plating in the printed circuit board is essential. It ensures the plating can endure shock & thermal cycling. That’s why plating processes play a vital role. The latest plating standards in IPC 6012E mandate the use of strategies that enhance the dependability of VIP structures.
Structure of Copper Wrap Plating
To establish signal connections between films in the multilayer printed circuit board, via holes in filled via-in-pad structures must undergo copper plating. This plating enables connections to other Contact points within VIP structures and directly to a trace via a small copper ring. Although indispensable, these structures are prone to reliability issues during thermal cycling.
In compliance with IPC 6012E, via-in-pad structures must undergo copper cover plating. It entails filling the copper plating around the perimeter of the through-hole & extending it onto the annular ring encircling the via pad. This mandatory procedure enhances the durability of the through-hole plating. It may minimize failure resulting from cracks or the detachment of surface features from the plated through-hole.
There are two types of filled copper cover structures. The first type involves the application of a copper film to the interior of a through-hole. It then covers the bottom and top films at the via ends. This wrapping of copper plating serves as the through-pad & trace that leads to the through-hole, creating a copper structure.
On the other hand, the through-hole is equipable with a distinct pad layer that forms around its ends. It connects to either traces/ground planes. In this case, the copper coating that fills the through-hole covers the upper part of the outer pad. It results in a butt joint between the via pad & copper plating. Although there is some bonding between the via pad & fill plating. The 2 don’t merge or create a unified, continuous structure.
Reliability of Copper Wrap Plating Under Thermal Cycling
During the thermal cycling of a PCB, the copper cover plating, fill material, and laminate interfaces experience tensile stress. It is due to volumetric expansion. Various factors, such as the temperature gradient between the board determine the magnitude of this stress.
When the thermal expansion coefficients of board materials do not match, it can result in notable stress on the copper cover plating. It leads to cracks & separation in the through-hole barrel and butt joint. At the end of the via, the continuous copper cover plating may also experience cracking at the correct angle.
When the Internal of the through-hole detaches from the square joint, it results in a circuit failure. With continuous thermal cycling, you can expect more failures to occur as the board flexes. Vias that terminate near the outermost layer of the circuit board are at a higher risk of fracturing under temperature cycling because these layers tend to experience more significant flexing.
Although there is a risk of failure in the structures, copper cover plating remains more dependable than vias without it. The additional layer of covered copper reinforces the structural integrity of plating in a through-hole wall. It enhances the contact point between the through-hole plating & annular ring.
To enhance structural integrity, manufacturers may add cap plating over wrap plating. This process involves applying plating on the top & bottom sides of the through-hole, similar to the wrap plating. After stripping the plating opposition, load the through-hole with epoxy, and planarize the finish to create a smooth finish. This approach is the most effective way to optimize reliability while satisfying the IPC-A-600 Acceptability of Printed Boards.
It is feasible to apply IPC 6012E plating to buried vias. It provided that the buried through-holes are divided into some layer stacks. So the inner film stacks are plated using copper wrap plating, similar to vias. Each stack can be plated, and a prepreg can be utilized to organize the last stack up. Vias located on interior layers are plated just like vias.
Multilayer PCBs and Copper Wrap Plating
Multilayer PCBs play a critical role in the design of electronic systems. It ows to their numerous advantages such as being lightweight, offering high assembly density & compact size. By consolidating multiple PCBs onto a single board, multilayer PCBs can meet the stringent weight & space requirements of contemporary product development.
The construction of multilayer printed circuit boards involves a crucial element known as the through-hole structure. It connects the pads, traces & polygons across various films of the printed circuit board. The use of copper cover plating is a significant aspect of via construction in multilayer printed circuit boards, as it enhances the dependability of VIP. The focus of this article is to delve into multilayer printed circuit boards via(through-hole) structures & copper cover plating.
Via Structures & Copper Wrap Plating in Multilayer PCBs
Copper cylinders, or vias, are inserted or created in drilled holes on a printed circuit board (PCB). Vias act as connections that unite pads, traces & polygons on various coatings of the multilayer printed circuit boards, serving both electrical and thermal purposes. Particularly in multilayer printed circuit boards, vias are essential in achieving a desirable component density. Including vias facilitates the interconnection of traces & components between different layers of a multilayer PCB. These structures enable the transfer of both power & signals across the layers. Additionally, incorporating vias simplifies the routing procedure.
Types of Copper Wrap Plating or Via Structures
The various kinds of vias present in multilayer circuit boards are classified as:
- Through-hole via – The function of these vias is to establish a connection between the outer layers of the board by running through its entirety. If this via is coated with a conductive substance like copper, it transforms into a plated via, whereas if left uncoated, it is referred to as the non-plated via.
- Blind via – Blind vias are the connections between an outer layer and an inner layer.
- Buried via – Vias that establish connections exclusively between the interior coatings, without extending to the exterior coatings, are known as buried vias.
Regardless of the type of via structure, copper plating is essential to create a dependable via.
Copper Wrap Plating
In circuit board manufacturing, copper is important. It is extensively available on the layer planes of PCB and over the sides of via. Depending on the type of via, the placement of copper may vary. Through-holes have copper on the surface layer, while vias has copper in form of pating.
Copper cover plating is a type of electrolytic plating that extends from the plated through-hole structure to a finish of a printed circuit board. During the circuit board fabrication process, copper is inside the drilled through-holes, covering the copper annular ring on both the top & bottom surfaces. This plating process is continuous and envelops the shoulders of the plated via, providing an electrical connection between the top & bottom layers of the PCB.
IPC standards, including IPC 6012B & 6012E, define the copper cover plating & plating thickness requirements for all loaded plated vias. These standards categorize electronic designs into three classes: class one for general products, class two for dedicated electronic products & class three for high-reliability products.
Design to Fabrication & Manufacturing
To ensure a smooth fabrication & manufacturing process for your circuit board, it’s important to have the necessary software to communicate your board & parts information precisely. The last thing you want is for your design process by the need to search for the new supplier who can meet your specific requirements.
By utilizing an effective bill of materials, you can provide your partners & vendors with concise part instructions. In addition, coupling your design software with output files & materials bills can streamline the fabrication process, ensuring precision and ease of production
Altium Designer, exceptional printed circuit board design software, simplifies the process of defining your coating stack up, plating & designing the vias for your multilayer printed circuit board. With its top-notch capabilities, Altium Designer assists in designing devices that comply with the standards of IPC.
