PCB & SMT Assembly
Nordson Electronics Solutions offers precise dispensing, jetting, and conformal coating solutions to meet the many demands of printed circuit board assembly
Overview
PCBA
Nordson Electronics Solutions has been a leader at every point in the evolution of fluid dispensing for printed circuit board assembly (PCBA), also called surface mount technology operations (SMT), from early time/pressure pumps and auger valve systems through today's jetting technologies and closed-loop process controls, providing many options for balancing speed, volume control, precision, and price.
Failure Protection with Underfill
Many large components, such as Package-on-Package (PoP), ball-grid arrays (BGA), and chip-scale packages (CSP) require underfill to prevent failures. Small, narrow fillets are needed to meet tight keep-out-zone (KOZ) requirements on densely populated boards. Quality, speed, and productivity are additional critical components to consider when applying underfill to these components.
RF Shielding with Metal Cap Attachment
RF shielding is required for mobile devices and automotive sensors to prevent interference. Metal caps are commonly used but require selective soldering with LTS (low-temperature solder paste). Fast, precise solder paste can be used to dispense unique cap shapes, eliminating the need for metal cap attachment.
Heat Dissipation for Hot Components
Many high-speed processors, AMPs and converters/inverters need efficient heat dissipation. Thermal interface material (TIM) plays an important role to transfer the heat from the components to the heat sink or outer case. Although there are many various TIM types such as grease, gel, paste, pad, metal pre-form, and phase change, many components requiring high heat dissipation use fluid types like grease, gel and paste because of their better thermal conductivity. Exact volume, thin profile, wearing resistance (TIM is abrasive), and productivity are the key performance factor for TIM dispensing. CPJ/MFC, dispense gap control in z axis, the right consumable combinations and speed are suitable to this application.
Moisture Protection with Precise Conformal Coating
Mobile electronic devices are used everywhere, for example texting in the shower room. Electronics must be protected from moisture by a thin, uniform polymer coating, known as conformal coating. But the electronics have many interconnections outside the device, and many different form-factor components (tall and low). Conformal coating needs to avoid some sections and reach into some hard-to-reach areas; this process is referred to as selective coating. One of the key performances for conformal coating equipment is this selectiveness and the process controls that can enhance the application. Film coating, atomized coating, applicator or valve rotation and tilting as well as other features address these conformal coating challenges.
Another challenge is that the target components are so small that conventional spray conformal coating will not work. There are many flex circuits with tiny components in mobile devices, like 01005 capacitors that have to be coated individually. Jetting technology addresses the challenge and applies that precise coating.
Surface Mount Adhesive (SMA) for Component Reflow
During reflow, surface mount technology (SMT) assumes components stay in the right place even if they are on the backside. Surface mount adhesive (SMA) plays an important role by holding the components in the right place on the PCB. These components are often allocated sparsely on a large board. For productivity, dispensing heads are required to move fast between these sparse points, and shouldn't waste time moving up and down for SMA fluid break-off. Jetting technology and faster dispensing platforms are key features for this application.
Key dispensing applications to serve these PCBA challenges are:
- Solder paste sealing for RF shielding
- Underfill jetting, 2nd level, for BGA, CSP and PoP
- TIM dispensing for heat dissipation
- Conformal coating for moisture protection
- SMA jetting for component reflow
Plasma PCB Manufacturing
In printed circuit board (PCB) manufacturing, plasma technology can deliver higher uniformity and reproducibility than chemical or mechanical processes and help improve reliability. It is efficient, economical and environmentally benign. Plasma processing increases the surface energy of advanced materials, including fluoropolymer, providing excellent lamination and wettability for plating through-holes without the use of wet chemicals. It also allows metalization to the inner layers by removing resin smear created in the drilling process and removes carbon byproducts from blind vias.
Desmear & Etch Back - The mechanical drilling of vias in multi-layer PCBs creates a residual resin that smears along the via walls, impeding metalization of the electrical connections. After drilling, resin removal from inner layer posts is required to ensure reliable electrical contact. Traditional methods of etching and desmearing are often not effective due to the capillary effect present with wet chemicals, and the limitations related to the use of advanced board materials. In contrast, plasma effectively removes epoxies, polyimides, high Tg blends, mixed materials, and other resins in standard and high aspect ratio panels.
Non-Stick Surface Activation - The Nordson MARCH plasma process can modify fluoropolymer surfaces and desmear resins to prepare hole walls for electro-less copper or direct metalization. Surface activation for double-sided and multi-layer fluoropolymer through-hole boards is necessary to increase surface wettability.
Carbon Removal - Plasma treatment removes carbon from both conventional through-hole board vias and blind vias. Laser-formed vias often produce a carbon by-product that prohibits electro-less adhesion. Carbon that mixes with epoxy or polyimide resin and becomes trapped in the vias must be removed prior to metalization. Plasma cleaning removes the carbon from both conventional through-hole board vias and blind vias typically used on boards where component space is restricted.
Inner Layer Preparation - Plasma alters the topography and wettability of inner printed circuit board layers to promote adhesion. Cover-coated inner board layers that contain flex materials with unsupported polyimides have smooth surfaces that are difficult to laminate. Plasma alters the topography and wettability of the inner layers to promote adhesion by allowing thin layer processing through use of flex clips. Other chemical processes are not as effective: it is difficult to control the amount of material removed, and unsupported polyimides are inert to most chemicals.
Residue Removal (Descum) - Plasma treatment removes resist residue from PCB inner layers and panels without affecting the circuit pattern. It also removes residual solder mask bleed from lands for better bonding and solderability. Resist residue sometimes remains after developing fine pitch circuitry. If the residue is not removed prior to etch, the board can short circuit. Plasma effectively removes resist residue from inner layers and panels without affecting the circuit pattern. It also removes residual solder mask bleed from lands for better bonding and solderability.