Nordson ASYMTEK 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.
Drop Failure Protection with Underfill
Many large components such as Package-on-Package (PoP), ball grid arrays (BGA) and chip scale packages (CSP) on mobile device board require underfill to avoid failures from dropping. These components are allocated very tightly to each other. The keep-out-zone (KOZ) is the key parameter to distinguish quality underfill dispensing: a small underfill fillet from the component edge to other components is desired for tight allocation. Dispensing small volumes of underfill closer to the components is required, which requires the dispensing system to deliver small dot volumes to very accurate locations. Moreover productivity is critical, so jetting speed contributes to it.
RF Shielding with Metal Cap Attachment
Mobile devices include many wireless components that have to be covered by RF shielding to prevent interference. Metal caps are most common for RF shielding where the caps cover components separately. But attaching the caps on board requires selective soldering with low temperature solder (LTS) paste: secondary soldering. Faster and precise solder paste dispensing for unique cap shapes is the key to productive and high yield 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 type 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