Box build assembly is an important aspect of the electronics manufacturing process. It requires manufacturers to deliver a complete ready-to-use product to the market, providing a seamless experience for different users. Box build assembly is more than just putting the parts together, it involves careful design, a precise box build assembly process and strict subsequent quality control to ensure that the final product meets the required specifications and standards.

What is Box Building Assembly? 

Box build assembly refers to the process of assembling various required parts into a final product. It can consist of one or more PCBs with mechanical components like busbars, stand-offs, screws, tags, terminals, sealants, pressure vents, etc. External electricals like harnesses, cables, sockets, in-wire chokes, Panel mount connectors, high current wires, thermal pads, etc., are also part of it. The box build assembly enclosure is made up of types of plastics or metals or a combination of both based on the applications. Box build assembly for SMPS circuits, inverters, servers, etc have heatsinks on one or more phases of the casing for effective heat dissipation.  Box build assembly is not just working around the enclosure for a system but the factors revolving around it to make it compact, functional, utility, and feasibility solutions. 

The Main Box Build Assembly Process From Concept to Completion

To design and create a concept of box build there are various subsystems and sub-assembly associated with the box build assembly process. These things have to be designed and developed according to the requirements and constraints of mechanical and electrical accepted. The major classifications are box build design, subassembly components, PCB assembly, wiring harness, integration, and Quality.

Conception and Design

 The brand owner or the final user will raise a conception of the electric box build, both mechanically and electronically. Then designers will get this concept into drawings. 

• Bom files mean a bill of materials files. All the necessary materials will be listed in the files, such as PCBs, wires and cables, components, metal parts, enclosure etc. 
• PCB Gerber files are the files used in PCB fabrication. PCB is the backbone of all electronic products, and it is critical for a successful box build assembly. 

Subassembly Components Preparation

Before the box build assembly process, all the subassembly components need to be prepared properly according to the BOM (Bill of Materials) list in the design stage. Close attention should be paid to the classification, sizing, allocations, and customization of all the mechanical components. 

• The main factor for any box build assembly is the power supply as the number of components is more and the size of these components is significantly high.

• Storage devices are also comparatively huge, for example, CPUs, laptops, etc. These storage devices also require some coolant fans which also have to be considered in the box build assembly process.

• Industrial, commercial, and automotive assemblies have a keypad, I/O panels, Display modules, Keypads, and assembly mounts which are essentially a part of a panel in the box build assembly.

• Complex internal harnesses that connect power blocks, peripherals, displays and other interconnects are important. The design requirements have to be met with the length and dimensions of the cable. Most of the harnesses are shielded and routed inside the box build assembly with a guard. 

PCB Assembly

• PCB assemblies are done on mounts or standoffs in general. If the PCB dissipates heat, then it is mounted on a heatsink or stand-off with a coolant fan or liquid-cooled plate underneath it. 
• Slot mounting, rail mounting, and adhesion to the plate are also practised in a few box build assembly applications. 
• High power PCB or Heat dissipating PCB are mounted on the heatsink after applying thermal gel or thermal pad. 
• Guarding for assisting PCB position is designed on the plastic casing. The harness on the inter-system PCB has to be routed with specifications like a shield, twisted pair, cable chokes, etc based on the application demands.
• In a box build assembly process, PCB designing does not just focus on the design, feasibility, cost, and reliability but also on feasibility inside the subsystem, mechanical mounts, positioning, and verifying the component clearance with the 3D body. Clearance across the components can also be verified and set as per standards. 
• Vibration and heat dissipation for PCB is simulated and tests are done during the prototyping stage to ensure there is no failure mode during the full performance of the system for a set time. 

Cable and Wiring Harness 

• To interconnect PCBs inside the enclosure wires, cables, flex cables, and receptacles are used.

• To hold the routing of wires to the frame or casing ducts, raceways are used and to hold the bundle of cables zip ties are used or sheath enclosure.

• Mounting the receptacle should be feasible and the lengths of the routing should also maintained with short distance. 

• Generally, harnesses are categorized into signal or communication lines and power lines. Both the signal and power lines are not routed together unless there are any constraints, this ensures stability in signal integrity.

• The harness of systems is complex and therefore labeling of the signal and power lines is done on both ends of the terminal. 

• Cables passing through the casing are mounted using cable glands. These cable glands should not be small enough to put stress or strain on the cables and must not be loose to provide a breach Ingress Protection rating. 

• Cables are also accessed outside the panel if a panel mount connector is used, this is used in most of the closed commercial systems.

System Integration

• Accessories like buttons, keypads, and displays are installed on the mounting plates, and handles.

• Pressure vents for IP6x-rated subsystems and air vents are designed appropriately. 

• The majority of the box build assembly is provided with a cooling fan or liquid-cooled system for Electronics demand.

• Dampers, rubber feet, and panel covers are also installed in the process.

• Box build assembly has its own business development arc with logos, graphics, and design features as a part of branding and marketing elements.

• Safety checks in the box build assembly process like Warning signs, text labels, and compliance markings are engraved on the PCB as per standards.

• Traceability elements like QR, Bar code, Component number, or tracker number are printed on top of the assembly.

Quality Control

• Testing and maintaining the quality consistently in the box build assembly process is the prime factor.

• The functional testing system identifies the preprogrammed testing of electrical functions like short circuits, leakage, insulation, and Surge.

• Firmware and software flashings are tested with boot-up, peripheral reading, terminal interface, etc.

• Operational testing, switch testing, vibrations, and temperature are the next set of tests that are proceeded with.

• Safety and compliance standards like UL, CCC, CE, FCC, VCCI, and ROHS are followed.
• Box build assembly has its specific tests like a visual inspection for fit and finish, calibration of electronic components, a burn-in test is nothing but continuous testing by prolonged operation, thermal testing to monitor the box build enclosure temperatures, pressure test, drop test, shock test, vibration test are also done based on the demand of the sub-assembly.