Desde prototipos de circuítos en placas de pan ata o deseño dos nosos placa de circuíto impreso (PCBS), it was like getting off the training wheels. There’s a lot to learn about this process, so let’s get started. O deseño de PCB lévase a cabo nun proceso de enxeñaría eléctrica (EE). EE crea o “cerebro” de como funcionan os dispositivos. Without electronics, you’re left with little more than a pile of metal and plastic.

Things to know before starting PCB design: 1. PCB size – this depends on your product size (or case size). As dimensións do produto defínense durante o proceso de deseño de enxeñaría electrónica. You can watch a video about it here. 2. Capas de PCB: cantas máis capas, máis complexa é a FABRICACIÓN do PCB. (Nota: Incluso un PCB dunha soa capa pode ser un PCB complexo, pero aquí estamos falando da complexidade de facer un PCB. Cantas máis capas teña un PCB, máis caro é fabricar.)

Layer 2 is usually used for simple toy products

Os produtos relacionados con IOT adoitan ter 4 capas

Typically used for floors 6 to 8 of a smartphone or smartwatch.

3. Your PCB manufacturer’s requirements. Be sure to read the guidelines for rhythm, trace size, power isolation, and file naming before you start designing.

Información que debes proporcionar aos fabricantes de PCB:

Number of layers (e.g. 2, 4, 6, etc.)

Materiais (FR-2 (papel de algodón fenólico), FR-3 (papel de algodón e epoxi), FR-4 (fibra de vidro e epoxi … Etc.)

Thickness (0.5 mm, 1.0 mm… Etc.)

Color (red, black, green… Etc.)

Tratamento superficial (ENIG (inmersión química en níquel / ouro), DIG (inmersión directa en ouro), OSP (conservantes orgánicos soldables, etc.)

Copper weight (1 oz (35 microns), 2 oz (70 microns), 0.5 oz (18 microns)… Etc.)

Ficheiro Gerber

PCB design process:

Deseño de circuítos

For this step, you need to create the schematic. This is a document, like a blueprint, that describes how components relate to each other and work together. To create the schematic file, you will need a software tool. We like Quadcept because it is optimized for designing PCBS for manufacturing (for example, you can export a Bill of Material (BoM) directly from the tool) and is cloud-based, so it can be easily used anywhere. (They also offer a free community version of the tool for manufacturers and students.)

There are many other options you can choose from:

Altium

ExpressPCB

Dispositivo de frecuencia

KiCad

Cadence allegro

Comida

Deseño asistido por ordenador

DipTrace

After you install the selected tools, you need to obtain the component specifications for each selected component. They can often be found on the supplier’s website. O ficheiro modelo axudarache a debuxar o esquema. This component becomes available in the database when you upload the model to the software tool. Then, all you have to do is follow the data manual and connect the wire to each pin in the component. (Nota: os detalles do proceso de deseño dependerán da ferramenta de software escollida).

Each schematic symbol needs to have an associated PCB space area to define the physical dimensions of the component and the location of the through holes on the brazing pad or PCB. You should have selected the components (or are now selecting them), and we describe this process in the EE Design Process video (see video).

Example diagram

A good schematic is really important, as it will be used as a reference document during debugging and is a good communication tool with other engineers. Ademais, o fabricante pode probar o dispositivo a través dos puntos de proba deste documento.

PCB layout + Gerber file

To design the PCB layout and create Gerber files, you can use the same software tools we mentioned in circuit design. A diferenza dun esquema, un deseño de PCB asigna os compoñentes reais ás localizacións exactas do PCB e mostra as pistas que conectan cada compoñente entre as capas do PCB. As mentioned at the beginning of this article, the more layers, the more complex the manufacturing required, and the higher the cost.

Divide the PCB into logical parts based on functions (e.g. power supply, audio output, etc.). Then, be sure to group the components of each section into the same area. Deste xeito, pode manter o rastro condutor curto e reducir o ruído e as interferencias.

Tamén hai que ter en conta a interface de usuario (IU) ao deseñar un PCB. Compoñentes como tomas de audio, conectores, leds, etc. deben axustarse para conseguir a mellor experiencia de usuario.

Once the layout is designed, a Gerber file is generated. Your PCBA manufacturer will use this file. Hai moitas empresas que ofrecen estes servizos e desde a biblioteca experta de HWTrek recomendamos a Kingbrother, NexPCB e HQPCB.

Sample Gerber files

A colocación de compoñentes no PCB é moi importante. Some components can interfere with each other and cause unexpected behavior. For example, if you have both Bluetooth and Wi-Fi modules, they have the same 2.4ghz bandwidth and can interfere with each other if incorrectly placed.

PCB production

When you send the Gerber file to the PCB manufacturer, they can print the board. Esta será a base para seguir construíndo a base para engadir compoñentes ao PCB e fabricar o PCBA (conxunto de placas de circuíto impreso).

Unassembled PCBS

PCBA (Assembly)

Preparación de materiais

Neste punto do seu deseño EE, debería ter seleccionado os compoñentes. You can ask the PCBA manufacturer to order the required components for you, or do it yourself if you choose a supplier. Asuntos que precisan atención

Lead time: As these components come from different suppliers, keep the lead time in mind. For some components, it can take up to 8-16 weeks.

Packaging: Order components from reels that are automatically picked up by SMT machines instead of packaging them individually.

Minimum order quantity: Check the minimum order quantity of the component. Se compra menos do mínimo, asegúrese de que os compoñentes seleccionados estean en stock. For small batches (up to 50), you can order online from DigiKey or Mouser. Para obter máis cantidades, consulte co seu fabricante.

Loss: Order 10% more to cover loss (not for expensive components)

Install components on the PCB

There are two main ways to place components on a PCB surface:

Through-holes (through-holes) are manual methods of assembling assemblies with wires into holes on the surface of a PCB. It is also commonly known as DIP or dual in-line packaging process. (See SMT in progress in this video)

A tecnoloxía de montaxe superficial (SMT) é o método máis utilizado na produción en masa. It is done by fast, accurate SMT machines that save you time, money and avoid human error.

Cousas para recordar:

Your component type number must not exceed the number of reels that the manufacturer’s SMT machine can support.

Optimize and consolidate your components so that only one SMT runs.

Check manufacturer supported footprint pad sizes. Otherwise, the SMT machine will not install components correctly.

Some larger components cannot be installed by machine and still require manual through-hole work. Therefore, both technologies can be used on the same board.

Any components you need to manually add via the through-hole method add to the manufacturing cost.

Reflow soldering

A soldadura por reflujo é o proceso de facer que os compoñentes se “peguen” ao PCB. The PCBA heats the circuit board through a reflow furnace or an infrared lamp until the solder melts, thereby permanently attaching the component to the circuit board.

The trickiest part here is not to overheat or damage the components, because the thermal characteristics of each package are different. Un fabricante fiable de PCBA será o responsable deste proceso e todo o que cómpre facer é proporcionarlles as especificacións dos compoñentes.

Reflux process.

Other welding methods:

Wave soldering is mainly used for manually added components by the through-hole method. Neste caso, o PCBA pasará primeiro polo forno de soldadura por refluxo e, a continuación, engadirá outros compoñentes manualmente despois de pasar pola máquina de soldar por ondas.

A soldadura de ferro pode usarse para situacións específicas, pero non para a produción en masa.

Probas e inspección de calidade

Neste paso, as mostras de PCBA probáronse para garantir a calidade. Os erros máis comúns son: curtocircuítos en compoñentes desconectados, compoñentes mal aliñados e partes do circuíto que non deben conectarse. As probas máis comúns:

TIC (probas en liña). When designing a PCB, some test points are usually reserved for debugging, programming, and other purposes. A máquina TIC empregará estes puntos de proba para probar circuítos abertos / curtocircuítos e comprobar que os valores dos compoñentes pasivos (resistencias, indutores, condensadores) están dentro do rango de especificación.

AOI (inspección óptica automática). Manufacturers use a “gold sample” (reference PCBA) to compare with other samples. Para esta proba, o creador de hardware deberá proporcionar especificacións e tolerancias ao fabricante para establecer os parámetros.

Raios X. The PCBA manufacturer will use X-rays to check the welding conditions of the BGA (ball Grid Array) components. Mira a proba de raios X neste vídeo.