PCB Assembly Guide

Cost reduction tips

Especially for new designers, it is necessary and important to learn the guidelines to save cost for your first prototype PCB manufacturing

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PCB Assembly Guide

Cost reduction tips

Design for Manufacturing and assembly are the integration of product design. The aim is to design a product that can be easily achieved and can be manufactured in a economic way. so there are some guidelines or tips which can be considered.

Especially for new designers, it is necessary and important to learn the guidelines to save cost for your first prototype PCB manufacturing.

Cost reduction tips

Circuit Board Material

The circuit board foundation, sometimes referred to as the base, comprises the substrate (or core) and the laminate. The substrate is the non-conductive dielectric material, typically chosen based upon the dielectric constant, dk. Laminates when used in conjunction with substrates provide the copper foil or surface material. However, laminates may themselves be used as core material in some board constructions.

Substrates

Substrates are typically dielectric composite structures that are comprised of epoxy resin and paper or glass weave (sometimes unwoven), which may be supplemented by ceramics to increase the dielectric constant. Substrates are made to meet certain property requirements, like the glass transition temperature (Tg), which is the point where heat causes the material to deform or soften, and may be customized. However, there are a wide variety of standard substrates from which the majority of PCBs are fabricated. These include FR-1 thru FR-6, CEM-1 thru CEM-5, G-10 and G-11, Aluminum or insulated metal substrate (IMS), Polytetrafluoroethylene (PTFE), RF-35, Polyimide, Alumina and flexible substrates Pyralux and Kapton. FR-4 is by far the most commonly implemented of these substrates.

Laminates

Laminates are manufactured under pressure and consist of cloth or paper layers and thermoset resin. Just as with substrates, laminates can be made to meet custom requirements or properties. Properties of interest for laminates include tensile and shear strength, the coefficient of thermal expansion, CTE, and Tg. Dielectrics commonly used for laminates include FR-1, FR-4, polytetrafluoroethylene (Teflon), CEM-1 and CEM-3. Also common are pre-preg materials FR-2 thru FR-6, CEM-1 thru CEM-5 and G-10.

Together the substrate and laminate define the basic electrical, mechanical and thermal circuit board properties that, when used in conjunction with an accurate board type, enable you to make the best selection of PCB material for your design.

Circuit Board Types

Circuit boards may be classified in a number of ways:

Classification Criteria

  • component location – single-sided, double-sided, embedded
  • stackup – single layer, multilayer
  • design – module-based, custom, special
  • bendability – rigid, flex, rigid-flex
  • strength – electrically strong, mechanically strong
  • electrical functionality – high frequency, high power, high density, microwave

The first three criteria above are poor candidates on which to base your selection as they are not based on circuit board material properties. While bendability and strength are good physical criteria, they do not provide guidance on your board’s ability to function as desired. Electrical functionality is based on PCB function, which makes it a good criterion for design-based circuit board material selection. According to function, PCBs may be classified as the following board types:

  • High Frequency (High Speed) – These boards can accommodate frequencies in the 500MHz – 2GHz range.
  • High Power (High Current) – These boards must be able to carry high currents, which usually requires wider traces and thicker copper, withstand and effectively dissipate high temperatures.
  • High Density (High Density Interconnect) – Typically complex, these boards have thin traces, utilize laser microvias and thin high-performance materials.
  • Microwave – Microwave boards usually refer to PCBs where signal speeds from 1GHz to hundreds of GHz are present; however, the microwave spectrum actually extends from 300MHz to 300GHz.

The board types above can be used to select the circuit board material best suited for your design.

For any designs for manufacturing, the important design principles or rules is to help the designer or developer reduce their cost or reduce the difficulty of manufacturing of the PCB, and here below are a listing of these principles. The following are some suggestions or tips for designers to make a cost-effectively printed circuit boards.

As a matter of fact, about 60%-75% of manufacturing costs of the PCB or other products (quality of materials, production processing, and products assembly, etc.) are determined by design decisions. so it makes the designs so important for your projects in a cost effective way.

1. Reduce Amount of Parts

Reduction of the amount of the parts or components is a good chances for reducing the manufacturing cost, less parts means less purchases, processing time, assembly difficulty, testing etc. It ease the processing process and in 90% it can reduce the assembly cost. In general, it reduces the level of intensity of all process related to the final finished product during its processing life.

2. Use Standard Components

The standard components are normally in stock and easily sourced. resistors, capacitors in 0603,0204, which are easily purchased in many different channels. Standard components are less expensive than custom-made items due to the cost in delivery, customs etc in custom-made components.

What’s more, the high availability of these components reduces product lead times. As we all know, it will charge tax for the customized components or imported components, and some are forbidden in local market, absolutely it will cause extra cost to your final products.

Some Tips on PCB Design for Cheap Manufacturing
Some Tips on PCB Design for Cheap Manufacturing

3. Design for Ease Fabrication

Some designs are with special requirements, in very strange shape,with many slots or v cut lines, In general, excessive tolerance, surface-finish requirement, very small hole size, small track space, or heavy copper weight and so on are commonly found problems that result in higher than necessary production cost.

Select a good combination between material and design of fabrication process to minimize the overall manufacturing cost.

For example:

  • Hole: normally 0.3mm is standard hole size, and hole below 0.3mm will lead to higher cost. Any buried vias, blind vias, half holes will also cause higher cost.
  • Track space: standard is 6/6mil, 5/5mil or below will increase cost.
  • Surface finish: HASL with lead is the cheapest, if make in immersion gold, it will have extra cost $22-$23.
  • Solder mask color: green solder is most commonly used color for PCB, therefore it is the cheapest, and other color, like Matt black, red, yellow will increase cost.

Selecting the Best Circuit Board Material for Your Board Type

As stated above, there are a number of physical characteristics or properties that can be used to identify circuit board materials. These characteristics are important and may be used for in-depth substrate and laminate analysis. Additionally, they may be used as metrics for comparison, which is done below. In the following table, common substrates and laminates used to form the foundation of PCBs are compared according to dielectric constant (dk) and ability to withstand heat (Tg):

Circuit board material comparison
Circuit board material comparison

The above table does not list all possible combinations of circuit board materials. However, it does provide circuit board materials that can be used for standard and special PCB board types and can, therefore, help you make the best selection for your design. As previously mentioned, there are additional circuit board properties that you should include in an overall evaluation of a PCB material. This evaluation should be done in conjunction with your CM to ensure that your design requirements align with your CM’s capabilities.