Surface mounting is a technology of manufacture of PCB-based electronic products, as well as related methods for design of printed board assemblies.
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The PCB surface mounting technology is also known as SMT and SMD technology, whereas components for surface mounting are also known as chip components. SMT is so far the most commonly used design and assembly method for PCB-based electronic units. The main difference between SMT and conventional technology, i.e. through-hole mounting, is that the components are mounted on surface of a PCB only at the side of wire tracks, which does not require any holes. Through-hole mounting and SMT can be combined in the same PCB. The SMT is advantageous by virtue of a combination of the component features, design methods and practices of manufacture of printed board assemblies.
The typical SMT process flow includes:
Individual hot-air or nitrogen soldering is also used for single-item production, equipment repair, and when mounting components requiring special precision, usually, during small-series production.
One of the critical process materials used for surface mounting is soldering paste (also sometimes known as solder paste). Soldering paste is a mix of powdered solder with organic fillers, including flux. Soldering paste is designed to:
During soldering, it is essential to ensure correct temperature change in time (thermal profile), in order to:
Thermal-profile development (thermal profiling) becomes now particularly important given expansion of lead-free technology. For lead-free technology, the process window, i.e. the difference between the minimum required and minimum permissible thermal profile temperatures, is noticeably narrower due to the higher solder melting temperature.
In terms of technology, surface mounting has the following advantages over the through-hole one:
In addition, the advantages above bring forth:
Chip components from 008004 and higher, microcircuits in any of the existing packages, including DIP, SOIC, PLCC, TQFP, PQFP, TSOP, HSOP, QFP, LCC, BGA, LGA, with the maximum dimensions of packages of at least 55x100 mm and weight of up to 100 g, flip chips, surface-mounted connectors, components mounted in holes.
Technical characteristics | |||
Parameter | Unit | Value | |
PCB dimensions (conveyor belt charging) | Min. | mm | 50х50 |
Max. | mm | 450х450 | |
Min. dimensions of the mounted component | Width | mm | 0,2 |
Length | mm | 0,1 | |
Max. dimensions of the mounted component | Width | mm | 55 |
Length | mm | 100 | |
Height | mm | 28 | |
Min. pin pitch for components | | mm | 0,1 |
Min. pin pitch for BGA components | | mm | 0,1 |
Min. pin diameter for BGA components | | mm | 0,04 |
Mounting speed for chip components | According to IPC 9850 | pcs/h | 10000 |
Positioning accuracy for components with small pin pitch, according to IPC 9850, at 3σ | X- and Y- deviation | mm | 0,025 |
Θ-deviation | ° | 0,06 |
Item No. | Activities (services) | Unit price, less VAT | Q-ty of items in a one-off batch, pcs |
1.1 | Mounting preproduction (for each mounting side) | 2 000,00 RUB | - |
1.2 | Screen making | from 7000,00 RUB | - |
1.3 | Making one (1) soldering point at the Surface Mounting Line (SML) for commercial products | 0,65 RUB | 90 – 150 |
The price is subject to VAT (20 %).
Note:
The item cost estimate formula is as follows:
Final price = q-ty of soldering points х 0.65 х K1 х K2 х K3 х K4 х K5 + cost of preparation activities + cost of screens
The factors used for the estimate are as follows: