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Surface Mount Assembly Classifications for EMS

Aug 02, 2017

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Surface Mount Assembly Classifications

Three general classes for the intended end use of electronic assemblies have been established. As applications and functionality increase there may be overlap of equipment between classes. The owner of the application has the responsibility to determine the class that applies. Although a single class may be referenced, specific requirements defined in other classes may apply as well. If a class is not stated for a criterion then the single criterion applies to all classes.

Class 1: Consumer Products: This class of product includes non-critical applications which shall be reliable and cost effective but for which extended life is not the primary objective. Examples include products manufactured for general consumer applications.

Class 2 – General Industrial. This class includes high performance commercial and industrial products in which extended life if required but for which uninterrupted service is not critical. Application and environmental considerations should be taken into account.

Class 3 – High Reliability. Equipment in this class includes those equipment which continued performance is critical, equipment whose downtime cannot be tolerated, or equipment used as a life support item. Unless otherwise specified, Class 3 shall be used for soldering requirements on military electronic equipment.

Printed circuit assemblies are manufactured in a variety of ways, exclusively using smt devices or smt mixed with through-hole components. Boards which have both SMC’s and through-hole components are called mixed technology boards. Surface

mount components are conventionally attached to the substrate using the reflow or the wave soldering process. Typically PCBs are assembled in one of the following ways and categorized as:

Type 1:

SMC’s only are placed on one or both sides of a printed circuit board. The components are attached via the Reflow soldering process.

Type 2:

A combination of both surface mount and insertion mounted components on a printed circuit board. Both SMC’s and IMC’s are assembled on the top side of the board while SMC’s only are attached to the bottom of the board. Top side smt components are Reflow soldered, while the through hole and bottom side smt components are Wave soldered.

Type 3:

IMC’s are assembled on the top side of the board while SMC’s only are attached to the bottom of the board. The components are soldered in place via the Wave solder process.

The fast growth of these applications and advanced packages has led to the development of high density boards. As the industry increases the use of these boards and packages in its products, two of the greatest challenges that it will face are; establishing effective printing guidelines and utilizing equipment that can reliably produce a wide variety of assemblies.

A company’s success or failure in the surface mount industry will weigh heavily on its ability to adapt to automated manufacturing practices through innovative product design and development. Manufacturers can effectively compete in the electronics marketplace today only by utilizing automated equipment throughout the entire SMC assembly process. This includes addressing changes in the SMC production process from initial board printing to final inspection. The companies that do not act positively on these factors and successfully adapt to changing trends in the electronics market will find their business being lost to competitors and foreign ventures.

Type 1 – Single Sided SMT
SMT Components (Primary Side only)

Print Solder Paste Place SMT Components

Reflow Solder

Clean(if required) In Circuit Test/Rework

Surface Mount Process 1-13

Type 1 – Double Sided SMT
SMT Components (Primary & Secondary Side)

Print Solder Paste Place SMT Components

Reflow Solder

Clean(if required) Flip PCB

Print Solder Paste Place SMT Components

Reflow Solder

Clean(if required) In Circuit Test/Rework

Surface Mount Process 1-14

Type 2 – Mixed Technology
SMT &Through-Hole Components (Primary Side) Passive SMT Components (Secondary Side )

Surface Mount Process 1-15

Squeegee Aperture Paste

On Contact


Print Solder Paste Place SMT Components

Reflow Solder


Flip PCB

Place SMT Components

Cure Adhesive Flip PCB Wave Solder Clean (If Needed) Test / Repair

Insert / Clinch Through-Hole


Apply Adhesive (secondary Side)

Type 3 – Mixed Technology Through-Hole Components (Primary Side) Passive Surface Mount Components (Secondary Side )

Flip PCB

Place Surface Mount Components

Surface Mount Process 1-16

Insert / Clinch Through-Hole Components (Primary Side)

Apply Adhesive (Secondary Side)

Cure Adhesive Flip PCB Wave Solder Clean (If Needed) Test / Repair

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