4th Day - 10 July Tuesday

STANDARD OF SOLDERING

Where appropriate, the type of soldering process used has been addressed specifically in the criteria description. In any case, the connection criteria apply regardless of which methods of soldering have been utilized, for example:

• Soldering irons.

• Resistance soldering apparatus.

• Induction wave, or drag soldering.

• Reflow soldering.  

• Intrusive soldering.

The solder connection wetting angle (solder to component and solder to PCB termination) is not to exceed 90° (Figure 5-1 A, B). As an exception, the solder connection to a termination may exhibit a wetting angle exceeding 90° (Figure 5-1C, D) when it is created by the solder contour extending over the edge of the solderable termination area or solder resist.

 

Target - Class 1, 2, 3

•        Solder fillet appears generally smooth and exhibits good wetting of the solder to the parts being joined.

•        Outline of the lead is easily determined.

•        Solder at the part being joined creates a feathered edge.

•        Fillet is concave in shape.

Acceptable - Class 1, 2, 3

·      There are materials and processes, e.g., lead free alloys and slow cooling with large mass PCBs, that may produce dull matte, gray, or grainy appearing solders that are normal for the material or process involved. These solder connections are acceptable.

•     The solder connection wetting angle (solder to component and solder to PCB termination do not exceed 90° (Figure 5-1 A, B).

•   As an exception, the solder connection to a termination may exhibit a wetting angle exceeding 90° (Figure 5-1 C,D) when it is created by the solder contour extending over the edge of the solderable termination area or solder resist.

ELECTRONIC COMPONENT CATEGORY

SURFACE-MOUNT TECHNOLOGY (SMT)

Surface-mount technology (SMT) is a method for constructing electronic circuits in which the components are mounted directly onto the surface of printed circuit boards. An electronic device so made is called a surface-mount device (SMD). In the industry it has largely replaced the through-hole technology construction method of fitting components with wire leads into holes in the circuit board.


An SMT component is usually smaller than its through-hole counterpart because it has either smaller leads or no leads at all. It may have short pins or leads of various styles, flat contacts, a matrix of solder balls (BGAs), or terminations on the body of the component. There are several stages required to solder SMDs to boards. However there are two basic methods of soldering that are used. These two processes require the board to be laid out with slightly different PCB design rules, and they also require the SMT soldering process to be different. The two main methods for SMT soldering are Wave soldering and Reflow soldering.

THROUGH-HOLE TECHNOLOGY (THT)

Through Hole technology is a method for constructing electronic circuits in which the pin-through hole (PTH) components are inserted through holes drilled into printed circuit boards (PCBs). The ends, or leads, are then affixed to pads on the opposite side with molten metal solder using wave soldering or reflow soldering equipment. This process is also called through hole assembly. Through Hole technology replaced early electronics assembly techniques such as point-to-point construction. 

From the second generation of computers in the 1950s until surface-mount technology became popular in the late 1980s, every component on a typical PCB was a through hole component. While through hole mounting provides stronger mechanical bonds than surface-mount technology techniques, the additional drilling required makes the boards more expensive to produce. It also limits the available routing area for signal traces on multilayer boards since the holes must pass through all layers to the opposite side. For these reasons, through hole mounting is normally reserved for bulkier components such as electrolytic capacitors or semiconductors in large packages that require additional mounting strength to endure physical stress.