Classification of SMT reflow welding problems

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The last step in the SMT section's manufacturing of a fr4 PCB is reflow soldering. Lack of tin, short circuit, side standing, offset, missing parts, many parts, incorrect parts, reversal, monument, crack, tin bead, poor soldering, hole, and glossiness are some of its printing and mounting flaws. After welding, its neutral monument, fracture, tin bead, poor soldering, hole, and glossiness are distinctive flaws.

Monument: the occurrence of a component's one end leaving the pad and rising vertically or slanted.

There can be a solder connection or short circuit between two or more disconnected solder joints, or the solder in a solder joint may not be linked to the wire next to it.

Departure/displacement: The component departs from the intended location in either the pad's rotational (vertical), horizontal, or longitudinal directions.

Empty welding occurs when a component's solderable end is separated from the bonding pad.

Reverse direction: When the polarity element is inserted, it is oriented incorrectly.

Parts that are incorrect: The components attached at the designated position do not meet the required model or specification.

Fewer parts: materials are not glued where necessary components are needed.

Exposed copper occurs when the green oil covering the PCBA wears out or is damaged, exposing the copper foil.

Blistering: There is a localized expansion deformation on the PCBA/FR-4 PCB surface.

Tin hole: The component solder junctions have blowholes and pinholes after going through the furnace.

Crack in tin: surface crack in tin.

Hole plugging: the solder paste stays in the screw or plug hole, as well as in other guide holes.

Foot warping: The multi-pin component's foot is twisted and distorted.

Side standing: the welding end of the component is directly welded to its side.

fake welding or fake welding refers to the connecting and disconnecting of components that are not welded firmly and have inadequate contact as a result of internal or external stress.

Back/back: The product name and specification screen printing font cannot be recognized, and the component list is pasted by screen printing on the opposite side of the fr4 pcb.

Cold welding, also known as non-melting tin, requires that the crystal be fully melted in order to produce a consistent welding result, and the solder junction surface must not be glossy.

Classification of SMT reflow welding problems

SMT Stencil, a unique mold designed for SMT manufacturing, is another name for steel mesh. Its primary job is to assist with solder paste deposit; the goal is to precisely transfer the solder paste to the empty fr4 pcb's appropriate place. Since SMT technology has advanced, SMT steel mesh has also been extensively utilized in rubber processes like red glue.

1. Model of chemical etching

Chemical etching creates the template opening, which can be used to create brass and stainless steel templates with the following features:

1) The solder paste's poor releasing performance and bowl-shaped aperture;

2) It is limited to printing parts having PITCH values of 25–50 mil, or more than 20 mil;

3) The formwork is between 0.1 and 0.5 mm thick;

4) The opening's size error (position error) is 1 mil;

5) The cost is less than that of electroforming and laser cutting.

2. Laser cutting template

Laser cutting is used for the last opening, which has the following characteristics:

1) The upper and lower openings are naturally trapezoidal, and the upper opening is usually 1~5mil larger than the lower opening, which is conducive to the release of solder paste;

2) The hole size error is 0.3~0.5mil, and the positioning accuracy is less than 0.12mil;

3) The price is more expensive than chemical etching and cheaper than electroforming;

4) The hole wall is not as smooth as the electroforming formwork;

5) The thickness of u5kemanzu formwork is 0.12-0.3mm;

6) Usually used for printing in fr4 pcb when the PITCH value of the component is 20mil or less.

Why Choose China PCBA Supplier KSPCBA as Your Classification of SMT reflow welding problems Manufacturer?

– Experienced and skilled team

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