Acceptance criteria for PCB Assembly

What is acceptance criteria for PCB assembly?

The acceptance criteria for PCB assembly are rigorous and ensure that the product is high quality.

Firstly, the components used in the assembly process must be compatible, which means they must have appropriate mechanical, electrical and thermal properties to work together in the circuit board.

Secondly, the components must be placed accurately on the board with the correct orientation. During placement, all pins should be soldered to the pads to ensure a good electrical connection and no shorts occur.

Thirdly, solder joints should have appropriate shapes and sizes to ensure reliable connections with minimal risk of failure over time.

Lastly, the overall board should be inspected to ensure that there are no defects and that it meets design requirements.

By abiding by these acceptance criteria, PCB assembly processes can ensure the highest levels of quality for the finished product. All of these criteria must be met for a successful PCB assembly.

All in all, PCB assembly processes need to meet the outlined acceptance criteria. And the most commonly used acceptance criteria for PCB assembly is IPC-A-610 standards for PCB and electronics assembly.

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What is IPC-A-610 standard

IPC-A-610, also known as the Acceptability of Electronic Assemblies, is the a widely recognized standard developed by the IPC (Association Connecting Electronics Industries). It is widely accepted as a complete reference for PCB assembly quality and an essential industry benchmark. It helps make sure that electronic assemblies satisfy the highest quality standards, offering customers confidence in their products’ performance.

IPC-A-610 generalizes the criteria for accepting or rejecting electronic assemblies and makes clear acceptable quality standards for electronic products. IPC-A-610 categorizes the acceptability criteria of IPC products into three major classes: Class 1, Class 2, and Class 3.

In Viasion, we only produce as IPC-A-610 Class 2 and Class 3.

What acceptance criteria for PCB assembly do we following in Viasion?

Here in Viasion, we following IPC-A-610 Class 2 or 3 standards to inspect all our PCB assmbly, to make sure our PCB assembly are produced as the highest industry standards. Besides, we will also inspect and delivery our products which meet customer’s special requirements, such as very strict visual standards, special package standards etc.

What are the main difference between IPC-A-610 class 2 and class 3

IPC-A-610 is the most widely used acceptance standard for printed circuit board assemblies. IPC-A-610 defines visual acceptability criteria for three classes of electronic products, Class1, 2, and 3. IPC-A-610 Class Class I is not commonly used any more. IPC-A-610 Class 2 and IPC-A-610 Class 3 are the two most common IPC-A-610 acceptance standards used in industry today. Therefore, it is essential to understand the differences between IPC-A-610 Classes 2 and 3 when deciding which standard to adopt for your product. IPC-A-610 demonstrates a practical and comprehensive set of acceptance criteria to ensure electronic products satisfy required quality standards. In addition, IPC-A-610 Classes 2 and 3 offer different levels of acceptability criteria. Thus, they are suitable for various applications.

Aspects	IPC-A-610 Class 2	IPC-A-610 Class 3
Reliability	Normal	High
Cost	Normal	High
Industry	Dedicated service electronics products, such as consumer electronics, laptops, communications, controls, lighting	higher reliability products such as automotive, medical, militarily, avionics, life support system
Inspection Standard	Lower standard solder joint acceptance, material finish, terminals, connections, mechanical integrity	High standard solder joint acceptance, material finish, terminals, connections, mechanical integrity

Keeping in mind the differences between IPC-A-610 Classes 2 and 3 is essential for successfully implementing IPC standards. Choosing between IPC-A-610 Classes 2 and 3 needs to take into account the type of application and desired levels of reliability, appearance, performance, etc.

Detailed illustration of our visual acceptance criteria for PCB assembly

Normally we following IPC-A-610 Class 2 and Class 3 to inspect our PCB assembly. Please refer to the illustrations below for a reference of the items we have checked.

Offset

The side offset (A) is less than or equal to 50% of the width of the solderable end of the component (W) or 50% of the pad width (P), which is determined by the one with smaller width.

The lateral offset (A) is greater than 50% of the width of the solderable end of the component (W) or 50% of the pad width (P), which is determined by the one with smaller width.

No end offset allowed.

Unacceptable: The side offset exceeds 50% of the one with smaller width. The solderable end of the cylinder exceeds the width of the component diameter or 25% of the pad width.

Unacceptable: The lateral offset exceeds 50% of the one with smaller width.

Unacceptable: The offset of the solderable end is outside the range of the pad.

Less tin, more tin at solder end

The width of the end solder joint (C) is at least 50% of the width of the solderable end of the component (W) or 50% of the width of the pad (P), which is determined by the one with smaller width.

The minimum solder joint height (F) is 25% of the solder thickness (G) plus the height of the solderable end (H) or 0.5 mm, which is determined by the smaller one between G and H.

The maximum height of the solder joint is the solder thickness plus the height of the solderable end of the component.

The picture below showing the defect: The width of the solder joint is less than 50% of the one with smaller width.

The picture below showing the defects: No solder joint creep height, insufficient solder, no wet solder joint on the vertical surface of the solderable end of the component.

The following picture shows the acceptable soldering situation: The maximum height of the solder joint (E) may extend beyond the pad or to the top of the metal plating of the end cap of the solderable end, but not to the top of the component body.

The side stand, turn over, and the warped end of components

The picture below showing the defects: The ratio of width (W) to height (H) is more than two to one; the component has less than 3 solderable end surfaces (metal cap ends).

The picture below showing the defect: The material side of the SMD component with exposed accumulation of electrical material is mounted on the board side of the PCB. That should be a process warning.

The picture below showing the defect: There is warping of the end of the SMD component.

The ratio of width to height does not exceed two to one (2:1). The surfaces of the solder pad and the solderable end of the component are completely 100% wetted and in overlapping contact. The component has 3 or more solderable ends with good wetting of the vertical surfaces.

The material side of the SMD component with no exposed accumulation of electrical material is mounted on the board side of the PCB.

Warping of the end of SMD components (It is called tomstoning).

The offset in castle-shaped components, the width and height of solderable end)

The maximum side offset (A) is 50% of the width (W) of the castle. No end offset.

The minimum width of the end solder joint (C) is equal to 50% of the width of the castle (W).

Normal wetting

The picture below showing the defect: The maximum side offset (A) is greater than 50% of the castle width (W).

The picture below showing the acceptable condition: The minimum width of the end solder joint (C) is less than 50% of the width of the castle (W).

The picture below showing the acceptable condition: The minimum solder joint height (F) is 25% of the solder thickness (G) (not shown in the picture) plus the castle height (H).

Flat, L-shaped and wing-shaped pins, lateral offset, the offset of the pin's toe

No side offset

The maximum side offset (A) is not greater than 50% of the pin width (W) or 0.5 millimeters [0.02 inches], which is determined by the smaller one of these values.

The offset of the pin’s toe does not violate minimum electrical clearance requirements.

The picture below showing the acceptable condition: The maximum side offset (A) is not greater than 50% of the pin width (W) or 0.5 millimeters [0.02 inches], which is determined by the smaller one of these values.

The picture below showing the defect: The maximum side offset (A) is greater than 50% of the pin width (W) or 0.5 millimeters [0.02 inches], which is determined by the smaller one of these values.

The picture below showing the defect: The offset of the pin’s toe violates minimum electrical clearance requirements.

Flat, L-shaped and wing-shaped pins, the minimum length and height of side solder joints

When the pin length (L) is less than 3 times the pin width (W), the minimum length of the side solder joint (D) is equal to 100% of (L).
When the pin length (L) is greater than 3 times the pin width (W), the minimum length of the side joint (D) is greater than or equal to 3 times the pin width (W) or 75% of the pin length (L), which is determined by the greater one between (L) and (W).

Solder joints on the heel extend beyond the pin thickness but do not fill to the bend on the pin.
There is no solder tin on the component body.

When the pin length (L) is greater than 3 times the pin width (W) and the minimum length of the side solder joint (D) is less than 3 times the pin width (W) or 75% of the pin length (L), which is determined by the greater one between (L) and (W).
When the pin length (L) is less than 3 times the pin width (W), the minimum length of the side solder joint (D) is less than 100% of (L).

The picture below showing the acceptable conditions: There is solder tin on the plastic component bodies, such as SOIC or SOT.
There is no solder tin on ceramic or metal component bodies.

The picture below showing the defects: There is solder tin on the plastic component bodies other than SOIC or SOT.
There is no solder tin on ceramic or metal component bodies.

Flat, L-shaped and wing-shaped pins, the minimum height of the solder joint on the heel, pin coplanarity

The height of the solder joint on the heel (F) is greater than the thickness of solder tin (G) plus pin thickness (T), but does not extend to the radius of the knee bend.

Components with neatly aligned pins (co-planar) to accept solder formation

The picture below showing the acceptable condition: The minimum height of the solder joint on the heel (F) is equal to 50% of the thickness of the solder tin (G) plus the pin thickness (T) at the connection.

The picture below showing the defect: The minimum height of the solder joint on the heel (F) is less than 50% of the thickness of the solder tin (G) plus the pin thickness (T) at the connection.

The picture below showing the defect: One or more pins of the component are misaligned and do not make proper contact with the pad.

Array arrangement of surface-mount surfaces, soldering

Target: BGA solder balls are placed in the center of the pad. There is no offset, continuous solder, false solder, and empty solder.

The picture below showing the defect: Bridging between solder joints detected by visual inspection or x-ray inspection.

The picture below showing the defect: The soldering is “waist-shaped”, indicating that the solder ball and solder paste do not flow together.

The picture below showing the defect: The reflow of solder paste on BGA solder balls is not complete. There is broken solder.

Soldering abnormalities：pinhole/blowhole, cold soldering, non-wetting

Target: Solder joints are wet. There are no pinholes/blowholes.

Target: Solder joints are wet.

The picture below showing the process warning defect: There are pinholes/blowholes.

The picture below showing the defect: There is incomplete reflow of solder paste.

The picture below showing the defect: Pins or pads to be soldered are not wet or semi-wet.

Soldering abnormalities: Solder balls / spatter, continuous tin, reticulated solder tin

Solder balls do not violate the minimum electrical gap.

Solder balls shall be fixed within the no-removal residue or covered under a conformal coating layer, adhering (soldering) to the metal surface.

Solder tin connects wires that should not be connected.

Solder tin forms a bridge between different wires or components that are adjacent to each other.

There is reticulated solder tin.

The picture below showing the defect: There is spatter of solder balls.

The picture below showing the defect: There is continuous tin.

The picture below showing the defect: There is reticulated solder tin.

Soldering abnormalities: Broken solder, disordered solder tin, burrs in solder tin

Normally we following IPC-A-610 Class 2 and Class 3 to inspect our PCB assembly. Please refer to the illustrations below for a reference of the items we have checked.

There is cracked soldering.

The soldering is moved due to the influence of external forces, and the solder joints show signs of disorder.

The picture below showing the defect: There is cracked solder tin.

The picture below showing the defect: The solder joints show signs of disorder.

The picture below showing the defect: The soldering violates the minimum electrical clearance.

Damages to components

Acceptable: Any edge spalling is less than 25% of the component width (W) or component thickness (T).

The missing of metal plating at the top of the end is up to 50% (each end).

There is no damage to the surface. There are no scratches, cracks, chips, or broken lines on the component body. Identity markings are clearly identifiable.

The picture below showing the defect: The missing of metal plating at the top of the end is more than 50% (each end).

The picture below showing the defect: The missing of metal plating at the top of the end is more than 50% .

The picture below showing the process warning: There is a depression or notch in the plastic component body that does not extend to the seal of the pin or expose the inner functional essence.

Cracks or other deformations affect the mechanical integrity or function of the enclosure.

The distance between the bend of the contact pin and the center is greater than 25% of the thickness/diameter of the contact pin.

Scorching or other damage affect the shape or other functions of the disk loading.

Chips or cracks expose the substrates of the component or functional materials or affect hermeticity, integrity, form, assembly, or function.

The dents and scratches of the component body affect the form, assembly and function or exceed the manufacturer’s specifications.

Damage area with signs of amplification, such as cracks, sharp angles, heat fragile materials, etc.

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