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PCB/PCBA knowledge
Four PCBA inspection items you need to know

PCBA inspection is an essential part during PCB manufacturing and assembling. How many classifications of PCBA inspection items are there? According to IPC and China’s military standards, inspection items are divided into four categories that are material inspection, process inspection, identification inspection, and quality consistency inspection.

Table of Contents

Material inspection

Material inspection in the SMD electronics manufacturer is an important part of the quality control of the PCBA board production process. It is also a part of the quality assurance for customers. All this can proves that the materials used in the PCBA board are qualified after re-inspection procedure.

When our customers would like to check the material of the finished PCBA board, the material inspection can be used as a proof that the material quality conforms to the design document or order contract.

The material inspection shall be composed of the original product qualification certificate of the material SMT factory and the identification data obtained by the PCBA board manufacturer through counting and sampling according to regulations.

Retesting must be performed on critical materials suitable for use in printed board production, including substrates, prepregs, and other process materials.

The re-inspection should be aimed at the main parameters that have an impact on the product. Process materials usually check the material’s qualification certificate and conduct necessary process tests to determine the quality of the material. It is not necessary to test or inspect all the properties of the material. Because it is impossible and unnecessary for any professional SMT processing factory to have the test conditions and capabilities for all materials.

Process inspection

Process inspection
Process inspection

The process inspection of SMT processing enterprises is the quality inspection in the PCBA board production process. It is the basis for ensuring the quality of the final product and an important part of the quality assurance system. The SMT patch foundry should set up appropriate inspection points according to its own production quality stability, process characteristics and product quality level requirements.

The combination of self-inspection, mutual inspection and special inspection is the most beneficial. It is difficult to achieve a three-level inspection system in mass production, but at least there should be self-inspection and special inspection.

The inspection points should be set at least after the photolithography plate, hole metallization (plated hole integrity), inner and outer conductive pattern etching (inspection of line width and spacing level pattern defects), before coating of solder mask (inspection of cleanliness), after drilling and shape processing, and before circuit switching and product packaging. The inspection records should be taken.

During the production process, the equipment, key solution and plating solution should be checked regularly or irregularly, and the operation status of the equipment should be checked at any time for the automation equipment.

Also read: PCB VS PCBA – What’s the difference

Identification test

The identification inspection is used to prove that the PCBA board manufacturer has the ability to produce the products specified in the standard. It is also the certification inspection of the production capacity and the identification of new products for the customers to select a qualified PCB supplier.

The inspection should be carried out in the inspection of PCBA boards produced with the equipment and process used in normal production. The qualification inspection must meet all the requirements of the specified product level. 

The identification inspection can use standard test samples, finished boards, trial production samples, or past performance data that can be evaluated as equivalent values by both the supplier and the purchaser (generally, group B inspection items with relatively high test costs). The size of the test sample should be in accordance with the relevant regulations or the national standard GB2828 or agreed upon by both parties.

SMT processing plant quality consistency inspection

SMT processing plant quality consistency inspection
SMT processing plant quality consistency inspection

The quality consistency inspection is carried out on the finished PCBA board or the quality consistency attached board to ensure the inspection of the delivered product quality. When the attached board is used, it shall be manufactured according to the graphics specified in the standard and its position on the jigsaw board.

For each attached board with consistent quality and its corresponding finished board, there shall be proof that they are on the same board in process traceability flags. Quality consistency inspection should include group A inspection (batch by batch inspection) and group B inspection (period inspection).

(1)Group A inspection of SMT proofing shall be inspected batch by batch, and all products delivered to users shall be inspected by Group A. For different levels of products, the inspection items and frequency are different. Here the table for the inspection items of group A of each level of board.

Product level

Inspection items

Level 1

Visual inspection items, dimensions, warpage, coating adhesion, electrical, circuit continuity and short circuit

Level 2

Visual inspection items, dimensions, coating adhesion, warpage, plating hole integrity, additional dimensional requirements, circuit continuity and short circuit, moisture (2 times per month)

Level 3

Visual inspection items, dimensions, weldability, bonding strength of non-supported holes (as required), solder resistance film curing and adhesion, coating adhesion, integrity of plated holes, warpage, additional dimensions, thermal stress (float welding) test, insulation resistance, circuit continuity and short circuit, cleanliness (2 times per lot)

The products that have passed the group A inspection shall not be postponed for delivery before the end of the group B inspection. Because group B inspection is carried out periodically, as long as group A inspection is qualified, it should be delivered.

(2)Group B inspection is carried out according to the specified cycle, and the items and frequency of inspection for different levels of products are also different. Here the table for the inspection items of group B of each level of board.

Product level

Inspection items

Level 1

Plating hole integrity, additional dimensions, weldability, thermal shock (float welding) test, insulation resistance, solvent resistance

Level 2

Weldability, solder resistance film curing and adhesion, thermal shock (float welding), voltage resistance, insulation resistance, cleanliness and solvent resistance

Level 3

Analog rework, voltage resistance, solvent resistance, moisture absorption, temperature shock, insulation resistance after wet heat, environmental adaptability (as per contract)

For the above inspection items, if the material or process changes, SMT manufacturers should conduct experiments at any time to determine the impact of material and process changes on the quality of PCBA boards.

If Group B inspection fails, for 3 levels product boards, the supplier shall notify the user units that have shipped during Group B inspection to suspend product acceptance until the PCBA board supplier takes corrective measures and re-performs B inspection. If the repeated inspection is still unqualified, the supplier shall inform the user of the unqualified information and the corrective measures to be taken.

The frequency and period of inspection shall be in accordance with relevant standards or contract provisions. The sampling method and test method for inspection should refer to relevant standards, and will not be described in detail here.

  • Visual inspection
  • AOI detection
  • X-ray inspection

PCBA testing can uncover a variety of defects, including incorrect components, faulty solder joints, problems with assembly, components that are missing or improperly mounted bad wiring connections, and corrosion.

In order to ensure that the final product has a high degree of quality, one of the procedures that must be completed is testing and inspection of the PCBA. After the PCB assembly has been completed, it will undergo testing to ensure that it functions properly. 

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