How to ensure the quality of HDI PCB circuit boards

How to ensure the quality of HDI PCB circuit boards

In order to ensure the production quality of HDI circuit boards, manufacturers have undergone various testing methods during the production process, each of which will target different defects of HDI circuit boards.

1. Solderability testing of HDI circuit boards

The focus of solderability testing for HDI circuit boards is on the testing of solder pads and plated through holes. Standards such as IPC-S-804 specify the solderability testing methods for HDI circuit boards, which include edge immersion testing, spin immersion testing, peak immersion testing, and solder bead testing.

2. Internal defect detection of HDI circuit board

Microscopic sectioning technology is generally used to detect internal defects in HDI circuit boards, and its specific detection methods are clearly specified in relevant standards such as IPC-TM-650. The main testing items for microscopic section inspection include the thickness of copper and tin lead alloy coatings, alignment between internal conductor layers of PCB multi-layer circuit boards, laminated gaps, and copper cracks.

3. HDI circuit board size and appearance inspection

The content of HDI circuit board size detection mainly includes the direct processing of holes, spacing and tolerance, HDI circuit board edge size, etc. The content of appearance defect detection mainly includes: alignment of solder mask and solder pad; Whether there are impurities, peeling, wrinkling and other abnormal conditions in the solder mask; Whether the benchmark mark is qualified; Whether the width (line width) and spacing of circuit conductors meet the requirements; Whether the multi-layer board is peeled off, etc. In practical applications, HDI circuit board appearance testing equipment is often used for inspection. Typical equipment mainly consists of computers, automatic workbenches, image processing systems, and other components. This system can detect the inner and outer layers of multi-layer boards, single/double-sided boards, and base film; Can detect broken wires, grounding wires, scratches, pinholes, line width and spacing, rough edges, and large area defects.

4. HDI circuit board solder mask integrity test

Dry film solder mask and optical imaging solder mask are generally used on HDI circuit boards, which have high resolution and non flowability. Dry film solder mask is pressed onto a PCB under pressure and heat, requiring a clean HDI circuit board surface and effective lamination process. The surface viscosity of this solder mask tin lead alloy is poor, and under the thermal stress impact generated by reflow soldering, peeling and fracture phenomena often occur from the surface of HDI circuit boards. This type of solder mask is also relatively brittle, and may produce microcracks due to the influence of heat and mechanical forces during leveling. In addition, physical and chemical damage may also occur under the action of cleaning agents. In order to identify potential defects such as dry film solder mask, strict thermal stress tests should be conducted on HDI circuit boards during incoming inspection. When the peeling phenomenon of the solder mask cannot be observed during the experiment, the HDI circuit board specimen can be immersed in water after the experiment, and the peeling phenomenon of the solder mask can be observed using the capillary action of water between the solder mask and the PCB surface. HDI circuit board specimens can also be immersed in SMA cleaning agent after testing to observe whether they have physical and chemical interactions with solvents.