Keywords: Rigid Flex PCB, Rigid Flexible PCB Manufacturer

A considerable surge has been seen in the prevalence of flexible printed circuit boards and Rigid Flex PCB technology in recent years. This is due to its advantages in the growing wearable electronics industry

Space savings and reduced weight are offered by Flex and rigid-flex PCB technology. With rigid-flex technology, small lightweight consumer electronics are often built today. However, in successful rigid-flex PCB design, there can be many challenges. In connecting electronic components in various non-consumer and consumer devices, both flexible and rigid-flexible printed circuit boards (PCBs) play a major role. As per the name, a rigid PCB is nothing but a circuit board built on a layer of a rigid base that is unable to bend. On a flexible base capable of folding, twisting, and bending, a flexible PCB otherwise known as a flex circuit is built. For decent thermal resistance and components, great support is offered by a rigid circuit board.

The primary progress trend of newly-developed electronics products involves high reliability, 3D assembly, and miniaturization as per the modern electronics products’ development trend. In terms of scale and technology, worldwide PCBs upgrade constantly. This is due to the expansion of the electronics market. Thereafter, for exploring numerous technologies compatible with the trend of development mentioned above, printed circuit board manufacturers have been striving. Flexible PCB design comes into being because of the limitations on applications and the environment. Thus, flex-rigid PCB was born to further ensure the 3D assembly ability and soldering capability of electronics products.

Rigid-flex PCB’s Fabrication technology maintains constantly increasing advancement of products and upgrading with technology development. Window fabrication is regarded as a core as far as key fabrication technology of flex-rigid PCB is concerned. including methods of resistance adhesive, laser cutting, copper foil etching, window opening, negative as well as positive depth control and filling method, leading window fabrication technologies of flex-rigid PCB is explained in this article.

Window Opening Method of Rigid Flex PCB

The process in which advantage of mechanical milling or mold punching is taken by rigid-flex PCB from Rigid Flexible PCB Manufacturer with a core board structure for eliminating rigid core in no-flow prepreg and a flexible portion is Window opening method. This is to facilitate the generation of flex-rigid PCB through lamination.

Cover Layer Coating

After overall and local coating, X-section analysis is implemented on through blind via. Thus, it is concluded that delamination issues can be defeated by the local coating technology due to the failure of electrical conductivity and thermal effect so that the reliability of the product will be enhanced.

PE Punching for Flexible Portion

After manufacturing the cover layer, PE punching should be executed as modifications will take place on flexible board size during lamination of the cover layer to enhance layer alignment.

No-Flow PP Window Manufacturing

In terms of various piece counts and different manufacturers, no-flow PP adhesive overflow amount can be tested with practical lamination process considered and based on IPC-TM-650 test principles. Flatness can be ensured at the interface of flex-rigid PCB after compensation design is carried out on the original customer’s window.

Window Manufacturing at Rigid Portion

For eliminating rigid core compatible with flexible portion, mold punching or mechanical milling should be used. While mechanical works on milling on low or mid-volume production, Mold punching works better on mass-volume production.

Copper Foil Etching Method of Rigid Flex PCB

The process in which the advantage of solutions is taken by rigid-flex PCB with a copper foil structure is Copper foil etching. In this process, the window at the flexible portion is exposed.

Lamination

During lamination, makes tensile stress is received by the external copper foil on PCB by the implementation of a special lamination layout structure. This occurs based on the different coefficients of thermal expansion meant for various materials. Thus, few issues like bad board surface flatness, copper foil damage as well as wrinkles, and bad PP adhesive filling can be defeated.

Window Etching

After electricity running with a copper-plated board is completed, Negative etching is carried out. With flexible board exposed, copper foil at flexible portion should be etched away.

Filling Method of Rigid Flex PCB

The process in which surface portion, as well as fillers, will be eliminated through blind milling and fillers are placed at the window of flex-rigid PCB is filling method.

Pre-stackup

Filler is placed into a hollow window during the process of stackup meeting the following requirement:

• Filler Thickness must be the same as that of filling
• Filler must be resistant to high temperature
• The filler must be smooth and soft on the surface
• Equal to the window with high stability, the filler Figure must be the same
• CTE must be lower than or equivalent to a substrate material

Molding

By applying mechanical milling, Window at the disconnected position at flex-rigid PCB is fabricated and mechanical depth controlled is used to fabricate the window at the connected position. The flexible area will be instantly exposed as filler is taken out.

Positive and Negative Depth Control Method of Rigid Flex PCB

The process in which a blind groove is manufactured in advance on the rigid board is the Positive and negative depth control method. The rigid board is adjacent to the flexible board. Combined with blind groove, the Mechanical depth control method is used during molding after laminating and stacking up. To make the flexible portion exposed, a rigid board will be then eliminated at the window position.

Blind Groove Fabrication for Rigid Flex PCB Board

The range from one-third or two-third of that of rigid core board is used to control the depth of rigid blind groove usually. To stop milling damaging flexible board, it must not exceed the range of practical mechanical depth control capability. In the following methods, a blind groove can be manufactured:

Blind groove by X-ray: To fabricate blind grooves in connected holes, a Carbon dioxide x-ray machine is used.

Mechanical milling blind groove:  By applying a digital-controlled milling machine, a Blind groove is manufactured.

V-cut blind groove: By applying a V-cut machine, a V-cut blind groove is manufactured.

Blind groove by laser cutting: by applying a UV laser cutting machine, the Blind groove is cut.

Key technologies of Rigid Flex PCB fabrication have been introduced by this article. For several types of rigid-flex PCB, window manufacturing and various methods work. To contribute to excellent performance and high reliability of flex-rigid PCB, all the methods can be applied cooperatively.