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Nowadays, design is increasingly pursuing miniaturization, low cost and high speed of products, especially in the mobile device market , which usually involves high-density  electronic circuits. Using Rigid-Flex Boards will be an excellent choice for the peripheral devices connected through IO.  Seven major advantages brought by the design requirements of integrating flexible board materials and rigid board materials in the manufacturing process, combining  the 2 substrate materials with prepreg, and then achieving interlayer electrical connection of conductors through through-holes or blind/buried vias are as below:

● Gold plating can be divided into thin gold and thick gold according to thickness. Generally, gold below 4u”(0.41um) is called thin gold, while gold above 4u” is called thick gold. ENIG can only make thin gold, not thick gold. Only gold plating  can make both thin and thick gold. The maximum thickness of thick gold on flexible board can be over 40u”. Thick gold is mainly used in working environments with bonding or wear resistance requirements.

● Gold plating can be divided into soft gold and hard gold by type. Soft gold is ordinary pure gold, while hard gold is cobalt containing gold.  It’s precisely because cobalt is added that the hardness of the gold layer greatly increases exceeding 150HV to meet the wear resistance requirements.

High Speed & High Frequency Material (Flexible)

	DK	Df	Material Type
FCCL (Polyimide)	3.0~3.3	0.006~0.009	Panasonic R‐775 series;Thinflex A series;Thinflex W series;Taiflex 2up series
FCCL (Polyimide)	2.8~3.0	0.003~0.007	Thinflex LK series;Taiflex 2FPK series
FCCL (LCP)	2.8~3.0	0.002	Thinflex LC series;Panasonic R‐705T se;Taiflex 2CPK series
Coverlay	3.3~3.6	0.01~0.018	Dupont FR series; Taiflex FGA series; Taiflex FHB series;Taiflex FHK series
Coverlay	2.8~3.0	0.003~0.006	Arisawa C23 series;Taiflex FXU series
Bonding Sheet	3.6~4.0	0.06	Taiflex BT series;Dupont FR series
Bonding Sheet	2.4~2.8	0.003~0.005	Arisawa A23F series;Taiflex BHF series

● Microstrip traces should have no vias, they must be probed from the trace side.

● Trace on the secondary side should be probed from the secondary side(The launch side should be on that side).

● The good design is that stripline traces should be probed from whichever side most reduces the via stub.

● The best results for stripline will be obtained by using short vias that are backdrilled.