PDIEC/TR63017:2015 IECTR63017:2015IEC2015 - 5 - FLEXIBLEPRINTEDCIRCUITBOARDS (FPCBs) METHODOFCOMPENSATIONOFIMPEDANCEVARIATIONS 1 Scope This Technical Report specifies a compensation method of Cu linewidth according to impeadance reduction by using noise suppression materials (hereafter referred to as NSMs) for FPCBs. This Technical Report presents an optimum result for maintaining a designated performance of FPCBs by using NSMs. It also indicates a measuring method for an impedance variation of FPCBs using NSMs with the prevailing TDR (time domain reflectometry) method.This method is restictedto measuring onlythevariation of an impedance value in accordance withthe determines nor indicates the structureormaterial ofFPCBs. 2 Normativereferences The following documents,in whole or in part, are normatively referenced in this document and are indispensable for its application.For dated references, only the edition cited applies.For undated references, the latest edition of the referenced document (including any amendments)applies. IPC2141A DesignGuideforHigh-Speed ControlledImpedanceCircuitsBoards http:/www.ipc.org/ 3 Apparatus 3.1 Time domain reflectometry Time domain reflectometry (hereafter referred to as TDR) is utilized to identify the impedance data at the specific frequency range of FPCBs. 3.2 Blockdiagramforimpedancemeasuring Figure1givesoneexampleofaTDRsetup TDR mainframe / Control unit IPC-2141a-9-1 IEC Figure1-TDRtestsystem PDIEC/TR63017:2015 - 9 - IECTR63017:2015IEC2015 NOTE A guideline for TDR is provided in Annex A. 4 Test specimen 4.1 General FPCBs using NSMs should reduce the effect of electro-magnetic interference. However, the impedance variation of Cu circuit lines. A major factor of impedance variation using NSMs is due to the structure variation of FPCBs, as shown in Figure 2. Via hole NSMS T Cover layer Pl Coverlayer Pl Adhesive Adhesive G(Cu) G(Cu) G(Cu) s(Cu) G(Cu) s(Cu) PI PI GND (Cu) GND (Cu) Bare FPCB Shield FPCB IEC IEC Figure 2a -<Micro strip line structure without Figure2b-<Strip linestructure withNSMs> NSMs> NOTE A guideline for the theoretical background of impedance variation is provided in Annex B. Figure2-Twotypesof impedancestructureofFPcB 4.2 Structure Test specimens shall be designed by two structures,i.e.with and without using NsMs in one the two parts of one bare FPCB and one shield FPCB)for equitable estimation. This structure has the merit of uniformly measuring at once a bare and a shield FPCB under the same condition. One FPCB without using NSMs has a structure of a micro-strip line.This type is called bare FPCB. 3.AnotherFPCB using NSMs has a structure of a strip line.This type is called shield FPCB (see Figure 3). A Cu line is formed with a linear distance direction, because the variation of the shield effect is very weak for a curved line. Generally, the number of Cu patterns of the test specimen can be over the 5 (for example LW1 ~LW5) for verification of the characteristic impedance (Zo). But the number and width of the Cu line shall vary in accordance with the supplier's activity. PDIEC/TR63017:2015 IECTR63017:2015@IEC2015 Via hole LW1 LW2 BareFPCB LW3 LWn LW1 bp LW2 Shield FPCB LW3 LWn > 5 cm IEC Figure3-Schematicdiagramofatestspecimen Size, spacing and number of via holes for test specimens shall not be limited, but sufficiently represented.Especially, via holes offer an important role to contact the NsMs with the ground (hereafterreferred to as AABUS). The length of the test specimen shall be over5 cm inorder to obtain stablevalues from the measuring equipment.Each end of the test specimen should consist of SMA (subminiature A) connectors.For discernment of a Cu line-width, write each -number to the bare-end of the testspecimenneartheSMAconnector. The decision of width and thickness of a test specimen shall depend on to the pitch or the number of the Cu line or according to the requirements of the user. However, generally the structureof thetestcouponshall beAABUS. An impedance