FPCWAY

Application of flexible printed circuit board (FPCB) in personal computer motherboards

Focusing on mechanical performance_2_ Experimentation

2.Experimentation

2.1. FPCB material testing

Material testing was carried out on a ready-to-use FPCB, which was purchased from PCB Universe located in the United States. This FPCB had an overall thickness of 0.1 mm and is single-sided, consisting of single polyimide and single copper layers. As shown in Fig. 1, this test was conducted according to ASTM D638, which is  a standard test method for the tensile properties of plastics, using an INSTRON table-mounted Universal Testing Machine at a testing speed of 50 mm/min. From the test, the resultant stress–strain relationship of the material is shown in Fig. 2. The effective elastic modulus of FPCB was found to be 5.24 GPa in the linear elastic region, and its yield strength was estimated to be approximately 80 MPa.This effective modulus value was found to be close to that reported in a previous work.

2.2. test vehicle

Primarily, typical electronic components were removed from old  PC motherboards using a desoldering process. Only the identified  mechanically significant components were considered for analysis  in the present study because of the development difficulty; for  example, memory connector slots, PCI connector slots, I/O connectors, heat sink, and CPU fan. The less mechanically relevant components, such as capacitors, resistors, and integrated packages, were ignored in the current study. Each chosen compo- nent was individually attached onto the FPCB using strong adhesive, and  subsequently, the resulting FPCB motherboard was clamped vertically, as shown in Fig. 3. This prototype was believed to represent well a realistic motherboard mechanically.

2.3. Experimental setup

In the experiment, the test vehicle was tested in a wind tunnel, which had an adjustable fan speed, as shown in Fig. 4. For data measurement, the real-time flow-induced deflection of the FPCB motherboard was captured using a KEYENCE LK-G152 laser sensor  connected to a controller, which had an accuracy of 0.001mm.The position of the laser sensor can be easily manipu- lated using the  linked actuator. In addition, the captured  data were also displayed and stored in the computer for further anal-ysis. To measure the air  flow velocity, an anemometer with a probe, which had an accuracy of 0.01 m/s, was also incorporated in the setup. The experiment was conducted under few flow velocities by manipulating the fan speed  controller. At each velocity, the test was run a few times, and the  accompanying uncertainties were determined using the statistical t-distribution given by Eq.

where is the uncertainty value, tis the value that depends on the level of significance and degree of freedom, S is the standard devi- ation, and n is the number of tests. In the present study, by applying a 90% confidence interval, the t value was found to be 2.13.