FPCWAY

Application of magnetic pulse welding technique

for flexible printed circuit boards (FPCB) lap joints_2_Experimental setup

Experimental setup

The block diagram of the discharge system is shown in Fig. 3 which is consisted of a capacitor bank (C) and a spark gap switch (G) with a one layer E-shaped flat coil. For optimizing the weld quality,three capacitor banks with different energy storage capacity were used in present experimental setup. The capacitor banks (CB) descriptions were summarized in Table 1. The capacitor bank is connected to the gap-switch and one-turn coil by a low inductance transmission line.

3.1.  General outlines of apparatus

Fig. 4 shows the general outlines of the magnetic pulse welding apparatus. The coil was made by Cr–Cu alloy. The main discharge current pass through the middle part of coil and the width of this part was designed to be 2.5 mm and length of40 mm. The thickness of E-shaped coil was 2 mm and its inductance was measured about 0.039 μH. The thickness of Al driver was 0.3 mm with size of 50 mm × 50 mm. The skin depth for a typical discharge in this Al driver sheet was calculated by Eq. (2) and it was about 0.22 mm. This value is enough to prevent of melting of FPCB and apply big electromagnetic force to Al driver sheet for rapid collision with FPCB and producing a solid state boding.

3.2.  FPCB sample

A typical FPCB samples and its dimensional size which were used in present experiment are shown in Fig. 5a. Three types of FPCB sheet (W1, W5 and W10) which almost is used in industrial applications was chosen in present experiment. The size of FPCB sheet is 40 mm ×40 mm and the width of copper rows are 1 mm, 5 mm and 10 mm for W1, W5 and W10, respectively. The cross sec- tion view of all FPCB sheet layers are same and are shown in Fig. 5b. The total thickness ofFPCB is about 110 μm and the polyimide film layer cover only 30 mm of copper foil and 10 mm of that is uncoated (welding zone).