Dual access flexible circuit board refer to the flex circuit which can be accessed from both top and bottom side but only has one layer of conductor trace. There’re coverlay openings on both sides of flex circuit so that there’re solderable PAD on both top and bottom sides, that is similar with double sided FPC, but dual access flex circuit board has different stack up because of only one copper trace, so no plating process is need to make plated through hole (PTH) to connect between top and bottom side, and trace layout is much more simple. Base material is copper only and thickness is always 1OZ because rigidness of thinner copper (such as ½ OZ) will be too low to be useful, and thickness of coverlay always to be at least 1mil (25um Polyimide + 25um Adhesive), so total thickness will be 0.13mm which is the same like the most cheapest option of 1 layer FPC. That stack up is also similar like opposite Flex Flat Cable (FFC) which also has one trace layer but can be connected from both top and bottom, but coverlay opening can be anywhere on dual access FPC, comparing to FFC which can only be on both end edges (gold fingers). Here is stack up of dual access flex circuit: Application:
Vibration Motor for Mobile Phone
LCD Module for Mobile Phone
Dual access circuit advantages:
It can be connected to both side through copper, and do not need to make a through hole. If it is 2 layers FPC, you have to make a through hole to connect both sides.
The flexibility and bendability are better than 2L flexible circuit because of simpler stack up
Soldering PAD can be anywhere on both top and bottom side.
Dual access circuit disadvantages:
Complex production process: The production process is similar to 2 layers flex circuit, but it will be more difficult and complicate compared with 2 layers flex. And the manufacturability of dual access circuit board will be limited due to production technique.
Easy to wrinkle. Because only copper itself, which is too thin and too flexible to be keep flat during manufacturing process, so it will be easy to tear up. When it comes to hot laminating process, wrinkles and blister will be happened more frequently.
Only few components can be placed on, because the copper trace easy to be broken if there’re too many components.
In most of cases, we will transfer dual access FPC into 2 layers FPC which is simpler to be made and the cost is the same. Please contact Best Technology today for more information or any enquiry for dual access flexible circuit.