As we all know, the burr will influence the product quality and looks not so beautiful, so today Iâll share you how we to decrease the burr when drilling.
First, the drilling bit must be new.
Usually, the drilling bit can be used for drilling 3000-5000 holes.
To avoid burr, we will change new drilling bit after drilling 2000 holes.
drilling holes
The drilling speed must be suitable.
Normally, the drilling speed is around 20W/drilling. The speed shouldnât be too fast or too slow. If too fast, it might cause holes burning.
Due to Flexible boards are suitable for more and more fields with their unique advantages of lightness, thinness and compactness. There are also many boards that need to be assembled components or various signal transmission, so the requirements for impedance are increasing.
Normally there are four factors will affect impedance. 1), DK Value. 2), copper thickness. 3), copper trace and space. 4), dielectric layer thickness (PI&coverlay). You can know more details from below picture.
Er1: DK value for base material, the DK value of different brands’ materials and thickness are not the same, the normal range is 3.15 to 4.2
T1: copper thickness, this is the finished copper thickness, itâs marked 30um in below table, thatâs means the base copper thickness will be around 18um.
W1: copper trace width, and S1 is copper trace space. Trace width and space are important for impedance.
H1: dielectric layer thickness, that is the PI thickness of the base material, PI thickness with adhesive thickness for adhesive materials.
W1&S1: copper width and space.
C1/C2/C3: coverlay thickness. 1/2mil coverlay is 28um, 1mil coverlay is 50um.
CEr: DK value for coverlay, 1/2mil coverlay is 2.45, 1mil coverlay is 3.4
Impedance diagram
Normally customers has required impedance value and total board thickness (stack up). So what can we do to meet the customer’s required impedance?
The first step, adjust copper trace and space to meet impedance, the smaller the trace width, the greater the impedance. Our minimum copper trace and space is 2mil, if we still can not meet impedance when copper trace adjusted to 2mil, then we have to move to second step.
The second step, normally the reference layer of impedance is copper foil, we can change the copper foil to grid copper, because the greater the grid spacing, the greater the impedance value.
The third step, if the above two steps still cannot meet the impedance requirement after adjustment, we need to communicate with the customer to adjust the stack up which included copper thickness, dielectric layer thickness and coverlay thickness.
Finally, we can calculate impedance and adjust copper traces for you if you need our service. If you would like to know more details, please contact us sales@bestfpc.com
