Never Underestimate PCB Half-Hole Boards
What is a PCB half-hole? Half vias are rows of holes drilled along the boundaries of a PCB for production purposes. When the holes are plated with copper, the edges are trimmed off so that the holes along the border are halved. The edges of the PCB look like a plated surface with copper inside the holes.
What is the purpose of half-holes? Modular PCBs are basically designed with half vias, mainly for ease of soldering, small module size and functional requirements. Usually, a half-hole is designed in the PCB single edge of the hole, in the gong shape gong half, leaving only half of the hole in the PCB, commonly known as a half-hole.
Design for manufacturability of half-hole plates
1. Minimum half-hole
Minimum half-hole process manufacturing capacity is 0.5mm, the premise is that the hole must be in the center of the profile line, which means that there must be 0.25mm holes in the plate. Otherwise, the copper of the hole wall will fall off during the production process, resulting in no copper hole, the finished product can not be used.
2. Half-hole spacing
The minimum finished aperture of the half-hole board is 0.5mm, and the aperture needs to be compensated in the manufacturing process after compensation of the half-hole and half-hole spacing needs to be ensured at ≥ 0.35mm, so the design of the half-hole spacing needs to be ≥ 0.45mm. Half-hole corresponding to the line pads after compensation to ensure that ≥ 0.25mm, half-hole corresponding to the soldermask window pads and pads must be made between the soldermask bridge.
3.Prevent assembly with tin short circuit
Designed for rectangular pins, half-hole aperture and pad width, etc., at this time some engineers may increase the width of the pad to ensure that the hole ring, ignoring the spacing of the pads in the assembly welding process leading to even tin short-circuit. In fact, a half-hole only needs to make the hole to the welding ring can be, without increasing the width of the entire pin, because half of the holes outside the board will be milled off when moulding.
4. Half-hole collage
The half-hole board layout should have a half-hole position with left spacing, making it easy to mold and mill the half-hole. In the PCB layout collage will ignore this point, because few layout engineers have been to the PCB factory to understand how the half-hole is made. For half-hole special products, often according to the normal boards without spacing collage V-CUT, resulting in half-hole copper by the V-CUT knife ripped off the hole caused by no copper, the product can not be used.
Semi-perforated plate manufacturing
1. Definition of half-hole plate
Half hole refers to the design of the metallization hole half in the board, half in the board outside, the product requires the hole wall of the copper skin to be retained device holes. Process flow: Drilling → copper immersion → board surface plating → outer layer of the line → graphic plating → lead tin plating → milling half-hole → desmear → etching → desmea
2.Half length slot processing
When the half-hole is a slot hole, it is necessary to add a ∮0.8-1.1mm guide hole at each end of the slot hole. The guide holes need to be put into the second drill layer separately to prevent the half-slot holes from uneven stress, copper skin warping, and in front of the milled half-hole to add a two-drill process.
3. Half-hole gong tape
The half-hole plate needs to be made into a closed frame with a width of 1.6mm, named GKO2 (milled half-hole before etching). Have set collage, need to do GKO2 (milled half-hole before etching) inside the SET, and the closed area can not enter the plate, this point is very important, in order to facilitate the shape of the drawing of the half-hole gong tape to facilitate the drawing of the gong tape to identify the half-hole area.
4. Half-hole connection
If the half-hole is delivered as a veneer and is surrounded by half-holes, each of the four corners of the bridge must be larger than 2mm to prevent the board from being interrupted in the production process. All around the half-hole SET, to add stamp holes in the corners of the board to connect, when the corners of the gong half-hole board connection is less than 1.6mm, no need to add stamp holes. Split boards can be broken directly.
5. Half-hole, Drilling line production
Half-hole board drilling and normal board drilling can be normal compensation. The minimum half-hole finished aperture is 0.5mm, the half-hole board shape is normal for copper cutting, and then normal stacked line pads, pad spacing ≥ 0.25mm, to prevent the finished product from welding even in a short circuit.
6. Half-hole solder resist production
Half-hole board closed area need to open the window, (if the half-hole board closed area does not open the window will lead to half-hole hole wall with ink into).
Half-hole corresponding to the line between the pads can not open the window, if you can not keep the bridge needs to be confirmed with the customer. It is recommended to change the distance between the half-hole, if you can not ensure that the pad spacing is easy to weld even tin.
The production process of half-hole plate is more complicated than ordinary plate, and the relative cost is also higher. If you do not use Huaqiu DFM to check in advance, it may lead to wrong calculation of the manufacturing cost of the product, and then realize the existence of half-hole in the product when manufacturing, which will delay the production cycle of the R&D product.
