How PCBs are manufactured ?
Like many of the PCBs Manufacturing Fabrication companies, QualTech Circuits uses Standard Industry Manufacturing Processes and Materials.
Once the order(s) received, Gerber data, Drill data, Fabrication drawing will be transferred to Engineering department for review. Engineering department will go through a checklist consisting of rules to make sure the design can be manufactured. Once that completes, tooling will be generated. Tooling consists of NC drill file, NC Rout file, Photo Plotting of the art work, Net List testing File, and a Job's Traveler.
At QualTech Circuits, we use many differences panel sizes from 9”X12”, 12”X16”, 12”X18”, 16”X18”, 16”X21” and 18”X24”. Depending on the quantities of parts ordered with the least number of step and repeat is tooled to fit that panel size. The smaller the panel size, the least time it takes to move and minimum tooling is required.
Once tooling has completed, the traveler is sent to production control to be logged in the computer and released to production to start manufacturing.
If it is a multi-layer board. The inner layers laminate are cut with the proper copper weight and cleaned before sending to the dry film department. Inner layers are coated with a dry film material so the imagine may transferred and developed. Inner layers are then sent to the Wet-Process department for etching to remove unwanted copper, leaving the board image. Quality Control inspects all panels to make sure that all processes are completed properly, and that traces and pads are within tolerances. Inner layers are placed in Black Oxide Tank, this process is to protect all inner layer copper through the heat of the lamination process.
Inner Layers are stacked in sequence with proper Prepregs in between the layers and with cooper foil on the outside to produce Multi-layer Panel. Depending on the type of the material, the lamination process can take from 90 minutes or longer at 350 degree F or higher. Once it pressed, these panels are treated as a double sided and ready for drilling. The panels are placed between Back-Up and Aluminum Entry material to ensure correct entry at time of drilling. It is pinned to the drilling table if it is double sided, or it is aligned by tooling holes if it is a multi-layers. It is drilled using the proper program and drill bits. This process varies depending on the size of the panel and the number of drill hits.
The next process is Electroless copper, which is copper deposited into the holes. Prior to the purchased of our Black Hole System, this process would take between 3-4 hours and to go through a number of chemicals to clean and to deposit copper into the holes wall. Since early 2001, QTCLI has purchased this Black-Hole System, this has helped us shorten the time to 45-60 minutes. In addition to the time savings it also decreased the use of water required.
Panels are coated with Duponts dry film material which is applied by putting the panels through hot roll laminator. Outer layers Images are transferred to the panels through a exposing process and then run through a developer. Then are being inspected by Q.C. before plating. At this time, only traces and areas that are to be conducted are exposed, the rest are covered with dry film.
Next is the Plating process, copper is to plated to the traces and hole walls. Panels are placed in plating racks and dip into the plating tanks. Depending on the amount of copper needed to plate the Amps and Time is set for the current to go through the panels to meet those needs. Normally one hour of plating time at 25AMPs per SQUARE foot is sufficient to achieve 1 oz of copper in the holes and on the surface.
After Plating, panels are then placed into a Stripping Tanks to remove all the dry film resist. The exposed copper (after dry film stripped) without plating is ready for etch off. The panels are then run through a Tin Stripper leaving only Copper over Circuitry (Bare Copper).
Q.C. will inspect the panels for cut traces, under etched, under strip before next process which is SolderMask. Liquid Photo Image (LPI) SolderMask is flooded onto the panels using a screen process. Panels are then tack dry in an oven with a low temperature for a short period of time before taking to dry film. Here, the SolderMask Images are transferred to the panels through exposing process. It then develops through LPI developer to remove all LPI on pads and holes; before it can be final cure, panels are inspected again for mask registration and or mask on the pads. It then is placed in a oven and baked for final cure at 350 degree for about 2 hours. Mask is then permanently on the panels.
Legend or Silk Screen is screened onto the panels using a screened stencil, with white Non Conductive Ink. This image of the legend is then transferred onto the panels with all information of components and their locations. Panels are again placed on a rack and put in to a oven for approximately 10 -15 minutes for curing of the legend.
Panels are then put through a Hot Air Solder Leveler (HASL). This process adds solder to the surface of pads and inside the holes for assembly.
CNC Routing process is the one of the last processes. Panels are aligned by tooling and pinned to stack of Back-Up material on the CNC table. Using the appropriate routing and, depending on the requirements, difference router bits to use to cut the boards to it final shape and dimensions. If the boards have connectors, they are beveled at this time along with any counter sinking or counter bore requirements
Electrical Testing of each individual board takes place using Bed of Nails (conventional) or Flying Probe Test (Fixtureless). Depending on the technology of the designs and or the quantity of the orders. With the cost of building the fixture and the time it involved, most of ProtoType and Small Production Order are tested on the Flying Probe Tester. Once boards are tested, a final inspection is performed on the final product before packing and shipping to our Customers.
Standard Gerber Data Modifications:
1) Inner Layers / Outer Layers:
a) Remove all I/L Non-Function Pad is preferred.
b) Minimum I/L Pad Annular Ring is Drill Diameter. + .014�, if Min A/R not meet, Tear- dropping will be processed. Ex: .030� drill diameter + .014� + .002� A/R = .046� pad.
c) Minimum O/L Pad Annular Ring is Drill Diameter. + .012�, if Min A/R not meet, Tear- dropping will be processed. Ex: .030� drill diameter + .012� + .002� A/R = .044� pad.
d) If the Thermal for Vias holes are too small or solid copper => use .005� dot pads.
e) PTH and NPTH are minimum .010� to Circuitry.
f) Copper to Board out line, Cut-outs, Chamfers, Countersinks are .010� Minimum.
g) All score lines must have clearance .020� per side from the center of score line.
h) Layers sequence indicators that extent past the board edge: use as is, do not delete.
i) Minimum of I/L plane Isolated(anti pad) is the finished drill size + .014� per side.
Ex: drill size is .030�, isolated pad .058�.
Ex: drill size is .012�, isolated pad .040�.
2) Solder Masks:
a) Minimum S/M clearance is .001� per side, .003� per side is preferred.
b) Minimum S/M clearance for NPTH is .003� per side, .005� is preferred.
c) Minimum S/M clearance for SMT is .001�, .003� is preferred.
d) Plugged via S/M is used the drill size plus .004�.
3) Silkscreens:
a) Minimum Silkscreen width is .006�. .008� is preferred.
b) Legend must be clipped from all SMTs and PTHs. Do not clips Customer�s LOGO.
c) Do not use via holes to clip Legend.
Note: All of the above modifications are standard. If customer specified �Do Not Modify the Gerber Data � in the Fabrication Drawing, must contact customer before process any of those modification. All of the above must be meet the minimum requirement. If any of the above is not meet the minimum requirement, contact the customer ASAP.