What is Gerber files?
Gerber files are a type of file format used to describe PCB designs. They contain the necessary data for a PCB manufacturer to produce a given design, including the copper layers, solder mask, component placement and silkscreen.
Gerber files are named after Gerber Scientific Instrument Company, which first developed the Gerber format. Gerber files are the standard for PCB design and can be imported by most CAD/CAM tools to allow for more complex editing and manufacturing of the board.
Gerber files are the most commonly used PCB files for PCB manufacturer. Engineers in PCB company read Gerber files to get the information needed such as copper trace pattern, drill size, PCB material, dimension, thickness, stack-up,surface finish etc, and then convert to production files which used in the production.
Three normally used formats for Gerber files
Gerber files usually has three formats as below:
RS-274-X (Gerber and aperture are combined together)
RS-274 (Gerber and aperture separated )
Introduction for layers in PCB files
In Gerbers, each layer are separated as a files. We can use CAM350 or any other software to import Gerbers. Usually, Gerber files has a standard .suffix which is helpful to recolonize the layers, for example a 6 layer PCB should contain the following files in the package:
- ↝Top Paste .GTP –top paste layer (for top layer solder stencil)
- ↝ Top Overlay .GTO –top silkscreen layer
- ↝Top Solder .GTS –top solder mask layer
- ↝Top Layer .GTL –top copper layer
- ↝MidLayer1 .G1 –inner layer 1
- ↝Internal Plane1 .GP1 –inner power plane layer 1 (negative)
- ↝MidLayer2 .G2 –inner layer 2
- ↝Internal Plane2 .GP2 –inner power plane layer 2 (negative)
- ↝Bottom Layer .GBL –bottom copper layer
- ↝Bottom Solder .GBS –bottom solder mask layer
- ↝Bottom Overlay.GBO –bottom silkscreen layer
- ↝Bottom Paste .GBP –bottom paste layer(for bottom layer solder stencil)
- ↝Mechanical1 .GM1–mechincal layer 1 (for inner slots)
- ↝Mechanical2 .GM2–mechincal layer 2 (for inner slots)
- ↝Keep Out Layer .GKO –outline of the PCB
- ↝Aperture Data.APR –aperture file
- ↝Drill Data .DRL –drill file
- ↝Drill Report.LDP– drill report
How are Gerber files used by PCB manufacturer
Gerber files are used by PCB manufacturer to produce PCBs. And engineers in PCB manufacturing company will read the Gerber files and fully understand the printed circuit boards before converting to production files.
Generally, the data in Gerber files are divided into two parts as picture below. One part is layout file (generally in the form of GERBER and NC Drill, and some simple flexible boards can also be in the form of CAD format file), the other part is the specification of PCB fabrication, which generally describes the material properties, board thickness, copper thickness (some multi-layer boards define lamination), solder mask&silkscreen color, surface treatment, and special process.
If the customer has no specification documents, and there are no fabrication instructions in the Gerber file, we should confirm the fabrication technique with the customer.
In the inspection of specific data, we need to grasp the main information first, so as to determine the difficulty of the board, and then determine the basic price and delivery of the board.
Information we get from Gerber files
We can get all enough information to produce a printed circuit board from a complete Gerber files package, such as base material type, stakup, copper trace and solder mask pattern, drill size and position, surface finish, panel and all other information needed.
1) Base material,include copper thick&board thick,, rigid PCB or flexible PCB, and then confirm its layers, Usually, these are also the two most important parts that affect PCB price, PCB material information are normally described just like photo below.
In this photo,we can see that this board must choose IS410 FR4 raw material or equivalent TG180 material,1oz on inner layer and 1.5oz on outer layer,and 0.063inch board thickness.
The normal raw material for PCB have FR4,PI,high Frequency,aluminum substrate and copper substrate.,etc.
In addition to raw material type, it must be mentioned that the TG value is another key parameter for FR4 material.
TG value determines the heat resistance, moisture resistance, chemical resistance, stability and other characteristics of printed boards.
The higher the TG value is, the better the temperature resistance function of the plate is. Especially in the lead-free tin spraying process, high TG is used more often.
TG values are generally divided into three types: low TG 135, medium TG 150, and high TG 170
If the customer does not specify it, it is necessary to find the specification of the PCB type for comparison.
Some customers do not know the TG value and attributes of PCB. Our factory can give reasonable suggestions according to the use scenario of the board.
However, the higher the TG value is, the higher the cost of PCB is, so don’t blindly ask for higher TG, just find the appropriate TG value of the product itself.
About high Frequency substrate, usually choose Panasonic and DuPont brand, Customers who design high-frequency boards are professional and know which type of materials to choose, our more consideration is the inventory and procurement cycle of material.
For Aluminum PCB, Aluminum substrate is composed of circuit layer (copper foil), insulation layer and metal base layer. Compared with traditional FR-4, aluminum substrate can minimize thermal resistance and make aluminum substrate have excellent thermal conductivity. Therefore, it is common in LED lighting products. The thermal conductivity of aluminum substrate pcb is 1.0, 1.5, 2.0, 3.0, 5.0, and the most used are 1.0 and 2.0 W/m.k, meanwhile,Different thermal conductivity parameters correspond to different prices of aluminum substrate materials.
4) Surface finish , normally, including HASL – Hot Air Solder Leveling, Lead Free HASL, ENIG- Electroless Nickle/Immersion Gold, ENEPIG-Electroless Nickel Electroless Palladium Immersion Gold,Immersion Silver , Immersion Tin, OSP – Organic Solderability Preservatives.
the thickness of tin thick in the HASL process and the thickness of gold are also to be paid attention to. If the thickness is not defined, it is normally implemented according to the IPC-A-class 2 standard. IPC-A-class 3 is a high standard for processing, and needs to be clearly explained by the customer. We can only judge whether the class 3 standard is based on individual parameter requirements.
Among them, special attention should be paid to the requirements of gold fingers, electroplating of thick gold, and related beveled edges and requirements, normal 10-30u” gold plating for gold finger area. (notes,some pad arranged like fingers, which is used to insert into the card slot and is in contact with the metal spring plate in the card slot. Because this kind of design has high requirements on the wear resistance and electrical conductivity of the pad surface, a layer of nickel and a layer of gold will be plated on the pad surface, so it is generally referred to as a gold finger),A row of pads and slots with finger shape like the following is a typical gold finger board.
The priority is to pay attention to the type of HDI, which belongs to several levels of HDI, and then check the thickness and requirements of the dielectric layer in the laminate. If there is a specified thickness requirement of the dielectric layer, it is usually necessary to communicate with the customer to meet the actual blind hole processing requirements, and also pay attention to whether the blind hole is on the SMT pad. If there is, it is usually necessary to do VIPPO, which has met the customer’s SMT requirements.
The difficulty of rigid-flexible boards is processing and manufacturing, especially the control of yield. The following picture is the classic rigid-flexible board data. The relatively narrow area is the flexible part, and the other is the rigid area. Of course, the details should be based on the data.
he requirement for copper is relatively thick. Generally, 3OZ-6OZ is thick copper plate, which tests the etching control ability of the factory.
Vias in pad VIPPO Via in Pad Plated over technique,VIPPO is also used to ensure the welding ability of SMT pads, especially BGA pads.
The carbon oil board is mostly used for key boards, making full use of the conductivity of carbon oil. After heating and curing, the ink film is not easy to oxidize, and the performance is stable.,etc. The following picture is the classic key board with carbon oil technique for reference.
There are also some unusual technique related to holes ,such as Countersink holes, Press fit hole
In the solder resist part Layout checking is the last partwe will generally check the solder mask bridge problem, check whether the solder mask opening is matched with the corresponding pad, and pay special attention to the problems such as missing solder mask opening or exposure of the line and base material, if our engineer can’t make sure how to do, normally make EQ confirmation with the customer.
In the silkscreen part, it is mainly to check whether silkscreen characters are on pads ,whether the part number and version number on silkscreen layer are consistent with the product model, and often encounter that the original silkscreen frame is beyond the outline of board,in this case, we should consider the problem of Panel and SMT assembly.
The drilling part, mainly checks the size of holes, the spacing between holes, the spacing between holes and pads, and whether the Vias are on SMT pads, etc
For the panel part, In addition to the reasonable utilization rate of plates and the convenience of PCB processing, the convenience of SMT mounting and processing should also be considered. if there are component beyond the board, it is usually necessary to add frame or adjust the panel spacing and the panel direction to facilitate SMT processing.
The following 4UP is the panel we adjusted according to this situation, that is, we need to reverse single piece, and increase the piece spacing and breakaway tabs to meet the actual SMT manufacturing requirements.
The following is the picture of a single finished product after SMT.