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PCB Fabrication Methods Are Additive Method To Reduce The Two Categories
Sep 30, 2017

PCB Chinese name for the printed circuit board, also known as printed circuit boards, printed circuit boards, is an important electronic components, is the support of electronic components, electronic components is the electrical connection provider. Because it is made using electronic printing, it is called "printed" circuit board. PCB manufacturing methods are additive method, reduced into two categories.

Addition method: On a substrate that is not copper-clad, a conductive plate is selectively deposited to form a conductive pattern. Silk screen plating method, paste method and so on.

Decentralization: On a copper plate, a printed circuit board PCB is made by photochemical method, screen printing, or plating of a patterned resist layer, followed by etching out a non-patterned copper foil or mechanically removing unwanted portions. And reduced into the main method of carving and etching two. Engraving method is to use mechanical processing methods to remove unwanted copper foil, in a single trial or amateur conditions can be quickly printed printed circuit board PCB; etching method is to use chemical corrosion method minus the need for copper foil, which is currently The most important PCB manufacturing method. Here we mainly look at the etching method.

1. pattern plating etch process

(1) process to double-sided panel, for example, the process: cutting → drilling → PTH (electroless copper) → copper plating → optical imaging → graphics plating → alkaline etching → solder resistance + character → hot air leveling HAL) → Machining → Electrical Performance Test (ETest) → FQA → Finished Product.

(2) POINT Selective plating only for conductive patterns. Plate drilling, electroless copper plating, light imaging to form a conductive pattern, this time only the lines and holes and pads for copper plating, so that the average copper thickness of the hole is greater than or equal to 20μm, and then tin (tin plating as an etching resistance (Or wet film), alkaline etching, to get the desired wire pattern. Return the surface and the hole within the tin coating, screen printing resistance welding and character, hot air leveling, machining, electrical performance testing, get the required PCB.

(3) Features of the process more complex, but relatively reliable, can do fine lines. Europe and the United States, most Chinese companies use this process to produce.

2. panel plating etch process

(1) process cutting → drilling → PTH (electroless copper) → copper plating → light imaging → acid etching → solder resistance + character → hot air leveling (HAL) → shape processing → electrical test (E-Test ) → FQA → finished product.

(2) points

① plate drilling and electroless copper plating (PTH), the whole board and hole plating to the required copper thickness, so that the average copper thickness of the hole is greater than or equal to 20μm.

② only in the hole and graphics covered with dry film, dry film for the erosion layer.

③ in the acid etching solution to remove excess copper, so as to get the desired wire pattern.

(3) Features

① process than the graphic plating etching method is simple, but the process control will be more difficult. Many Japanese companies use this process, there are a small number of domestic enterprises with this method mass production

② Difficulty: the uniformity of the thickness of the copper layer on the board is more difficult to control. There are thick copper around the board, the middle of the thin phenomenon, etching is difficult to uniform, thin line difficult to produce.

③ dry film cover hole, especially the hole of large holes, such as concealment, etching into the hole, the hole copper is eroded, this board can only be scrapped.

3. SMOBC law

Cover the bare copper wire with solder resist and then hot air leveling, or Ni / Au, or Ag, or OSP (orgable solder protective prescription). (Pb-Sn, or metal layer N i / Au, Ag, Sn, OSP), only holes and pads are coated with lead tin (or N i / Au, Ag, Sn, OSP) ).

The role of this process is: to prevent the PCB in the assembly of welding caused by line bridging; saving metal costs; line resistance to the solder to get a good adhesion. If the line is lead - tin solder, welding line when the solder layer will be crisp.

SMOBC is actually a graphic electroplating etch method. This method has been used for twenty or thirty years. The 20th century, the seventies and eighties, in the bare copper line coated with solder, the hot air leveling, Guangdong people commonly known as spray tin. The solder is Pb-Sn solder, Pb: Sn is 37: 63 or 40: 60, this alloy has the lowest melting point of 183 ° C, Pb: Sn is 40:60 and the melting point is 190 ° C.

Hot air leveling (spray tin) process, the pad on the Pb-Sn is not smooth, resulting in surface mount SMT difficult, and pure gold solderability is excellent in the wire pattern, hole, pad all plated sickle / gold (Kam as the bottom), after etching, except for the hole and pad all coated with solder resist, leaving only the hole and pad for the N i / Au, instead of Pb-Sn, which is Guangdong and Hong Kong people called Water gold plate process. Gold layer is 24K pure gold, can be welded, very thin, only O. 05 ~ 0.10μm.

Need to nickel plating base, 2 ~ 5μm thick, and then gold plating. Gold plating in the gold content is not much, about Ig / L gold. It should be noted that this solderable thin gold with the printed circuit board on the gold-plated layer has a different nature, plug gold plating is hard gold, wear, can be plugged hundreds of times, requires a certain degree of hardness of the gold layer, gold slot The gold liquid contains trace amounts of cobalt (nickel, antimony) elements.

And because lead-tin alloy lead in the lead, according to the EU directive, in July 2006 prohibited lead. So SMOBC process surface coating into today's chemical immersion silver, Shen tin, Shen Ni / Au, OSP instead of Pb-Sn alloy. The eternal separation of these processes, these processes are ultimately belong to the graphics electroplating etching SMOBC process.