Keyword: PCB substrate, process of PCB
General technological process of PCB including: cutting, drilling, heavy copper - graphic transfer - graphic plating, etching, resistance welding - character - surface treatment - bei gong, final inspection, packaging for shipment. Cutting and drilling is easy to understand for most PCB fans, so this paper about the sink copper is! In printed circuit board manufacturing technology, this process is a process with the key. If the process parameters control is bad will create empty hole wall, and many other functional problems.
A. The purpose of heavy copper and function:
In the drilling of non-conductive hole on the wall of the base material, use the method of chemical deposition on a thin layer of chemical copper, as the electroplating of copper base;
B. Process:
burring → Alkaline degreasing → Secondary or tertiary countercurrent rinsing→Coarsening (micro erosion) → The secondary countercurrent rinsing → preimpregnation → excitation → The secondary countercurrent rinsing → peptize → The secondary countercurrent rinsing → electroless plating copper → The secondary countercurrent rinsing → pickle
C. Process description:
(a) deburring:
On purpose: before sink copper PCB substrate through the drilling process, this process are most likely to produce burr, it is the most important of inferior hole metallization. Deburring process method must be used to solve. Usually adopts mechanical method, and the inner hole on the side of hole wall without barb or blocking phenomenon.
(b) the alkaline degreasing:
Functions and purposes: to remove surface oil pollution, fingerprints, oxides, dust hole; Polarity of hole wall base material carried out (make hole wall changed from negative to positive charge) to process after adsorption of colloid palladium; More for alkaline degreasing, acid system, but the acidic degreasing system more alkaline degreasing system regardless of the oil removal effect, or charge adjustment effect is poor, all that is in the production of the heavy copper backlit effect is poor, binding force of hole wall is poor, board face oil removal is not net, prone to peeling foaming phenomenon.
Alkaline system compared with acidic degreasing degreasing: operating temperature is higher, cleaning is difficult; Therefore when using alkaline degreasing, more strict with oil removal after cleaning Good or bad will directly affect the oil removal adjustment sink copper backlit effect
(c) the micro erosion:
Functions and purposes: removal of surface oxide, coarsening panel, ensure that subsequent sink copper layer and good bonding force between the bottom of the base material copper; The activity of the new generation of copper surface has a strong, can very good adsorption colloid palladium
Coarsening agent: with coarsening of the agent on the market at present with two major categories: sulfuric acid hydrogen peroxide system and a sulfuric acid system and acid peroxide system advantages: large amount of dissolved copper, (up to 50 g/L), water and sewage treatment is easy, low cost, can be recycled, disadvantages: uneven surface coarsening, poor bath stability, easy decomposition of hydrogen peroxide, heavy air pollution including sodium persulfate and persulfate ammonium persulfate and ammonium persulfate sodium persulfate relatively expensive, water sex is a bit poor, sewage disposal is more difficult, compared with sulfuric acid hydrogen peroxide system, persulfate has the following advantages: good bath stability, uniform surface coarsening, disadvantages: soluble copper small amount (25 g/L) in the persulfate system copper sulfate crystallization precipitation, water sex is a bit poor, high cost; Another new inhibitor ChanGuo potassium hydrogen sulfate, dupont, bath stability, uniform surface coarsening, coarsening rate stability, not affected by the influence of copper content, simple operation, suitable for fine lines, small spacing, high frequency board, etc
(d) presoak/activation:
Presoak purpose and function: mainly to protect palladium slot from pre-treatment bath pollution, prolong the service life of palladium trough, the main ingredient in addition to the palladium chloride agree with palladium bath composition, wet hole wall, which can effectively facilitate the subsequent activation fluid into the hole in time activation enough useful activation; Presoak liquid proportion generally remain at around 18 baume degree, this palladium bath can be maintained in the normal proportion of 20 baume degree above
Activation and function: the purpose of the pretreatment of alkaline degreasing polarity, positively charged hole wall can effective adsorption of negatively charged colloid palladium particles, enough to ensure the uniformity of subsequent sink copper, continuity and compactness. So the quality of the oil removal and activation of subsequent sink copper plays a very important role, Production should pay special attention to the activation effect, mainly is to guarantee enough time, concentration of (or intensity) Activation of palladium chloride liquid exists in the form of colloid, the negatively charged colloid particles determines the palladium bath maintenance: point out the key to ensure a sufficient number of stannous ions and chloride ions to prevent colloid palladium glue solution, (and maintain adequate proportion, usually in 18 baume degree above) enough acidity (the amount of hydrochloric acid) to prevent stannous generated precipitation, temperature shoulds not be too high, otherwise the colloid palladium precipitation, will happen at room temperature or below 35 degrees.
(e) glue solution:
Functions and purposes: can effectively remove the colloid palladium particles surrounded by stannous ions outside, make palladium nuclear exposed in colloid particles, to start direct catalytic chemistry sink copper reaction,
Principle: because tin is sex element, it is soluble in acid and salt soluble in alkali, acid and alkali solution can do glue, therefore, but base on the water quality is relatively sensitive, easy to produce precipitation or suspended solids, easy to cause sink copper hole broken; Hydrochloric acid and sulphuric acid is a strong acid, unfavorable and multilayer board, not only because of the strong acid will attack the inner black oxide layer, and easy to cause excessive glue solution, the colloid palladium particles from hole wall board face turned down; More commonly used fluoboric acid as main glue solution, because of its weak acid, generally do not cause excessive glue solution, and the experiment proves that using fluoboric acid do glue solution, the adhesion strength of the copper layer and backlighting, density has increased significantly.
(f) heavy copper:
Functions and purposes: by palladium activation induced chemical sink copper autocatalytic reaction, the new generation of chemical copper and hydrogen reaction by-products can be as a catalyst for catalytic reaction, make sink copper reaction constant. Through this step after processing deposits a layer of chemical on the surface or hole wall copper.
Principle: the use of formaldehyde in alkaline conditions reducing to restore the complexation of soluble copper salt.
Air mixing: bath to maintain normal air mixing, the purpose is to bath the cuprous oxide ion and copper powder in bath, make it into soluble bivalent copper.
Source: //www.seekic.com
