I. Overview

black hole of the emergence of the traditional PTH is a challenge, its biggest feature is an alternative to traditional electroless copper process using physical role in the formation of the conductive film can be transferred directly to the plating . Analyzed from the viewpoint of efficiency, and its constituent processes simplify the procedure and reduce the controlling factor, as compared with the traditional PTH manufacturing process, reduce the number of use of drugs, the production cycle is greatly reduced, so the production efficiency is greatly improved, while sewage reduce the total cost of water treatment decrease, so that the printed circuit board manufacturing.

Direct plating of black hole characteristics

Black hole of the fluid does not contain the traditional electroless copper plating ingredients cancel formaldehyde and chemicals that endanger the ecological environment, such as EDTA, NTA, EDTP use in the recipe, belongs to environmental -type products.

2. Simplified process black holes process just 12 minutes, instead of the very thin and difficult to control the intermediate layer (chemical copper plating layer), thereby improving copper plating , adhesion, and improve the reliability of the PCB / FPC hole metallization.

3. Analysis, maintenance and management of the solution using the program greatly simplified.

4. Compared with traditional PTH, convenient operation, short production cycle, reduce waste disposal costs, thereby reducing the total cost of production.

5. Provide a new process - direct selective plating.

Black hole direct plating technology

3.1

It is a fine powder of graphite and carbon black conductive layer is formed, and then dip-coated on the wall of the hole to direct plating. Its key technology is the composition of the solution composition of the black hole. First, a fine and uniform dispersion of graphite and carbon black powder in the medium i.e. deionized water, and surfactant solution so that a uniform distribution of graphite and carbon black particles in the solution to maintain stability, but also has good wetting properties, so that graphite and carbon black can be sufficiently adsorbed on a non-conductor on the surface of the bore wall, the formation of a uniform and detailed, firmly bonded to the conductive layer.

3.2 components

Black holes solution mainly fine graphite and carbon black powder (particle diameter of 0.2-0.3μm), and the liquid dispersion medium is deionized water and a surface active agent composition.

3.3 various components of the role of

(1) graphite, and carbon black powder: it constitutes the main part of the solution of the black holes, play a role in conductivity.

(2) a liquid dispersing medium: is used for dispersing the powder of graphite and carbon black of high purity deionized water.

(3) a surface active agent: The main role is to enhance the stability of the suspension of graphite and carbon black and wetting properties.

(4): PH value :9.5-10.5, using temperature :25-32 degrees.

(5) :300-600c ㎡ / g.

3.4 black hole of the components of the solution

(1) the use of surface-active agents, either cationic, anionic and non-ionic surface active agent can be used, but it must be soluble, stable and can be formed with other components a homogeneous liquid.

(2) In order to improve the stability of the solution of the black hole, preferably PH value of the solution was adjusted using potassium hydroxide or the reagent ammonia.

(3) deionized water as the dispersion medium of the solution of black holes.

3.5 Black hole chemical arts processes and process description

(1) Clean the entire hole processing to water cleaning black hole and processing drying microetch processing water cleaning electroplating copper

(2) Process Description

Clean the entire hole processing: a black hole of the solution within the graphite and carbon black with a negative charge, and after drilling the hole wall surface of the resin negative charge repulsion can not electrostatic adsorption, direct impact on the adsorption effect of the graphite carbon black. By adjusting agent is the regulation of the positive charges, the negative charges of the can and in the surface of the resin brought and even given the positive charge of the hole wall resin in order to facilitate adsorption of graphite and carbon black.

Water cleaning: cleaning the hole and surface excess residual liquid.

Black hole processing: the hole wall surface of the substrate by physical adsorption, adsorption layer of uniform and detailed graphite carbon black conductive layer.

Water cleaning: cleaning the hole and surface excess residual liquid.

short cryogenic processing of high temperature and long time can be used to enhance the adhesion between the graphite carbon black and the hole wall surface of a substrate.

Microetching process: First the solution treated with an alkali metal salt of boron, graphite and carbon black layer to render micro swellable, generated microporous channels. This is because in the process of black holes, graphite, carbon black is not only adsorbed on the pore walls, and also adsorbed in the inner layer copper rings and the surface of the substrate a copper layer, to ensure that the electroless copper plating and copper substrate have a good combination must was removed on the copper-graphite carbon black. To this end only the graphite and carbon black layer generates microporous channels, the etching solution can be removed. Etching the copper layer microporous channels generated by graphite and carbon black layer due to the etching solution, and the copper surface microetch out about 1-2μm, copper graphite carbon black is to get rid of foothold, and on graphite and carbon black in the non-conductive base material of the bore wall to maintain the original state, and to provide a good conductive layer for direct plating.

Check: with the sample aperture mirror or body, as the hole in the surface coating of microscopic examination is complete, even.

Electroplating copper: charged into the slot, and the impact of current, and to ensure that all conductive coating is covered.

Miele electric Co., Ltd. launched the black hole of the printed circuit board technology new method, are shown in Table 1 below:

Table 1 (multi-layer) directly plating process specification

(1) black hole solution tank equipped with a circulating mixing device level production line using ultrasonic the way the best waterjet spray can also be used.

(2) use of an oven or drying tunnel temperature of 80 to 85 ° C, 2 to 3 minutes. Horizontal cold and hot wind drying section should be set. Such as the processing of special materials not high temperature should be 60 to 65 ° C for 8 to 10 minutes to dry; thickness of more than 1.0mm FR-4 or PTFE black hole liquid system and CEM-3 board Drying → temperature to be set at 95 ℃, time 2 minutes.

(3) black hole solution solid line points and PH value of testing on a regular basis. Under the conditions of normal use, the solid line stars will not be reduced, if there stars reduce the phenomenon of the solid line, the use of the MN-701B Miele be adjusted. When the PH value of the black hole is less than 9.5, the activity of the solution was reduced accordingly, and the reagent for ammonia must be adjusted in place.

(4) a black hole liquid storage temperature of 2 to 40 ° C;

(5) on the particular substrate, such as polyimide, polyester, polytetrafluoroethylene and the like, can be used twice black hole of the processing, the process is as follows:

Four quality inspection methods

Direct plating quality of the merits, that is to be analyzed and studied the coating of black holes solution conductivity and electroplating copper deposition rate. Related to the microscopic structure of the conductive coating of the strength of the conductive layer, and with the thickness of the conductive layer and the thickness of the substrate, pre-treatment , prior to electroless copper plating, the resistance value between the PCB board for testing, because the test data may reflect the quality of the state of the conductive layer formed by the direct electroplating process, in order to more grasp the process parameters of the control the copper plating thickening process; while intuitive in a short period of time after copper plating through hole copper coverage to reflect the performance of the pros and cons of direct plating.

Can be formulated for testing or using the following methods:

4.1 direct plating layer quality inspection

(1) the geometry of the test board developed in accordance with the process requirements, select the appropriate number of holes, according to the black hole of the process, according to state and pore size of the pore size distribution of the double-sided without copper plating direct water washing, drying, Determination of the size of the holes on both sides of the resistance value of the test board instruments. Assessment method: 3-5 blocks, randomly selected from the liquefaction process technology to complete black hole PCB without copper plating, determination of the size of the hole resistance of the printed circuit board on both sides with the instrument. When both sides resistance ≤ 100Ω excellent; 100Ω 1000Ω need to check the various control targets, and to make adjustments.

(2) randomly selected from the complete direct plating process PCB three or five by the full board plating (5 minutes), then remove the cleaning normal plating pretreatment , and then to observe the effect of hole plating. If the hole surface is covered with copper, belonging to qualified, if empty, that is required for each control process parameters to be adjusted appropriately.

(3) After the plating of the entire board substrate according microsection program cutting slices do backlight test, such as the hole plating 0-1 translucent points (three hole vias) for qualified, the light transmittance of more than two points for the failure.

(4) using the Hough groove to be tested: the copper-clad board, in the same sheet in accordance with the Hough groove geometry of the intermediate portion of the plate is made by etching method of 0.8 × 50 ( mm), 1.6 × 50 (mm), 3.2 × 50 (mm) of the copper-free area, and then this plate for direct plating process, and air-dried in the Hough tank plating copper areas (normal current is 2A), observed no The time of the plated copper, typically within 2-3 minutes should all plated.

(5) experience to determine resistance test method: because the production of various models of plate geometry size of the aperture, the number of holes is not the same on both sides after direct plating process resistance in the range of fluctuation. To do this, the accumulation of production experience in the production process, a better grasp of the resistance value range of various types of aperture qualified products.

Of course, a lot of direct plating quality detection method, these types of quality detection method is relatively simple, effective, and easy to operate.

4.2 direct plating layer performance testing

direct plating copper, the thickness of the hole copper plating layer of 25μm, was determined after the title aggregate requirements, subject to a thermal shock test as required by the standard, are as follows:

(1) "weldability tester": temperature was controlled at 288 ° C, time 10 seconds, cubic thermal shock test, then made Metallographic sections tested, the hole complete coating, and unprovoked crack, crack.

(2): the product at 260 ℃ HASL through three, and then made Metallographic sections for testing the hole coating integrity defects.

The direct plating precautions

(1) the need for drilling and deburring the same stringent the hole quality requirements is, should ensure that the hole without cuttings, powder clogging, burrs and other defects . The direct plating dried photoimageable i.e. foil, exposure and development. For direct plating to time parked before the film can not be too long, best film direct plating directly.

(2) the graphics before plating degreasing should use compatible with direct plating acidic degreasers. Also note that the optical imaging storage time less than 24 hours prior to plating.

(3) graphics electroplating, plating time should be controlled within half an hour, the cathode current density 2A / d ㎡ to ensure that the hole plating thickness.