1、 Process objective:

 

The substrate will be semi cured with the inner layer of copper foil

 

2、 Inner oxidation treatment

 

1. Oxidation reaction

 

A. Increase the surface area in contact with the resin and strengthen the adhesion between them

 

B. The wettability of the copper surface to the flowing resin is increased, so that the resin can flow into each dead angle and has stronger grip after hardening.

 

C. A dense passivation layer was formed on the bare copper surface to prevent the influence of amines in liquid resin on the copper surface at high temperature.

 

2. Reduction reaction

 

Objective to increase the acid resistance of the gasification layer and shorten the villus height to the appropriate level so that the resin can be easily filled and the occurrence of pink ring can be reduced.

 

3. Comparison of browning and blackening

 

A. The blackening layer is mixed with Cu2O because of high alkalinity in the solution, which is easy to form needle like or feather like crystals.

 

This kind of cuprous long needle is easy to break at high temperature, which greatly affects the adhesion between copper and resin, and causes black spots to flow in the plate with the flow of glue, forming electrical problems. Moreover, it is easy to form local delamination plate after high heat due to water content. The browning layer is granular and nodular crystal with copper surface. Its structure is compact without porosity. The adhesion between browning layer and film is far greater than that of blackening layer. It is not affected by high temperature and high pressure. Therefore, browning layer becomes a necessary process for polyamide multilayer board.

 

B. The blackening layer is thick, and the pink circle often occurs after PTH, which is due to the micro etching or activation in PTH or the reduction of the blackening layer into the original copper color. The browning layer is very thin, so it will not form pink circle. The rough surface of copper foil on the inner substrate is zincified and firmly adheres to the substrate, but the blackened layer on the smooth surface is easy to be attacked by acid solution and shows the primary color of copper,

 

C. Blackening is better than browning because of its long crystal and thick thickness. Generally, defects on copper surface are easy to cover and uniform appearance can be obtained. Browning is often due to the copper in front of the treatment is not perfect and appear mottled uneven appearance, often not recognized by the quality control personnel. However, longer treatment time or higher temperature will be more uniform. In fact, the non-uniform appearance will not affect its excellent peel strength. Generally, the browning performance will be more prominent if the thickness agent and the sealing agent to prevent red ring are added to the general merchandise to make it acid resistant.

 

4. Process Description: after etching, the inner layer board needs alkali to remove the dry film or ink inhibitor. After drying, it needs to be overhauled and tested before entering the oxidation process. The process mainly includes alkali washing, acid leaching, micro etching, pre leaching, oxidation, reduction, oxidation resistance and post cleaning and drying,

 

A. Alkaline cleaning - pickling is also used. There are a variety of professional chemicals on the market, which can remove finger lines, grease, scum or organic matter.

 

B. Acid pickling - adjust the pH of the plate surface, if pickling before, this step can be skipped

 

C. Micro etching - the main purpose of micro etching is to etch the columnar crystalline structure of copper foil to increase the surface area and enhance the grip of film after oxidation. Generally, the appropriate micro etching depth is 50-70 microinches. Micro erosion is very important for the color uniformity of browning layer,

 

D. Pre immersion neutralization - after the board is thoroughly washed, the surface of the board should be adjusted before entering the oxidation treatment of high temperature and strong alkali, so that the fresh copper surface can be pretreated in dark red, and whether there are still bright spots without removing the residual film can be detected.

 

E. Oxidation treatment - the commercial products are mostly divided into two liquids, one is the oxidant, which is mainly composed of sodium chlorite, the other is sodium hydroxide and additives, which can be mixed according to the proportion and heated with water.

 

Usually, sodium hydroxide is easy to form sodium carbonate with carbon dioxide in the air under high temperature and agitation, which shows a lot of consumption. Due to the decrease of alkalinity, the browning color often becomes lighter or uneven, so it is appropriate to analyze and supplement its shortcomings. The uniformity of temperature is also one of the reasons that affect the color. Quartz can not be used in the heater because high temperature and strong alkali will dissolve the silicide. During operation, it is better to let the tank liquid flow and exchange reasonably.

 

F. Reduction - the application of this step has a great influence on the success of subsequent pressing

 

G. Anti oxidation - this step can make the board more reliable, but depending on the product level, it may not always have this step

 

H. Post cleaning and drying - the finished board should be immerged into hot water for cleaning immediately to prevent the residual liquid from drying up on the board surface in the air and not easy to wash off. After being thoroughly cleaned by hot water, the finished board can be completed.

 

5. Key points of quality control in oxidation line production

 

A. Detection method and control scope

 

a. Determination of oxidation amount (O / W) [control range: 0.3 ± 0.07 (mg / cm2)]

 

(1) A 9cm × 10cm 1oz copper strip was oxidized with the process.

 

(2) After oxidation treatment, the test pieces were baked in an oven at 130 ℃ for 10 min. the moisture was removed, and then cooled to room temperature in an airtight container. The weight of - W1 (g) was obtained by weighing.

 

(3) Place the test piece in 20% H2SO4 for about 10 min to remove the oxidation surface layer, repeat the previous step, and weigh to obtain weight-w2 (g)

 

(4) Calculation formula: O / w = (W1-W2 / 9 × 10 × 2) × 1000

 

b. Determination of peel strength (control range: 4 ~ 8 lb / in)

 

(1) Take a test piece of copper foil with the thickness of 1oz and do the post oxidation treatment figure - lay up and then do the pressing treatment.

 

(2) Take a 1cm wide test piece and do the peel strength test to get the peel strength (calculated according to the equipment used)

 

c. Determination of etch amount (control range: 70 ± 30U in)

 

(1) Take a 9cm × 10cm 1oz copper strip, bake it in an oven at 130 ℃ for 10min to remove moisture, cool it in a closed container to room temperature, and weigh it to get - W1 (g)

 

(2) Put the test piece in the micro etching tank about 2'18 "(according to the actual operation time of each factory), after washing, repeat the previous step, and weigh - W2 (g). Then calculate the amount of micro corrosion D. after oxidation, spot check the board with no bright spot as the judgment standard

 

 

 

3、 Laminated plate

 

Before entering the laminating machine, the raw materials for each multilayer board should be prepared for lamination. Besides the oxidized inner layer, the corresponding semi cured sheet and copper foil should also be prepared. The specifications of 1 P / P (prepreg) are as follows: 1080 3313 2116 7628

 

The selection of P / P should consider the following matters: thickness of insulating layer, thickness of inner layer, resin content, and symmetrical area of residual copper in each layer of inner layer

 

The most important thing is to save costs

 

The main three properties of P / P are gel flow rate, gel time and gel content

 

A. Resin flow

 

1. Flow test method: take four pieces of 4 * 4inch film with oblique cutting of longitude and weft, and then stack them together according to the original longitude to longitude or weft to weft. Press them with 200 ± 25psi for 10 minutes in a press which has been preheated to 170 °± 2.8 ° and after fusion and cooling, punch out a disc with a straight diameter of 3.192inch in the central part. Weigh the disc accurately, and then calculate the percentage of glue flow

 

2. Proportional flow rate refers to the use of large pressure intensity when the area is large, and small pressure intensity when the area is small. The method is to tangent the film into a 7in × 5.5in sample, and make the 7in long direction parallel to the meridional direction of the original roll. 18-20 sheets of thin film (1080), 10 sheets of medium film (2116), and it is not accurate if it is thicker than 2116. The hot plate is preheated to 150 °± 20 ℃ and coated with paper. The adhesive is placed on an 8-inch square press at 31 psi or 840 lbs ± 5% for 10 ± 1 min. after cooling, the adhesive is cut diagonally and the thickness of the diagonal is measured with a micrometer caliper. The calculation is as follows:

 

ho=[Wo/n(5.54×10-2)-Wg]×21.2×10-2

 

Ho the original thickness of each film, wo the total weight of the original sample, WG the weight of glass cloth per unit area (g / in2), n-sheets.

 

B. The resin in gel time or tack time film is semi hardened B-stage material, which will soften and flow after high temperature

 

After a period of softening and flowing time, it gradually absorbs energy and polymerizes to increase viscosity, and then hardens to become C-stage material. The time that can flow under pressure, or the working time that can be used for air driving and gap filling, is called gelatinization time or flowable time. When this period is too long, the glue in the plate will flow out too much, not only the thickness becomes thinner and the cost is wasted, but also the copper foil is directly pressed on the glass, resulting in poor structural strength and chemical resistance. However, if the time is too short, air bubbles can not be formed because of too high viscosity before catching up with the gas in the plate reservoir.

 

C. Resin content refers to the weight ratio of glue in the film except glass cloth. It can be measured in two ways

 

C-1 burn out

 

C-2 treated weight

 

F. For volatile components, cut 4-inch × 4-inch sample pieces on the film roll obliquely, weigh them to 1mg on the balance, bake them in a well ventilated oven at 163 °± 2.8 ℃ for 15 ± 1min, then take them out and put them into a closed drying dish to cool them to room temperature, and then quickly weigh them again. The ratio of weight loss to original weight is expressed by percentage method, which is the content of volatile components.

 

2. Lamination operation A. principle of combination the combination method has a variety of options according to the customer's specifications, considering symmetry, copper thickness, resin content, flow rate, etc. to meet the quality requirements at the lowest cost

 

(a) The basic principle is that the insulating dielectric layer between two copper foils or conductor layers should be composed of at least two pieces of film, and the thickness after pressing should not be less than 3.5 mil (the requirement of more sophisticated plate is thinner than this), so as to prevent the copper foil from directly pressing on the glass cloth to form bad insulation with too large dielectric constant and poor adhesion.

 

(b) In order to make the glue flow to fill the gap in the plate, and not to cause too much glue to slip or excessive expansion in the Z direction, the original thickness of the film in contact with the copper surface should be at least twice the thickness of the copper. The outermost layer and the sub outer layer should have at least 5 mils to ensure good insulation.

 

(c) The warp and weft directions of the thin substrate and film should not be mixed up. The warp and weft must be aligned to avoid the irreparable result of the later warping. The number of films must be symmetrical up and down to balance the stress. It is very important to use less hardened C-stage materials to make up the thickness, especially for thick multi-layer plates, so as to prevent the separation of the interface after heating. When not in use, pay attention to its moisture baking and surface coarsening to increase adhesion.

 

(d) After the copper foil is stacked, the dust cloth should be used to gently and evenly rub on the smooth surface. On the one hand, the space air should be removed to reduce wrinkles, and on the other hand, the impurities on the copper surface should be eliminated to reduce the later depression on the plate surface. But be sure not to touch the rough surface to avoid poor adhesion.

 

(e) Choose a good combination mode, and fix the inner layer and film of more than 6 layers with rivets to prevent the sliding plate from pressing. Here, we need to consider the selection of rivets (length, depth, material), and the operation of riveting machine (fixation tightness), etc

 

C. The temperature of stacking environment and personnel stacking site should be controlled at 20 °± 2 ℃, and the relative humidity should be 50% ± 5%. Personnel should wear one-piece anti-static clothing, hoods, gloves and masks (to prevent skin contact and moisture). Cloth shoes should be blown by air for 15 seconds before entering the room. Personal belongings should not be brought in. At the entrance, a rubber mat should be set on the ground to stick the dirt on the soles. After the film is taken out from the cold storage and cut, it must be stable in the room for at least 24 hours before it can be used for stacking. To complete the combination of stacking, the pressing on the machine should be completed within 1 hour. If there is a vacuum device, it should be pumped for a period of time before pressing to drive away the moisture. Too much moisture in the film will cause TG reduction and hard to harden.

 

D. Laminated plate method

 

(a) Tip less pressing plate method - in this method, the multi-layer plates between each partition in each opening should be aligned up, down, left and right, and the partitions should also be aligned up and down. Naturally, the openings of the whole press should also be aligned in the center.

 

There are two ways of alignment

 

One is the projection lamp type, in which a projector is installed directly above the stacking table. First, the aluminum carrier plate is positioned and added with kraft paper, and the light and shadow are projected on the aluminum plate according to the size of the book. Then, the contents of each book and the partition plate are stacked one by one. Finally, the kraft paper and the aluminum cover plate are pressed to complete the combination of an opening.

 

- the other is to find out the middle point of each side of the material of the sheet when there is no projection lamp, and the middle point of the aluminum sheet steel plate can also be found out, and it can also be aligned up and down.

 

If there are two rivet holes in each of the four layers of film, the relationship between the rivet holes in each layer of film and the inner holes of the four layers of film should be taken carefully