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PCB design of electroplating production.

December 31, 2020

2388

1. Electroplating production

Electroplating is the use of electroplating to metalize the holes, so as to achieve the purpose of connecting the layers that need to be connected. In order to complete the metal hole wall with sufficient conductivity and welding at the client later. The material for the hole metalization is mainly copper , But because copper cannot be directly deposited on the resin. Therefore, a kind of media is required-palladium. The thickness of electroplated copper varies according to the ratio between the thickness of the plate and the minimum aperture. If there is a discrepancy between the customer's specifications and the factory's production capacity, please How to deal with it? What effect does plugging and grinding after plating buried holes have on production? Will reducing copper affect production?

Electroplating Desmear&CopperDeposition

After going to the deburr to drill the hole, if the drilling conditions are not appropriate, the edge of the hole has 1. uncut copper wire 2. uncut glass fiber residue, called burr. Because it has to be broken and rough, if not Removing it may result in poor through holes and small holes.

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Desmear is caused by the high temperature Resin caused by drilling to exceed the Tg value, which forms a molten state, and finally produces slag. The slag is generated on the inner copper edge and the hole wall area, which is easy to cause poor conduction. The role of Desmear is mainly to remove Smear to ensure electrical properties. In addition, the hole wall roughness is increased to achieve better hole copper adhesion. At present, the potassium permanganate method is mainly used in the factory to remove the slag.

Electroless copper (PTH) uses Pd deposited in the hole to catalyze the interaction of electroless copper and HCHO to deposit electroless copper. The production process is as follows:

a. After the whole hole Desmear, there is a two-pole ionization phenomenon in the hole, in which Cu presents a high potential positive charge, and the resin and glass fiber present a negative charge. b. Micro-etching is designed to remove the film formed by the entire hole on the surface, and it can also clean the copper surface. Residual oxide c. Pre-activation is to reduce the copper ions formed by microetching into the Pd/Sn groove and reduce the surface tension of the hole wall. d. Activated general Pd colloids have the following structures: Pd2+: Sn2+: Cl-=1: 6:12 is more stable. Then a very thin copper is deposited on the board

Thickened copper Since the thickness of chemical copper is only about 20~30 microinches, it is necessary to do a full-board copper electroplating to proceed to the next process.There are currently three different production lines in the electroplating production line factory, and their working principles are basically the same.

a. The horizontal plating line is mainly used for the plating of boards with laser holes. The minimum allowable thickness is <5mil, and the maximum thickness is 63mil. The size limit is max 20.25x 24.25", min 13.3x14" and the clamping edge distance>0.7" b. Vertical The electroplating wire is mainly used for the electroplating of traditional PCB boards. The minimum allowable thickness is <23.6mil, and the maximum thickness is 150mil. The size limit is max 20.25x 24.25”, min 14x14”, and the clamping edge distance>0.8” c. Continuous electroplating wire is also called electroplating Hole-filling line. It is mainly used for the plating of the plusII board with stackvia. Its process capability has not yet been determined.

2. Electroplating specifications

Electroplating specification introduction

At present, the general specifications for electroplating production in the factory are set in accordance with IPC-6012Class2: PTH hole min0.7mil, buried hole min0.5mil, blind hole min0.4mil. Mainboard PTH hole copper is min0.8mil, AVG1.0mil. If there is a production capacity beyond the above The situation needs to be submitted to the customer for engineering confirmation. The electroplating capacity is closely related to the size of the hole and the thickness of the board. This relationship is represented by aspectratio, and the corresponding relationship is: mechanical drilling: board thickness/minimum through hole diameter, the ratio needs to be <8 :1 Laser hole: (medium thickness + surface copper)/laser aperture, the ratio is less than 0.8. If the aspect ratio exceeds this ratio, a meeting notice must be submitted to the relevant unit before the material is produced to negotiate whether to make it.

3. Plug hole. Copper reduction and grinding

HolePlugging buried holes need to be pressed again after electroplating and making the circuit. If the hole is not plugged, the externally arranged medium will be filled into the hole during pressing, which has a certain quality risk: a Because the glue fills in the buried hole, the laminated medium will be thinner by the outside. b. The medium fills the buried hole during pressing, but it cannot ensure that the air in the hole is completely driven out. If there is air in the hole, When the board is heated, the air expansion may cause the hole copper to crack, and there is a risk of opening. The plug hole ink model currently used in the factory is PHP-900IR-6.

After removing the belt sanding and plugging the hole, the ink in the hole will overflow and bulge out of the hole, and the hole ring will also be stained with a layer of ink, which will affect the conduction and circuit production. Therefore, the board needs to be The ink removal on the surface is usually carried out by physical brushing.

Copper Reduction (Copper Reduction) When customers design special stacks (such as HDI1+N+N+1) and thin circuits (such as 3/3mil circuits) that need to control the thickness of the surface copper, the copper foil needs to be thinned. Copper reduction is based on etching Or grinding to make the copper foil thinner on the board surface. At present, there is a production line dedicated to copper reduction in the factory, and the copper reduction tolerance can reach +/-0.1mil. After the copper is reduced, the ink in the plug hole will be more than copper The surface should be high, and the glue that is higher than the board surface needs to be cleaned by brushing. The processing method is the same as that of plugging and grinding.